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Taulman3d Alloy 910 - after several rolls....

posted 25 Apr 2016, 13:51 by Colin Bell



It's been a while since my last post, since my youngest daughter was born, so apologies for the radio silence. What time I do get though, I've spent building a new larger format Kossel Delta machine, which is now finally commissioned and printing, and also revamping my triple head Mendel. I'll do separate posts on both of these as I've learned some interesting things along the builds which I'd like to share.

Of course, not having time to blog in any detail doesn't mean that all activity stopped - babies do sleep very occasionally, and when my little treasure does, I've been able to catch up on some 'fire & forget' printing to catch up on my backlog of personal parts that required creating.

Many of the parts that I needed to create needed high strength, stability in high temperature environments and ease of machining in terms of drilling and tapping. In the past, this has always meant ABS for me, however my recent love affair with Nylons kept bringing me back to the Taulman3D range, and in particular their Alloy 910 material. I've previously blogged about Alloy 910 based on a small sampler pack I had of it, and since going out and buying several spools of the stuff, I wanted to expand on it here a little as I've had a phenomenal success with it in a variety of applications.

One of the key reasons to use Alloy 910 over ABS is the fact that it doesn't warp - not even a little bit. And that delamination issue you always get with bigger ABS prints? Forget it - you can't get this to delaminate with a hacksaw easily, so a cool draft isn't going to bother it. This makes it an ideal material to use in place of ABS on machines without a heated enclosure, which is most of my 'bot farm. The Deltas and Cartesians all work well with this material with zero modification of my usual setup - of course your milage may vary, depending on your machine, but providing you follow some basic rules below, I absolutely guarantee that you'll have no issues using this stuff.

First rule up, is your bed cover of cover of choice - previously I used Kapton tape or Painters tape either on an aluminium build surface, or a sheet of glass. With PVA glue (Glue-stick) this works OK with nylons, but I did get considerable warping. I then tried a sheet of Tufnol clipped to a cold platform, and the adhesion of Nylons to this is astonishing - it's so solid that getting the part off can be a major headache. 



As regular readers will know, I've added PEI sheets to all of my machines now, and Nylons will stick very well to this provided it's heated to around 60c. For smaller, low surface area and low density parts this is just fine, however I've now found the perfect combination for those huge 100% unfill parts in Alloy 910 (drum roll...) a heated PEI bed (60c), with a light (criss-cross pattern) layer of glue-stick on it. This keeps the part solidly on the bed for the duration of the print, and a light spritz with tap water around the base of the model following print completion, means that it can be removed easily from the bed with virtually no effort. Since using this method, I've had zero failed prints and no warping or delamination even on very large parts. The box part in the picture shown here is 170x170x170mm, and the bottom layers are 25% infill with 5 bottom layers. Try that in ABS on an un-enclosed machine...

Of course, you need to be sensible with your printed part in Alloy 910, as with any material - I've found it likes a uniform and gradual cooling from the 60c of the bed. My best practice is to leave completed parts on the bed following printing, and let the bed and the part cool naturally to ambient room temperature before attempting removal. On occasion when I've need to pull the part off to start the next print, I've seen some very minor corner warping - this issue disappears completely though, as long as you let the part cool fully before removal from the bed.

In terms of layer height and high detail, the material is as capable as most, and I've not had any complaints. The surface finish is a lovely glossy surface, and it will show up detail well, particularly when dyed with an acid based dye (such as Rit Dyes), however that's not really what I use this stuff for - most of the parts I create with it are industrial strength functional parts, not pretty display items - but I'm sure it would be capable. In terms of the surface finish, a very stable hot end temperature is required - one of my machines developed a dodgy thermistor which caused the temperatures to fluctuate by 20-30c up or down of my target print temperature of 245c, and this was very noticeable on the part. I could literally see where the temperature spiked up and down on the part as it printed due to the change in surface sheen and smoothness. This didn't detract from the functionality of the part though (and it's living happily in my washing machine as we speak!)

One thing to watch though is very low layer heights - I mistakenly started a print at 0.05mm instead of the 0.25 it should have been, and the layers looked very messy.

In terms of infill, I've had excellent results from 100% infill, all the way down to 5% - all the parts are very solid, and the less infill used obviously allows for more flexibility in the finished part. I've found that for highly flexible part requirements, using 5 shells and anything between 5 and 15% infill gives the best results for durable flexible parts. I can honestly say I've not had a single Alloy 910 part break on me either, even a replacement door hinge supporting a door weighing almost 20kg shows no sign of wear after nearly seven months use.

Another thing which I mentioned previously is that as with most nylon based materials, Alloy 910 tends to 'spider web' a little during printing, and depending on the models and how far the hot end needs to travel, these can collect on the nozzle, blacken and be deposited back onto the print. I've found that use of an Ooze shield setting, combined with a .1mm Z lift on layer changes, retraction and travel moves virtually eliminates this issue. My retraction values for my bowden machines are pretty small at 3mm (3000mm/min), so the above additional slicer settings helped dramatically. This is less of an issue in direct extruder drive machines of course, but I'm tending towards bowdens most of the time to keep my hot ends lightweight.

Drilling and tapping of Alloy 910 parts is very good - being a nylon you need to run drills and taps slowly and clear the tools often to avoid them clogging, but other than that there are really no issues. Glueing Alloy 910 is possible, using Tetrahydrofuran...which is not your average hobby shop accessory. I've actually had a lot of luck with Gorrilla brand Superglue though, it stays liquid for around 4 hours, and then over the next 2-3 hours sets like concrete and will join parts together. This is good where no flexing is required, as like all superglues, it can be strong but brittle under axial forces. My preference is to design holes and alignment guides into parts, and then use nuts and bolts wherever possible.

Clean-up is also a non issue, just a sharp blade run lightly over the surface is all that's required on most prints. This is a good thing too, as I mentioned in my previous post, this material is extraordinarily blade resistant. This of course is an issue if you need to use supports on a single material machine - removing supports was nigh on impossible without violence when I first started using this material, and I was about to build a purpose designed dual extruder printer so that I could use HIPS or PVA as a support material to get around this. However...I've had another breakthrough in this area (bit of a facepalm moment actually!) where I found that the issues I was having with my supports where down to the slicer I was using.

I'd been an advocate of the excellent Slic3r application for around three years and didn't even consider that the issues I was having with Nyons and support could be caused by the way it creates the support structures. I recently purchased Simplify3D (long story, later...) and threw a model requiring support at that and printed in Alloy 910 just to see what happened. What a difference! 



The way it created the support structures is just so far ahead of Slic3r's current algorithms, and the fact that you can add custom supports makes a huge difference in any material, but with nylons, it actually makes using supports on a single extruder machine possible. Removal of the support material generated in Simplify3d is literally effortless, and leave virtually no surface defects. It really is the best $150 I've spent this year, for support structures alone.










For those interested, here are my support settings for Alloy 910.

 

In closing, Alloy 910 is now a firm favourite material for me to use, and its capabilities continue to surprise me. If you have a need for stronger than usual, flexibility and high tolerances in heat, then I can't recommend it more highly.


Huxley RepRap Rebuild

posted 21 Nov 2015, 04:56 by Colin Bell   [ updated 2 Dec 2015, 22:56 ]


My first experience with 3D Printing came with the Huxley pictured to the left, way back in 2011, in which the build experience and learning was documented on several blog posts here. This little printer will always be dear to me, as apart from being my introduction to 3D printing in general, it also got me through several months of illness and taught me a great deal about engineering machines with moving parts, designing and manufacturing complex and functional parts, how to interpret some very experimental guides and use cases. It also opened my eyes to the fact that machines in general are creations that can be modified to do exactly what you need them to do, as opposed to what a manufacturer wants you to use it for. Long live open source hardware!

As with most first attempts though, although the building and seemingly endless calibration gave some reasonable printed results, it never produced anything close to the quality I had in my mind's eye. Sure, parts were functional, and some of them are still in use today, but for the most part they were not even a little bit on the pretty side. 

There were a number of factors which caused my aesthetically not pleasing parts - my own mechanical mistakes and dodgy engineering skills of course, of which there were many, old school slicing software (does anybody still use SkeinForge?) inaccurate flow rates and speeds, bed not being level, poor quality filaments...the list goes on. Combine those things with the fact that the design was based on stuff laying around in a machinists shop and the legacy was based on mature but not perfectly suited CNC tool-path software and methodology, and your 1st Gen' Frankenstein Cartesian plastic spitter was at best a great concept, but not the speedy, highly detailed model producer you imagined it would be. 

But, it inspired me to follow developments and also make my own improvements. It also introduced me to a large community of like minded tinkerers, creators and engineers on forums, and of course has quickly developed into the medium-large(ish) industry that it is today. My current production machines are faster, more accurate and repeatedly produce the kind quality that I only dreamed of back then - with about a 10th of the hassle to boot. But without the old Huxley, I'd never have gotten the bug, and it's for this reason that I decided to pull it off the shelf, blow off the dust and recondition it with a few modern additions to make it a useful machine again.





Visually, you can tell this device was a constant work in progress. The wiring is a disaster from several quick repairs, the electronics just hanging off the side, Molex interconnects replaced with quick and dirty solder and tape, and there's more cable ties than you can shake a stick at. Clearly all of this needed to be addressed. Obviously, wiring tidy up is one of the last jobs on any build, but I committed to at least make it look safe, if not tidy. The open frame design makes it impossible to completely hide the wiring, but at least it could be rationalised.


The most annoying thing visually by far was the frame mount I'd hung the Sanguinololu electronics in, and the cable tied power switch. I decided that I wanted the electronics to be mounted within a separate enclosure, along with the power switch and inbuilt cooling for the stepper drivers.







I started by designing a basic chassis to house the Sanguinololu, with two separate side boxes - one for the power switch and the other to house the power input and hide the wiring. The design was made as usual with 123D Design, and printed in ABS so that I could Acetone weld the parts together later (this works very well by the way and produces a much stronger bond between parts than most glues). I also created a top for the boxes, which has a hole for a fan, and also a simple slide mount for the display to be added later. The fan in use on was a cheap 5v axial, and the incoming voltage to the Sanguinololu was 18v, so I put a simple 5v regulator (an LM7805) mounted on a bit of strip board to supply it. 

I also created a custom bracket which fits into the boxes, and then can be bolted onto the existing support rails of the Huxley. This arrangement along with the addition of modular Molex plugs on all the cables means that the electronics can be removed when the machine is being moved around, or left in place permanently.

As you can see from the various pictures, I went through several iterations of the design, however the basic design stayed pretty much the same.


Unfortunately, I don't have a picture of the finished case fitted to the printer, and tidied up properly, but these shots should give you the basic idea. 

It did all seem to work OK anyway, so I moved onto the next thing. If anybody needs a modular box for their electronics, it can be found here.































Next up was the mechanical side and I could see a couple of minor, but nonetheless impacting issues with the machine as-was. In terms of frame, rods and bearings, it all looked pretty much solid, however when I built it, I only had the printed parts which were supplied in the eMaker kit, and I had no CAD design knowledge to easily replace them if they broke. Given that the parts used on this were from the 2010 Indiegogo campaign, they were quite rough in terms of quality, and also some parts were not particularly strong due to design constraints of the time. Over time, use and abuse, some of the parts had required repair with glue or heat welding, and also due to the fact that I only had a limited amount of filament on hand and no easy way to get more, I didn't print spares. These days, my store carries around 100kg of materials of all descriptions at one time or another, so I carefully inspected all printed parts, and created new versions as required. In particular, the X-ends had very weak slides where the bushings sat to hold onto the smooth Z rods, and also never had a very smooth belt path, so I reprinted those using an updated version. 








The Z couplings also required replacing, along with the PTFE friction fit tubes used to hold the Z thread rods to the motor shafts - those things always managed to work themselves loose, usually leaving the Z axis only lifting on one side during a print - very annoying. A touch of two part epoxy and the couplings printed at 99% normal size fixed that issue permanently.



The extruder that was fitted, had proven to be very reliable, however it was noisy, using PLA printed gears and additionally the bearings inside were heavily worn. The design of the original wasn't the actual 'original' though, it was a design from the times when the choice of filament colours available were white or eh...white. This extruder was special in that it had holes within the filament path allowing you to stuff coloured pens into the filament as it passed through - instant coloured prints! Well sort of - it worked after a fashion. I remember I ironically printed this colour changer using a sample of blue & silver speckled filament which actually looked great. For the rebuild though, decided to go back to the original design, but slightly enhanced with ABS Herringbone gears and shiny new bearings, which produced a virtually silent extruder that made a light whizzing noise rather than the bone rattling racket it previously made.


One of the most annoying parts of any 3D printer is the dreaded hot-end block, which often requires a complete strip down of the hot-end, and liberal use of Napalm and Atomic weapons to clear. Well, maybe not quite that bad, but trust me, the original hot-end on the Huxley definitely fell into the clogged more than not category. In retrospect, this was down to the Bowden tube setup and software controlled retraction being an unknown black magic art at the time. Whilst I suspect that this could be largely fine-tuned these days with better knowledge of what's actually causing the problem (after all, I have other Bowden set-ups with no oozing or clogging issues these days), I decided that I wanted to move from the original hot-end and replace it with a modern version. 







I decided on a stock 0.4mm Ubis hot-end from PrintrBot, largely because I had it lying around, but also because I've never had a single problem with them.
Of course, this required a complete redesign of the original carriage, again which I created in 123d Design. I used a couple of existing designs available, and added my own modifications to mash up a new carriage which sports a filament fan, and improved belt guides and grips. One of the challenges was designing the mount so that the taller Ubis would fit through the gap at the top of the frame, so as to not lose any Z height. Overall, I think the design of this part, building on other people's excellent designs was one of my favourite parts of the entire rebuild. The addition of three new high quality linear bearings completed this part of the project.




The X carriage/Ubis Mount models, and further details are available here for anybody that needs them.






The next thing that required some TLC, was the original Nichrome wire based heated bed. I've already blogged about this particular upgrade in a fair bit of detail here, so won't cover it again. I will just say though, that replacing the Nichrome with a modern, safe and efficient silicon pad, was the smartest move I made on this project - I'm pretty sure the Nichrome bed had me on its hit list for one day...



(Yep, thats how the wiring looked on the Nichrome bed after a couple of years use...I'm pretty sure it would have killed me somehow at some point!)





Of course, while I was working on the heated bed, I cleaned off all the old Kapton tape and prepped the surface with a nice new PEI sheet. Well, it would have been rude not to, right? 
Model to bed adhesion during printing was always an issue on this machine, partly due to bed leveling, Z height and uneven heating - the PEI all on it's own takes care of around 60% of the issues, with another 30% down to even and reliable heating - the other 10% is bed leveling and consistent Z height before printing. As mentioned before, the Z couplers help a lot with the consistent Z height issues, and by putting smaller, stiffer springs under the bed I was able to virtually eliminate that last 10% as well.

Readers of this blog will be well versed with my love affair with PEI, and I have it installed on all of my production machines now. If you want to read some of my reasons and impressions, have a look at this post.



Mechanically, the printer was ready for action again at this stage, however I felt that to truly modernise it, it needed a display and rotary encoder - well it is 2015 for goodness sake! No self respecting machine is complete without a display, and the rotary encoder means it can be used without a PC, which is surprisingly handy on a small portable machine like this. I've made this upgrade to all of my printers now, and can't imagine not having it there anymore. Looking around in my spares bin, I found one of the original Panelolu displays, which I'd actually bought for this device over three years ago from Think3dPrint3d but never gotten around to installing.












The kit comes in component form, and consists of a PCB for the buttons, LED and rotary selection switch, MicroSD card reader and of course the display module itself.

Wiring was achieved with a ribbon cable, and the schematic to get this right is here, however I must admit I struggled to read the schematic correctly and ended up following simplified instructions from the Soliforum unfortunately although the post is still available, the pictures are all missing, so I've contacted the original author for permission to repost the offline copy I have of it here.











The only thing to look out for if you make one of these, is the length of the ribbon cable which goes from the display to the controlling electronics - any longer than 15cm on this design and the display doesn't work. I've had similar issues with these panels in the past, so my guess is there is a signal loss that cables of longer than 15cm generate and the displays cannot compensate for it.

Additionally, I printed a case for the display hardware, and a simple stand which would slide into the box I made for the electronics, mounting the display on top of it. The case itself is based on the Think3dPrint3d design, however I designed in a spacer in order to give the wiring a bit more space (yeah, I added some additional electronics to play with).








Of course the printer's firmware will need updating in order to use the display and encoder - as the Huxley had a three year old firmware on it, I upgraded to the latest Marlin code and modified it for the Huxley's specification including the added display and encoder. Because I'm writing this article some months after the event, I won't go into the details here as it's all a bit hazy now (I'm getting old...) but if anybody needs help with this aspect, just reach out to me and I'll be happy to try and help out.

Apart from a bit of belt tensioning, and getting an initial level on the Z axis and bed, the hardware side was complete now and I headed into the calibration stage - previously this had been a never ending task on this machine, but I'm pleased to say that all the upgrades actually made it very straightforward. The only real challenge was getting the e-steps/mm right for all the axis' as initially every print was too large by around 4mm - this wasn't too bad to sort out, and I had a nice pile of calibration squares once complete!

The new heated bed worked like a champ' as expected, and heated up in no time. The Ubis on it's new three bearing carriage also performed flawlessly and was producing excellent prints in no time - there was a big of stringing going on due to the Bowden setup, but this was easily fine tuned in the retraction settings. Additionally, the new stiffer springs in the bed made levelling it much easier, and the new Z couplers meant that once it was set level with the bed, it stayed there.








One of the objects I printed with the Huxley back in the day, was the requistite Yoda bust, so I re-printed it with stock settings to see how they compared - the original is on the right and the new version on the left - not bad I thought!









So the next step was to get the machine to it's new owner, my son. We currently live in different countries, so I carefully packed up the printer, with a bunch of handy spares and some filament, and lovingly loaded it into the taxi - of course when getting out of the taxi at the airport, the bag got dropped, smashing a couple of plastic parts on the X axis...but fortunately, part of the 'My First 3d Printer' kit I'd put together for my son included a full set of spares. This meant he got a live masterclass in replacing parts on his first view of the printer, which was kinda fun although I swore quite a bit as you can imagine! The lesson here is that there is a reason why the pro's package things so carefully and don't just chuck them into a duffle bag!











Mini-Kossel Delta Printer

posted 22 Sep 2015, 12:47 by Colin Bell   [ updated 22 Sep 2015, 12:48 ]

 I've been building and using variations of Cartesian machines for almost four years now, and have been through several generations of these fascinating and practical machines, from Huxley's, Mendel's and Printrbots. One variant I had yet to try is a delta printer, and after seeing a few in action I had to get one in to see how they ticked. For me, once the build, the calibration and fine tuning are done, my machines tend to become trusty tools rather than passion items, so I'm always on the lookout for the next one which will teach me a bit more engineering in one way or another. 
Delta robots are strange beasts to the uninitiated - the idea is that the tool head (a hot-end in the case of a 3D printer) is held flat in relation to the print bed at all times, suspended from three pairs of parallel rods, which move up and down on carriages connected to the three vertical sections of the frame. By moving the carriages independently to each other, the robot is able to move the tool head extremely quickly to any point in space within its defined boundaries, and be able to do this very accurately and with an extremely high degree of repetition. 

When compared to the X/Y/Z co-ordinate system employed by Cartesian robots, I can see why the Cartesian design was dominant for so long - the maths involved in Delta robots might seem like a good practical high school trigonometry lesson at first glance, but when you're calibrating to sub-millimetre accuracy, its enough to put a lot of hobbyists off early on. Additionally, the computational power required to keep these things pumping out translated g-code means that the standard Arduino based systems struggle to keep up, although optimised firmware code can enable this to work out these days. To get the best from a Delta robot though, a beefy CPU is recommended, especially if you intend to use a display - something like the 32 bit, ARM core SAM3X8E used on Duet electronics for example. More on that later.

Saying all that, if you find yourself gazing for long minutes at your pride and joy Cartesian printer doing its thing, you're going to love watching a Delta - its fascinating to watch as the carriages move up and down completely independently of their cousins on the other axis' with an accuracy which completely puts a lot of legacy machines to shame. Combine that with the sheer speed these are capable of printing at (think 320mm/s at full chat compared with 50-100mm/s on an average Cartesian) make them a joy to behold.

So, obviously I must have one...so I went to speak with my friends at Think3dPrint3d (T3P3) knowing that they would have a good solution for me to consider. I already knew from their blog posts that they'd been working on a derivative of Johann Rocholl's Mini Kossel Delta 3D printer, and already knowing their high quality R&D and enthusiasm for 3D printing in general, choosing them to supply the parts was a no-brainer.

I could have gone the route of purchasing all the various parts independently of course - the design is open source and plenty of people have build logs available to refer to, 
but buying a kit takes a lot of the headache out of sourcing and matching up components - yes, you can get very high quality components and put them all together from different sources, and you might even save some money in the process, but honestly, not a lot, and these guys seem to use very good quality parts, rigorous in-house testing and customer feedback to good effect. The kit they supply consists of less than 200 parts (not as much as it sounds when you consider every nut, bolt and washer is counted), and they have very good illustrated build guides available, along with excellent customer technical support by email.

The supplied kit includes fittings, fixtures, Nema 17 motors, belts, guides, bearings, fans, carbon fibre rods, rollers, cable ties, e3d v6 hot-end, Mitsumi 1515 aluminium frame extrusions, bowden tube....everything required. 
The standard kit comes with a RAMPS 1.4 shield and Arduino 2560 Mega board, however after reading some reviews about Arduino's struggling with Delta's, I decided to upgrade to a 32 bit, ARM core SAM3X8E Duet board, and a touch screen display. Well why not?


Also included are all of the various plastic parts that are required - again, these can be printed on your own existing machine, but it's upwards of 25 hours printing on a reasonably fast printer, which might be a consideration. The parts supplied by T3P3 are supplied in your choice of colour, printed in ABS. All parts are pretty solid and well up to the task at hand. They are supplied 'unfinished', meaning you need to clean them up a bit, however you are also supplied with some handy tools for assembly, including a craft knife, hex keys and a 3mm hand drill, so even if you have no tools of your own, you will have the basics with the kit. The finish on the parts is not the best I've ever seen to be honest - they are supplied to be solid and functional, in which they excel. I suspect that the parts are printed at around a 0.4mm layer height. 

On a couple of the larger frame parts, I found some cracking and de-lamination which is not uncommon on larger ABS models - a quick blast with a hot air gun followed by the part being clamped until cool sorted this out in all cases, and I've had no issues with either strength or further de-lamination.

Assembly is very straightforward following the supplied documentation which I'm pleased to say is updated very quickly when minor items need clarification. 

In fact, I'd like to highlight the excellent customer support I always get from Roland and Tony at T3P3 - I guess I'm one of 'those' customers with way too many questions, but I never seem to phase them - they always welcome my comments, respond to my questions, and are very flexible in terms of sorting out quality or component issues quickly - I'll cover a couple of these in later paragraphs, but I want to be clear that Think3dPrint3d are first rate in customer support - it's rare, and here are some role models!



Physical assembly of the Mini-Kossel took me around four evenings, including clean-up of the ABS parts, which I took some time over to get a good finished look. I followed the supplied documentation throughout the hardware assembly, right up to the wiring section, which is where my build differed as I'd decided on Duet electronics instead of the stock RAMPS 1.4 set-up.


T3P3 are also on the design team who created the Duet incidentally, a fact which I hadn't realised until I found this out on the RepRapWiki. The board has all of the stuff that a RAMPS shield is normally used for, such as stepper controllers, MOSFET power drivers for the heaters, fan/power outputs, Ethernet and an SD card reader etc. It's also expandable with an additional board to run a total of 9 axes controls (3 axis + 5 extruders for example). Plenty of room for future upgrades then :)

Additionally, and most importantly for me, it will also support a colour touch-screen interface, which I decided early on was a must for my application, as I wanted to be able to use the printer completely PC independent if necessary, and...well hell, this is 2015 - give me a touch-screen for goodness sake! The touch-screen I used with the Duet is the PanelDue, and was also supplied by T3P3.

The firmware for the PanelDue is created and maintained by David Crocker (DC42 on the forums) and the Duet's firmware is based on Adrian Bowyer's RepRapfirmware that is already familiar to many users. 
David has provided very detailed instructions on his blog which help the adventurous to upgrade a Mini Kossel to use the Duet electronics.  Also of course, he supplies instruction on how to update and install the PanelDue touchscreen interface which he produces.








I used the supplied wiring loom for my build, and simply extended all of the wiring to the correct length. I'd decided early on, that because the Duet board wouldn't physically fit into the base underneath the bed, that I'd mount the electronics onto the back of the Z axis tower, so all my wiring was extended to facilitate that.









Once fully assembled, and the Duet firmware upgraded to the DC42 fork, it was time to do some motor testing, check heaters and thermistors etc - all checked out good, so I sat back to admire the build so far, before moving on to actually trying to print anything. So, in with the traditional virginal white filament and set heaters to max!

No extrusion. Lots of clicking and filament grinding in the extruder, but not a sausage coming out of the e3d v6 hot end.

Must be too cool, maybe I made a mistake with the thermistor calibration? Checking with a thermocouple and showed it was within .2c of the 235c this filament usually likes on other printers. Hmm, crank it up a bit then - 240...no..250..no....255 <starting to sweat a bit>...oh! I see a bit coming out! There is goes at 255c! Lets get a print going! I must have made a mistake with those thermistors!

Skirt printed, looking good! First layer half done and....no extrusion. Darn!

OK, must be the e3d v6 blocking - lets check it - no...I see daylight all the way through. Check retraction - all within the recommended 3mm maximum. Well, its got to be the extruder right? Nothing else left! 

At this point I noticed that the bolt driving the large gear on the extruder was occasionally just spinning without turning the gear, and looking through the extruder end to end I could see the path wasn't clear. After some advice from T3P3, I ran a 3mm drill through the extruder body and used some epoxy to secure the bolt into the large gear. I then reassembled the extruder and paid particular attention to the build instructions, ensuring that it could push and pull filament through at high and low speeds without issue. 

Once installed, I tried just extruding for a while without actually printing anything and observed that the extruder was frequently binding and producing a clicking sound, normally associated with not enough current going to the extruder. Fortunately, the Duet firmware allows you to change this in code, rather than messing about with a fiddly adjustment pot on the board, so I increased this to the maximum it would allow, and it was a little better, but still skipped occasionally - enough for me to know that I'd never get a clean print from it. I have to admit I was quite stumped at this point, and even T3P3 were struggling to give any advice. At this time I was also travelling for work, so progress was spotty for a couple of weeks, which doesn't help when you're trying to troubleshoot effectively. To cut a long story short though, I ended up changing the e3d v6 for an old one used on my Mendel - this worked fine, and it was only when I had the e3d v6 nozzle inspected under a microscope I found scoring inside, where on my old one it was smooth. I'm not sure if this is a manufacturing defect but it was the root of the issue - I put my old nozzle on the new v6 and, hey presto everything started working as expected. T3P3 sent me a replacement e3d v6 which when installed, worked flawlessly, and has done ever since. The upshot of this though, is I lost around three weeks messing around with the hot end, bowden tube, extruder and thermistor settings when I could have been printing...but then again, I bought this to learn from as much as use so I don't consider it a fail at all, especially with the speedy replacement hot end.


Now that the printer is finally capable of producing prints, it's time to add the touch-screen display and do some final calibration. A note on the final calibration - if you build one of these T3P3 kits, do take the extra time and do some additional calibration - I found that the Delta produced prints which were an equal in quality for my Printrbot and Mendel in medium quality modes without any final calibration. In fact I was very impressed - for a casual user or somebody who doesn't want high detail this machine will produce functional good quality parts (not ugly either!) right off the bat. 




Due to the e3d v6 being a very capable hot end, the printer is also able to use a wide variety of materials to print with - PLA, ABS, Nylon and composite metal or wood materials up to 300c should be supported. The heated bed is able to heat quickly up to around 130c and hold it there without issues. One of the last assembly items I installed, was a sheet of PEI adhered with 3M transfer tape - see my other posts on PEI for details on the advantages and methods.





In order to fine tune calibration on a Delta machine, you need to kind of rethink what you know about Cartesian calibration. Sure, some thing are going to be the same - E-Steps per mm, ensuring that the bed is level and extrusion rates calibration are all the same, and are covered in the T3P3 documentation, and also in David Crockers blog, along with a lot of others out there. However that is about the limit of what you can compare with Cartesean machines. I'll jump through the main steps I went through briefly here, and leave out a lot of the stuff that made me scratch my head - I won't do a great deal of detail though, so if the resources I list are not enough for you, feel free to mail me for more details on any particular point. In particular, endstop calibration as per David's instructions may be a little confusing, especially his explanation on setting up the Delta Radius - I will do a separate article about this one.

As you can see from the picture on the left, my bed appeared to not be level, as the plastic isn't being distributed equally over the bed. Looking at it with the Z-axis at the back, X-axis to the left and Y-axis to the right, you can clearly see that it's producing a nice bead of plastic from Y > Z > X, but from X > Y is smashed flat on the bed. This creates a couple of issues, firstly, tall prints will be noticeably not straight the taller they get, and secondly, removing parts from the bed will be difficult and potentially you can cause your parts to de laminate as you pry it off the bed - this is illustrated in the picture of the yellow parts, were you can see how the bottom layers broke off the parts and remained on the bed.

Checking with a digital level showed me that the bed was actually perfectly flat in relation to the frame, and my PEI sheet was also very well stuck down and not bowing up - I checked this with the bed both cold and hot. What I found in the end, was that my X and Y towers are leaning very slightly in the outward X direction as a result of a barely perceptible bend in X frame extrusion. The only way I could actually gauge this, was by holding a flat ruler along its length, and checking for any gaps between them. This showed that the bend is causing the X tower to lean, and is throwing out the frame geometry by around 0.23mm. I know this doesn't sound like a lot, but as can be seen it's made a difference. The way I got my fine measurement of how big the bend was, was by following the endstop calibration' routine in part 3 of David Crocker's blog. No matter how many times I tried to get the endstops perfectly calibrated, my calibration print (the round one above) showed the same results, even though the maths showed the endstops adjustments were spot on. Once I'd figured out the issue though, I had two choices - either dismantle the printer and try bending the extrusion to make it perfectly straight, or try to sort out the issue in software. I opted for the latter, and in the end this turned out to be a simple solution - just do the normal endstop calibration, and then raise the X and Y settings by 0.23mm. Following that, adjust the Delta Radius and print height to account for the changes, and you're good to go. Easy!


For illustration of the difference this minor change made, please see the picture to the left (the parts are sitting on a different printer, but were actually made on the Delta - I just took the picture here for lighting reasons).

The smaller part on the right is before the above calibration, and show some curling due to bad adhesion, and you can see on the extreme right of the part that the outer wall is leaning out slightly - on the print bed this wall was pointing at the X axis. The part on the left, was after calibration and shows perfect adhesion of the support material and model, and zero curling or leaning on the walls. The parts are straight off the printer in the shots below, and haven't been cleaned at all, showing the e-steps are spot on.








Now that I was sure the Delta could produce good prints, I moved onto the touch-screen display. As I mentioned 
previously, I am using the obvious choice for Duet, which is David Crocker's PanelDue. This was supplied by T3P3 along with the rest of the kit. Electronic's installation is very straightforward, and covered on the above link, so I won't go into it here.
I decided to change my implementation a little because I wanted to mount the display at the top of the printer between the X/Y frame extrusions. Although several enclosures are available, I ended up designing my own to allow this.

On the supplied electronics, the control board is designed to sit off to the side of the LCD screen, mounted on a simple 40 pin connector. This would make an enclosure too wide for where I wanted to place it, so I hacked together a straight-through 40pin connector from the LCD display to the controller so that I could mount the controller on the rear of the display. If you happen to have a retro 40pin ribbon connection from an old CD-ROM or IDE HDD, this would likely work just as well as all you need is a straight through connection for each pin.







The next point that needed addressing was the Duet's enclosure. The one advertised on David Crocker's blog is a good design,
 however it's for a version of the board which has pin headers instead of the screw terminals installed on mine. Rather than pinch the cables, I simply expanded on the design and made a few changes to suit my application, such as making the port holes a little larger, adding additional holes for the bed thermistor cables, and making a cut-out for the incoming wiring.













No enclosure is complete without a cover, so I designed one for this one too, in a transparent plastic so that the board's status LED's shine through. Rather pleasing I thought.











The last part I needed to update was the included top mounted spool holder. The supplied one works a treat, and has a nice smooth action due to the included bearing, however it didn't fit all the spools I wanted to use, for example the Taulman nylon 1lb spools, which have a very small hole in the middle. I've been using the excellent 'Universal Stand Alone Filament Spool Holder' for some time with all my printers, and wanted to keep the versatility with the delta, so I remixed the universal spool holder to fit straight onto the supplied one. This allows me to easily use some of the more awkward sized reels (like Taulman 1lb reels for example), without any issues. The modified spool holder friction fits onto the existing spool mount. If you download this model to use on your T3P3 delta, please ensure you get the newer version of the adaptor, as I found that the original one I posted was too weak on the spool support rod. This is now fixed. My adapter can be left permanently installed on top of the T3P3 version as it will accept any size of spool commonly available.






The only hardware failure I've had in the last several weeks of using the Delta, was a belt slipping off the idler roller at the top of the machine. Typically, this happened three hours into a four hour print...but it was an easy fix anyway. I'm not sure why this happened - the other two look fine and it all looks pretty straight in terms of the belt travel path, however to stop it happening again, I pushed in a penny washer on the side where it was tending to slip, which seems to help. Fortunately, you can adjust the belt tension without messing up the endstop calibration, so its not really a big deal.

Checking my logs, I can see that the Delta has clocked up around ninety hours of print time, plus around another twenty hours of calibration and me mucking around with it. I think I've likely found most of the bugs now, and it seems pretty stable.





 

in terms of repeatable quality, speed and a general feeling of smug satisfaction of owning this machine, it just can't be beat. The price was spot on for all the components within the kit, and the design is flexible enough that all the extras I bought are easily achievable and I know I can mod the heck out of the design. 

I have started printing it's brother, a Kossel XL and will be using T3P3 hopefully to supply all the parts again, as I'm very impressed with the quality of their stock. The Kossel XL I'm designing is will be a dual material printer and I'm looking forward to figuring it all out - for now though, this one is a reliable and welcome addition to my bot farm.

















Taulman3D Alloy 910 - First impressions count!

posted 24 Aug 2015, 10:00 by Colin Bell


One of the materials from Taulman3D that I've been waiting for an excuse to try is their Alloy 910 line.
This material is a new for 2015 co-polymer alloy, which they boast an incredible tensile strength (8100PSI) and high durability, which is in line with all of their current range of nylon co-polymers. Being a big fan of the 645 nylon for parts which require these types of features, I've been looking for ways to 'tame the beast' - 645 is an amazing material to produce parts with, quite literally second to none in terms of strength, heat tolerance and durability, but it can be challenging to print with consistently, with warping being the key issue for my set-up.

As it happened, today I got commissioned to create some simple kitchen S-Hooks (for hanging pots and utensils from a rack), and <gasp> I've run out of 645 again. Seriously, the rate I get through this stuff is crazy, I've got through four reels of it in less than two months! Lurking in my nylon drawer was a sample pack of Alloy 910 which I had yet to try, so I decided to give it a bash on the S-Hooks.



According to the data sheet, Allloy 910 should print using the same settings that I currently use with Nylon 618, so I loaded those up - the table below shows Taulman3D's recommended settings:

Print temp = 245C - 250C
Nozzle = any size
Print speed = equivalent to ABS
Retraction = 1mm/.1mm nozzle or for a .5mm nozzle = 5mm
Print bed = Hot = Glass heated to 45C with coat of PVA
Cold = BuildTak with coat of PVA

The machine I wanted to use for this job is my Printrbot Simple Metal, which is currently configured with a heated bed covered with PEI. Normally for nylon, I would clip a Tufnol board over the top of the PEI, however I decided not to for some reason, and this proved to be a great decision, as it turned out not to be required. Alloy 910's adhesion to PEI is pretty good off the bat, however I found that due to clumping (more on that later) the part had a tendency to be caught by the nozzle and lifted off the bed, mid print.

In order to combat this, I did three things. Firstly I added a light coat of Gluestick on top of the PEI (and really it needs to be a very light coating as the Alloy 910 adheres extremely well to it. Additionally, I added a 2mm Z-lift on layer changes so that the nozzle cleared any end clumping. Finally, I set the bed temperature to 50c.

The S-Hooks I was creating needed to be strong and relatively smooth, so I sliced them for 100% infill and a 0.05mm layer height.  I printed them relatively slowly, at 20mm/s and kept retraction at my normal Nylon 618 settings of 3mm at 30mm/s.

The print process using this material at the settings I mentioned above were pretty typical of printing nylon, with a couple of exceptions. As I said, bed adhesion was no issue at all, and there was zero warp or shrinkage with this material, even in a draughty room with the air-con running - this is definitely a major plus for the Alloy 910, as most of my previously mentioned nylon material challenges are cause by warping and shrinkage in one way or another. This particular model runs the layers end to end with a very small surface area touching the bed, so was a good test of this.


Of course, nylon being nylon, some stringing is inevitable, especially between parts. Using my standard nylon retraction settings of 3mm/30mms, I still got a good amount of cobwebs between the objects on the bed. This proved extremely easy to remove though, just running a razor blade over the surface. One of the issues with cobwebbing like this is that some of it tends to get wiped up and collected on the nozzle of the hot-end, and then gets dragged over the print. Then the cobwebs clump into a charred black lump which gets deposited either at the start or end of the layer, usually in the same place each time. A Z-lift of 2mm stopped the part getting caught on the hot-end, so the print was safe, however it did leave said black lumps. In future, should retraction fine tuning not cure this (Taulman3D are recommending and additional 1mm on my current settings), I think it should be pretty easy to compensate by adding a small amount of removable support material to the sliced print job - once complete, the black lumps would come off with the support material, leaving the model intact. For the parts shown here though, I simply sliced the charred 0.5mm section off the model (after some effort, this stuff is very resilient to blades) with a razor blade. Being 100% infill, this worked well in this case.



As I said previously, Alloy910 sticks very well to PEI, and with a layer of glue stick on top of that made the part rock solid on the bed. Removal was fairly straightforward though - I just sprayed some tap water onto the parts and waited a couple of minutes for the glue to dissolve - the parts popped off the PEI after that without much issue.

After a quick clean up with a razor blade, I found the surface of the parts to be very smooth, although not as 'slippery' as with some other nylon types - 645 for example feels almost like PTFE to the touch, and 618 is almost as glossy when printed at the right temperatures. As I was printing in a 0.05mm layer height, I didn't expect much ridging, but what was there was almost completely invisible to the eye, and indeed to touch. The printed colour is a kind of pale milky white - I'll be dying these parts though, so will post on how that goes - normally I dye the line prior to printing, so this will be a new experience for me.

The parts themselves are very strong as you would expect - I tried to test to destruction on one of the parts, and found that the Alloy 910 is extremely flexible and has what I would consider to be a perfect layer bonding. I have no doubt that Taulman3D's tensile strength boasts are fully justified. It is possible to deform the part, for example, I stretched the S-Hook out into a straight line and twisted and pulled as hard as I could for some time - this didn't even really dent the model where the pliers were gripping them, and no amount of pulling would cause de-lamination. Once I let go though, the part didn't immediately spring back to its original shape, more of an elongated version. With a bit more pulling and twisting though, I was able to get it basically back into the original shape and it held that once I was done. After that bit of torture, I hung a 2.5kg pot from the s-hook and it held it without issues, only starting to deform when I upped the weight hanging from it to over 7kg. Even at 7kg I think I could have added more weight, but I decided that the hooks would be fit for purpose and stopped there. Bearing in mind the size of the small S-Hook (65mm) this is incredible.

In conclusion, I think I will place my next nylon order for Alloy 910 rather than 645 - I need to do some further testing with bridging, support and complex structures, test for machining properties like being able to drill and tap threads into it, but for now it looks like it could be a perfect replacement for 645. The ability to print on PEI and get no warp, curl or shrinkage and get all the other benefits of a strong nylon line is just too good for me not to play further with it....depending on how it handles supports and rafts, it might even be a replacement for ABS and PLA!

Sorting out the heated bed issues with flexible silicon pads

posted 6 Jun 2015, 08:52 by Colin Bell   [ updated 6 Jun 2015, 08:52 ]


I've had a love/hate relationship with my 3D printer heated beds - they are necessary for most materials, essential for others to stop model warping and aid with model adhesion to the bed during printing. On my machines they have tended to *almost* do the job. Particularly on my RepRaps, the solutions are interesting in a Heath-Robinson kind of way - they worked, but failed a lot too.  

A bit of history on my previous heater solutions and their issues.


Point in case was my original Huxley's nichrome solution - whilst doing the job remarkably well considering it's basically a toaster element sticky-taped to the bottom of a slab of metal, it caused me all kinds of grief in terms of reliability. Nichrome wire is basically impossible to solder, so connections need to be made using crimps, which is a crap solution for a moving bed - it's just going to break the connection eventually - actually quite regularly in my experience, despite my buying very expensive crimping tools and materials. 
Of course, a break is just an annoyance, and easily fixed, but it's very annoying all the same. The worst issue with this kind of set-up was short circuits - eventually the Kapton tape, heat shrink and ceramic pads which insulated the bed would go brittle under the extreme focussed heat from the Nichrome and develop a hole straight down to bare metal, leading to a short - at best this is a fire risk, and could lead to a shock I guess. I'm not sure what effect a bolt from 19v DC at 6A would have on a human (I never found out fortunately) but it would surely damage the electronics at least. Quite early on I decided to completely replace the insulation every 30-40 hours of printing just to avoid this, and fortunately it worked out for me.



Another big issue I had with this set-up was the Molex connectors used to connect the bed to the control board - whilst convenient, they regularly burned out as they are just not designed to carry the kind of current the Nichrome demands.

I eventually gave up with replacing these entirely and moved to more robust, mains rated terminal blocks, which were only marginally less convenient when I inevitably needed to get the bed off for a repair, and much more suited to the load being put onto them. 






Of course, the Nichrome wire solution was an early attempt back in the Stone-Age of RepRap to get some heat under the build platform, and things moved on pretty quickly to the now very common PCB style heaters. These are an extremely neat, tidy and safe solution and have a very low failure rate. These things work basically by shoving loads of power into a continuous serpentine shaped resistive track, which in turn expels the heat in the same way a resistor would. A lot of hot-ends use a 3W resistor as a heater, and this is the same, only on a larger scale. 

I've used PCB heaters in three of my four printers at some stage in their life, and in terms of low maintenance and reliability they cannot be beaten. 

However...there are still issues with them. The first issue is the amount of power they draw, normally something between 4 amps and 10 amps. This means that the little power brick adaptor you've been using with your printer just isn't going to cut it any more - best case is every time the bed pulls power, everything else on the printer (motors, hot-end, fans, lights) will all dim down or stop altogether until the PID loop stops the heater. This will happen repeatedly throughout the print as the bed cools and requires some power to get back up to temperature. The solution usually means butchering a beefy (300W +) ATX power supply, which can be a major undertaking for the uninitiated, although ultimately is a great cost effective solution which should be used on all 3D printers in my opinion.

The next issue with PCB heaters is that they often don't get hot enough to be properly useful. Oh they help for sure, but for example my Printrbot PCB heater topped out at around 85c when everything was running as I didn't have a chamber around the build platform, and drafts and general movement meant that it couldn't maintain higher temperatures.
It would eventually get up to 105c after around 45 minutes of being covered up and heated at full power from a 700W ATX supply, but due to the inadequate thermal design of the Printrbot bed (those F*&%#& wings!!!!) it simply couldn't sustain it, even with heavy shielding underneath. This made it effectively useless for ABS unless I put a box over the entire printer and kept all the doors and windows shut. Not ideal, as you can imagine.

Finally, the other issue I had with PCB heaters was warping of the PCB itself. On my Mendel, I had the PCB strapped down with four nuts and bolts, one at each corner of the bed frame. I noticed after several weeks use, when being heated, that the centre of the PCB would bow out from underneath the bed, losing contact with the glass. This inevitably led to a loss of heat in the middle of the bed and lots of parts popping off prematurely due to uneven heating of the surface.

So, I've tried the toaster and PCB solutions - what's next? 

Recently I decided to do a major restore and upgrade of the eMaker Huxley mentioned in the project section of this blog. The reason for this was that my son was showing an interest in 3D printing and was looking for a machine to play with. Given that I knew all the main issues with the Huxley, I wanted to ensure that all of these were fixed to save him a lot of the same frustration that I'd had. As mentioned above, that toaster Nichrome wire solution just had to go.

I'd read on forums that some RepRappers had started to adopt silicon heater pads as their bed solution, so I decided to give one of those a try.
I didn't want to spend a fortune on my experimenting with this, so decided to use the veritable AliExpress site to find the parts. Right at the top of the list on a general search came Keenovo heaters, which had some great reviews, so I decided on a 100x100mm 100W 12v unit, which should be a drop in replacement for the Nichrome solution.

The silicone heater arrived in good time (shipping was around three weeks and free) and was very well packaged. The seller also kept me informed of my order status which is a rarity when ordering direct from China in my experience, and also answered my questions in a timely manner. The device itself has a very high quality feel to it, using a good high quality rubberised fabric covering material, fabric braided and shielded (PTFE) leads and 3M 468MP adhesive already installed on the back of it. Also included and installed is a standard NTC 100K Thermistor, which is directly supported by the Marlin firmware.



Installation of the Keenovo heater was a breeze - after removing the previous Nichrome set-up, and carefully cleaning the now bare aluminium bed bottom with IPA solvent, I just peeled off the 3M adhesive backing and smoothed the heater down onto it. As I've said in previous posts, this type of adhesive is pretty permanent once applied, so I have no doubt that it will last a very long time, especially as 3M boast that it can withstand temperatures in excess of 300c, which is much higher than the Huxley will ever need. Wiring was simple - I just connected the two power leads into the bed heater terminals, and the thermistor into it's connector - job done!





The excellent quality braided leads on the Keenovo meant that cable management for the heater power and thermister where equally easy, and I didn't need to worry about them snagging or getting caught on any sharp parts due to the thick and flexible shielding.



In terms of performance, when compared to the Nichrome solution, this thing is superb. It reaches 75c from room ambient (around 21c) in less than three minutes, and stabilised there very quickly. I didn't even need to change the PID loop settings, as the stock Marlin ones worked just fine. In my testing, I found that it could maintain 125c (reaching this in around 6 minutes from ambient room temperature), which is more than adequate for ABS. 

Probing around with my Fluke IR thermometer showed that the heat spread pattern got very consistent across the entire bed after around five minutes of the reported temperature being reached, which makes sense as the aluminium bed equalises. It was most stable in the middle of the bed almost immediately, it just took a little time for the edges of the bed to catch up. Being a 150x150mm bed, and a 100x100mm sized pad, I found this to be expected and more than acceptable. Obviously, if I was doing it again for this printer, I would get a full 150x150mm pad to match the bed size properly, although it would mean some modification of the bed mounts, which might be more trouble than it's worth.

Being a 12v heater unit, and the Huxley's Sanguinololu supplying a regulated 12v for the heater circuitry, I didn't bother to upgrade the power supply for the Huxley, so it remained on its original 19v/120W power brick - yes, the fans slowed down a bit while the bed was heating, but then they did with the Nichrome solution too - I didn't notice any loss of stepper motor power or speed, and neither the Sanguinololu controller or the LCD complained or showed fault either, so clearly the power drain was within acceptable limits. I ran the bed on stress tests for several hours, concluding with a print job at 105c on a seven hour test print with no issues at all on the Keenovo or the rest of the printer and its electronics. Win!

Rather than get off-topic, I'll come back to the Huxley restore in more detail in another post, and instead move to the next printer which required an improved bed solution, the Printrbot Simple Metal.

After being inspired by Thomas Sanladerer's excellent video on Silicon heaters & Solid State Relays I decided to take the plunge and do a proper solution for my favourite production printer. Since I'd had such success with the Huxley using the Keenoovo products, I decided to go straight to them and ask for their advice. I wanted to have a mains powered unit, which fitted the Printrbot and had way more power than the then current PCB solution. My main issues where that I had to remember to pre-heat the bed, often for 45 minutes prior to actually starting printing, and if I had a failure and needed to restart, I'd have to wait all over again before the job was finally going again - this pet peeve was my main reason for this rather epic upgrade path.


Keenovo's recommendation was a 220v, 500W flexible heater pad, which I thought was going to be way overkill for my little Printrbot - I wasn't wrong there, it is overkill, but it certainly does an admirable job...read on.

The pad I selected is 150x150mm, which is a drop in replacement for the Printrbot PCB heater. As with the previous heater, this has a high quality, durable feel to it, sporting the same flame resistant rubberised fabric covering, PTFE insulated leads with a metal braided sleeving. Also installed is the 3M 468MP adhesive, and internal thermal fuses and an NTC 100k thermistor. The specifications also state that this unit can sustain temperatures up to 260c, which is way more than I will need.

In the picture to the left, you can see that I've prepared the bottom of the bed with a single Kapton sheet covering over any exposed aluminium. The silicon pad is just resting in the hole where it will eventually live, while I tested the wiring and ensure that the pad was working.




A word of warning here...while it's a good idea to test components before the final installation, you need to be aware that on heater pads of this kind of power, the backing sheet for the adhesive is definitely not heat proof like the adhesive it's protecting. As you can see, even with a short test of less than three minutes at around 80c, the backing sheet scorched. 









Of course, you're going to be peeling this off anyway, so you might think this isn't a big deal, however, I needed to spend quite a while picking tiny pieces of charred paper off the adhesive with a razor blade, which was a pain. As you can see, I managed to damage the adhesive layer whilst doing this, so rather than take a chance with a mains powered heater falling off the bed, I put another sheet of 3M 468MP onto the bottom of the bed for additional insurance.








The final touch I added is a metallic heat shield (not supplied!) which is Kapton taped directly onto the pad. This is more about protecting the electronics on the printer which sit directly below the bed than bed insulation. This shield, along with the fans installed under the chassis, keep the electronics at around 35c when the bed is running hot. 



Keenovo also supplied a Fotek Solid State Relay (SSR-40-DA) for use with the bed - it should be noted that this wasn't part of the silicon pad purchase, they included it when I enquired as to which type of SSR was recommended. I had an aluminium heatsink left over from a previous job, so bolted the SSR directly onto it. Now, it has to be said - in this application, the heatsink is not required at all - the SSR runs very cool, barely even going over ambient temperature, even under heavy loads. It's also completely silent in operation, the only way you know it's working is when the red status LED on the SSR lights to say it's receiving a pulse from the printer's electronics to engage the bed heater.

Wiring the SSR and heater pad are very straightforward, and I just followed Thomas Sanladerer's video guide. In summary, here is the wiring diagram:

SSR Wiring

(Click on the image to enlarge it)

After butchering a couple of standard mains PC cables, I was able to make all the necessary connections, just using mains rated terminal blocks as appropriate.


The final installation is fairly tidy, and I concluded by taping over all the contacts. 

Now, in operation, this monster solution has exceeded all of my expectations and I think I can say I'm finally satisfied with the heated bed solution on my Printrbot. 



No longer do I need to wait for the bed to get up to temperature, no longer do I need to worry about a draft causing the model to pop off the bed prematurely, no longer do I need to worry about the power being sapped by inefficient thermal bed design - this thing is so powerful it just ignores all of these issues.

It gets from room ambient (around 21c) to 70c in...wait for it...26 seconds!
It gets from room ambient (around 21c) to 120c in... 1 minute 8 seconds!

Hell yeah.


Now, as you can see from the monitor graph above, the PID loop in Marlin needs some dialling in - it heats so ferociously that its overshooting by around 12c on every heat cycle before the PID loop realises and switches it off, giving the sawtooth heating pattern seen in the graph. Also, the pad heats much faster than the aluminium bed, meaning that those crazy fast heating times above are a little misleading. What I'm finding now is that I still need to wait a couple of minutes for the bed surface to equalise the temperature. Additionally, I've noticed that the discrepancy between what Marlin reports as the current temperature, and what is actual on the bed surface is exaggerated by around 10c (so if Marlin thinks its 50c, the surface is actually 40c). 

These issues are simply software fine tuning though, and not a real issue in the long term. Once I figure out the PID loop code in Marlin I'll do a follow up post to explain what I changed.

Winner, winner, chicken dinner indeed.




My Designs

posted 5 Jun 2015, 12:51 by Colin Bell


For those asking, all my designs go up to Thingiverse here.

Yeah I know...a lot of people don't like Thingiverse and have migrated away to YouMagine instead, but honestly, I haven't had a lot of luck with that site so far, and it's been unresolvable for me more times than I care to mention. However, I do have a profile on there, and all my designs to get uploaded there too, when I remember to sync them up and can actually get on there... My profile on Youmagine is here.


PEI. Its Magical. Kinda.

posted 2 May 2015, 05:34 by Colin Bell   [ updated 3 May 2015, 15:27 ]



One of the best upgrades I've recently made to my Printrbot is the addition of a PEI sheet as bed material. I’d been reading about the lucky Taz mini users that get this as part of the standard kit, and their claims of it’s almost magical qualities in terms of material adhesion whilst printing, and ease of release when the job completes. I must admit I was a bit sceptical at first, but was getting sick of all the glue and copious amounts of very expensive Kapton tape I was getting through, especially when using ABS.
 
I secured a 12”x12” sheet of Ultim PEI at a 0.04” thickness (that’s 300x300x1.016mm) from Amazon, which was pretty reasonably priced at under $30. The only issue I had with this was that it doesn't ship outside of the US, but fortunately a friend of mine was travelling over, so I had it delivered to him. There are several resellers on Amazon, all who seem to be in North America, and only a couple will ship to Europe at the usual extortionate prices, so shop around. The other thing to watch is the imperial measurements…I actually ordered a piece which was 22mm thick at first before I noticed that there wasn't a decimal point in the place I thought it should be…
 
The sheet that finally arrived was perfectly square and had no marks on it at all due to excellent packaging and the fact that both side were protected with a thin plastic film. One side of the sheet is smooth and flat and the other has a slight texture. It doesn’t actually make any difference to prints which side you have facing up – the smooth obviously gives a nice glass like finish to the bottom of prints, and the texture side *may* give slightly better adhesion to larger prints. My testing on this was inconclusive though, as it seems that even bed temperature actually plays a much more important role in the model adhesion that anything else.
 
Given that the sheet I bought was just over 1mm thick, it is very flexible and easily can be bent. It’s not easy to break though, and would require a lot of force to shatter or cause a tear due to flexing – way more than I was prepared to try anyway. The sheet can be cut easily to shape and size, and I achieved this by scoring repeatedly with a craft knife and finally cutting along the score with some very sharp kitchen scissors. During the cutting I had no issues with flaking, cracks or small shards appearing – it cut very cleanly.
 
I decided to cut the sheet into four 150x150mm squares as I have two printers with that size bed. This means I have a spare surface for each machine should the PEI start to wear down (although in retrospect I think the PEI will outlast most of the electronics…)


 
Deciding how to mount it on the bed was a bit of a challenge, as I wanted some versatility in terms of changing surfaces, for example using Tufnol for Nylon printing. In the end though, given how thin it is I went ahead on both machines and stuck it directly onto the aluminium beds using good ol’ 3M468MP transfer tape, which I also bought in 300x300 sheets from Amazon. I simply cut it to size, cleaned the bed with a mild soap solution followed by a polish with an IPA aerosol solvent, and then smoothed the tape down with a stiff card. The adhesive has removable backings on both sides so this is an easy job. Once the top backing is removed though, be very careful not to let the PEI touch the sticky part of the tape until you have it positioned correctly…getting it unstuck is possible, but much harder than you might anticipate and you could end up partially removing the tape from the bed if you’re not careful. I found that the glue used on both sides of the 468MP tape takes a while to set fully (about 30 minutes from exposure to air it seems). Once it is set though, it makes for an incredibly strong bond and you can be 100% confident that you won’t be experiencing any lifting of the PEI or the tape from the bed. Once I had the PEI mounted, I carefully rubbed it down with a soft cloth to remove any tiny air bubbles – this has worked extremely well.
 
So, that’s the fitting done – how does it perform?
 
Well, it’s magical.
 
Almost.
 
As I mentioned earlier, bed temperature is the key to using this stuff effectively. Now, I don’t just mean heat it up and away you go – that’ll work in the middle of the bed where the heat is most stable, but not around the edges of the bed – so if you’re printing something large you need to take some extra time to check your bed is evenly heated, which in my case meant changing the bed heater to a higher output silicon version than the stock Nichrome heater I’d been using on one of the printers. Not ensuring even heating for larger objects will result in the dreaded curling and potential print failures we are all familiar with.
 
Now saying that, once you get the bed heating nicely, you can really start to enjoy the benefits of this material. It’s virtually maintenance and preparation free – the only maintenance you’ll need to do is to give it a wipe with IPA before every print. The PEI surface is quite resilient to marking, so as long as you take care not to gouge it if you have to pry up some rock solid PLA with a blade for example, you shouldn't have issues with surface marking.
 
With PLA, I’ve found that a bed temperature of 70c is ideal, even for 100% infill 150x150mm sized prints. No movement, no warping – perfect adhesion. Magical. Except it’s a bit too magical with its adhesion to PLA sometimes and you may have to carefully get a craft knife under a corner of the model to remove it. On the good side though, as soon as you lift even the smallest part of the model, the rest just pops off the bed most of the time – I have yet to really struggle to get a part of the bed made in PLA.










 
For ABS, the PEI needs plenty of heat in order for its magic to work – the best temperature I’ve found is a consistent 100c throughout the print – providing the bed is heated evenly, it will stick and not curl or warp. Here’s where it gets really magical though – to get ABS off the bed just let it cool down to under 40c and the part usually just pops off. If you’re impatient though, a quick blast with a freeze spray (or an inverted air duster) makes it virtually leap off the bed. It’s worth printing in ABS just to do this!

I have found that on very large solid prints (over 60mm base with 4 bottom layers and greater than 40% infill for example) the adhesion magic ends and a thin coat of gluestick is the only option to stop warping. In my particular case, drafts are a big enemy too - my Printrbot sits next to a door, and every time the door opened I was getting loss of adhesion from the model. Gluestick did help enormously in this case though. Must get around to building that bed enclosure.

Again, the PEI is easy to clean when using Gluestick - the gluestick is water soluble, so I just spray water onto the glue, let it sit for a minute and wipe it off with a paper towel. A quick quirt of IPA and a polish and it's ready for action again. 

In conclusion, with ABS, PEI isn't magical. But...and this is a big but...its a lot easier to deal with than Kapton tape and glue. For smaller objects, no glue is definitely an option, and often a brim isn't even required. I've had better success with ABS models since installing the PEI and this is a win for me. Do pay attention to even and consistent heating of the bed though - for ABS you want a bed temperature of at least 90c, and preferably 105c across the entire surface where the model touches it.

For PLA, the PEI material is wonderful and the bed requires zero preparation or clean-up (other than the obligatory IPA wipe to get rid of fingerprint grease). If you only use PLA for printing, you'll wonder what you ever did without it, as the lower maintenance and increase success rate of prints will save you hours of frustration.

This weekend I intend to try out some other materials including Nylon printing on the PEI, although I'm not expecting too much success there as Nylon seems to like a fibrous surface to stick too like Tufnol. I also have some Flexible materials and PCTPE, along with some Laywood to try. 


Taulman 645 - bridging capabilities

posted 22 Feb 2015, 03:29 by Colin Bell


I've been playing with Taulman 645 again to make several industrial strength parts and wanted to just highlight the incredible bridging capabilities of this material.

Whilst printing a measuring jug which required a minimum of support (quite important in a material of this strength as removing support material can be challenging...) the very thin supports that I'd defined broke free of the bed mid-print, and sagged towards the body of the jug. In virtually any other material this would be the end of the print, resulting in a bunch of spaghetti to clean up. Using 645 though, you can see that the material found the tiniest of purchase on what remained of the support and continued to build up - which is just amazing! Admittedly, the support structure isn't pretty, but it did result in a successful print, despite the support almost failing!



















In this picture to the left, you can see that the handle actually fell off the support at the back of the jug. Fortunately, this happened just as the main body of the handle had finished printing (top heavy I guess) so I just let the print continue, as the support for the top of the handles curve was intact and holding.

Now glueing nylon is very challenging, as most solvents and glues won't touch it. The best method I've found is to use a hot air gun that I normally use for soldering SMD components. I set the air flow to high, and the temperature at 245c and evenly heated the surface to be welded after first trimming it down flat with a knife. The best time to join parts seems to be when the surface goes shiny and looks like its just about to turn liquid (not very scientific, I know). I just jammed the two parts together at this point, held for about 45 seconds and then left it to cool. This very effectively joined the parts, and the join seems just as strong as the rest of the print.


















I can't get over strength of this material though, I recently used it to make a sliding latch for my balcony door, and it's super strong, whilst still being flexible enough that tolerances on measurements just cease to be an issue in this kind of application. The ability to be able to drill and tap into this material also makes it very flexible for quick parts manufacturing. My only issue now is I've run out, and it's impossible to buy anywhere locally. Ah, well, I'll try some other material instead!




Printrbot Simple Metal's Heated bed

posted 14 Feb 2015, 14:11 by Colin Bell   [ updated 14 Feb 2015, 14:16 ]



This is the first of an irregular series of posts focussing around the servicing and maintenance of the Printrbot Simple Metal.

One of the recent upgrades I made to my printer is the heated bed kit. This consists of new 'wings' for the build platform, a PCB heater, some wiring and a nice milled aluminium build platform.

I won't bother going through the installation here - it's very simple and well documented on the Printrbot web site.






Before I even fired it up for the first time, I knew it wasn't going to be the perfect solution I was hoping for. Whilst it does work, and very reliably at that - it simply isn't deigned well enough for high temperature printing. Most materials appreciate a bit of warmth underneath to help with reducing warping etc, ABS in particular demands a consistent bed temperature of between 105c and 110c unless you're using copious amounts of glue or a PEI material on the build platform. Whilst I'm no expert on thermal design, I can see that no insulation underneath is a problem, and those wings...they're basically giant frickin' heatsinks to warm up my room. All in all about as efficient as a fart in a thunderstorm.


With just the stock kit installed, the bed took around twenty minutes to get to 85c and any setting higher than that took in the order of five to eight minutes per degree increase. For PLA, this was fine - it got up to 60c from room temperature (about 22c) in around ten minutes, which was slow but acceptable. As I'd recently upgraded my power supply to a beefy ATX2 capable of supplying 25A on the 12v rail, I'm pretty sure I'm pushing enough power through it. So...the problem is likely elsewhere.

Looking at the old RepRap Huxley on the shelf, which uses a Nichrome wire system on its bed, I can see that it has an automotive exhaust heat shield over the Nichrome. Also, knowing that PCBs are not great insulators, I thought this would be a good place to start. I taped the shield centrally over the heater PCB with good old Kapton tape (where would I be without that stuff?) and made sure to insulate wiring and screw heads etc to reduce any electrical short risk.

Initial tests with this saw the bed temperature shooting up to 104c in around 27 minutes. Compared to it's previous maximum of 85c, this is a win!


Now for the wings - these are kind of necessary to hold the bed drive belt in place, so losing them isn't an option without some serious modification of the structure of the bed. Which might come later.

For now though, I wanted to try and get some insulation between the aluminium bed and the wings, in the hopes of reducing the thermal losses I'm getting from them. I know they get extremely hot normally, and I've measured them at around 80c after around 40 minutes of the bed running at 85c. All this heat is just going to waste, and it's an additional burn risk to boot.

I had some very high density foam left over from some device packaging, which I put a piece of in the oven at 250c for an hour to see if it would survive. Not only did it survive, but it seemed just as springy and did not warp, scorch or burn. I'd love to find out exactly what it is, as I think it would be handy for a number of things.


I cut four lengths of this about 2mm thick to sit between the wings and the build plate and screwed it down nice and tight, squashing the foam in place.

The difference with these installed is good and bad...heating is now a bit quicker than it was, but not dramatically so. It can now go from room temperature to 60c in 3 minutes flat, but the rise to 110 still took 32 minutes in total. But it does now get to 110c and maintain it! The rise times seem to slow down from around 70c upwards.

The bad...those bloody wings are still getting hot over time. The foam seems to have slowed this a bit, but the heat is still creeping over. Now, with the bed reading at 95c, the wings are still sitting around 67c, which is not as good as I'd hoped.

In terms of use though, what I've found has helped a lot with heating times, is to ensure that all the fans are off (doh...) and also to cover the top of the build plate with a biscuit tin cover until it's done heating. This can knock 10-12 minutes of the total heat-up time.

Once the machine starts printing, I've been using a bed temperature 110c for the first 3 layers, and 95 for the remainder. Of course, the surface of the bed isn't as high as the 
thermistor reading - in fact it's around 10c lower I'm observing. Covering all exposed areas of the aluminium bed has further improved stability over time, I'm seeing the bed kick on at the same frequency to maintain temperatures, but for a lower amount of time. 

Tomorrow I will get some adhesive pipe insulation tape and cover everything with that - it can't hurt and it's a cheap test.

I had hoped that all this effort might mitigate the need for glue on large parts, but even as I'm writing this, I just had a failure due to warping three hours into the job....out with the glue stick again!





Nylon bed adhesion

posted 7 Feb 2015, 07:39 by Colin Bell   [ updated 7 Feb 2015, 07:41 ]


I've done a fair bit of printing in nylon recently, using Taulman3D's 618 material. I've had pretty good success in the past with using my favourite combination of a cold bed covered in Kapton tape and glue stick, and had virtually no bed adhesion issues with single walled prints, even large ones. I have noticed though that when you combine a large print with multiple layers, you still get some corner warping and I had several failed jobs due to this. 

I remembered reading on RichRap's blog a long time ago that Tufnol was a good solution for Nylon based products and grabbed a couple of sheets of it ages ago. Tufnol is a cellulose and resin product which is compressed into very flat, flexible sheets. Its also very tough so can take the high temperatures required for Nylon printing, along with some bending to remove well stuck parts from it. The reason I hadn't used it thus far was because I couldn't figure out a reliable way to have the Printrbot perform it's auto-bed level routine with the inductive probe. I'd tried a couple of solutions in the past using aluminium baking foil on the probe landing spots, but this proved to be very unreliable.

One of my most recent jobs is to create a bunch of ID pass holders with some branding for my team - I wanted these to be tough and flexible, and I needed to create around 10 in total, and was having issues keeping the things stuck down due to the 4 bottom layers warping a lifting off the bed before the prints completed. This was getting very annoying and I was only averaging one in every five attempts being successful, which is just a waste of time and materials.

So, I decided to give Tufnol another try. I cut down a sheet to the size of the PBSM bed with a craft knife by scoring it repeatedly until I could break off the excess material. Securing it down with binder clips (I used six in the end) keeps it nice and stable and flattens out any curving in the surface.
The only issue with the binder clips is that very occasionally if I don't check the hot ends path prior to the print, it will pass over the end of the clip and snag. I've learned to review the tool path prior to prints for this reason now, and remove any clip that might get in the way.

As I mentioned previously, I needed to find a solution to allow the inductive bed levelling probe to work. Aluminium foil kind of worked, but not reliably enough to trust. I tried folding it into squares and even pasted the entire bottom of the Tufnol with the stuff, but gave up after a couple of homing disasters.

So, more density required for the metal on the landing areas, but still flat and thin enough that the hot end won't catch on it and rip it off. 
After several failed tests with coins, copper clad PCB and other bits of metallic junk I had laying around, I ended up cutting several strips support material from a reel of Molex pins that I had in my spares draw. Once the pins are removed, the thin tin covered copper strip is normally discarded, however I found that this is just the right density to trigger the inductive probe reliably. By running a very slow G29 command on the printer, I was able to line up a couple of 1cm strips side by side at each of the landing points, which I then glued down onto the board in the pattern you see in the pictures. This has proven to be very reliable.

The next step was ensuring that the Nylon stuck to the Tufnol. Again, on small thin prints of only one or two bottom layers I had no issues either keeping the model on the bed, or removing it afterwards, however my ID passes were still contracting and warping, even though the Tufnol offers excellent adhesion.

So, back to the glue stick again. I've found that a fresh and liberal coat stops any warping whatsoever, even with one test which covered the whole 150x150mm bed with several layers of nylon. Of course, removing the object now requires a craft knife (an Exacto for all the US readers) but providing it's done carefully, the models come off intact. Being water soluble, the glue stick residue comes off the bottom of the model under a tap. 

I've found the most reliable method for printing in this way requires the Tufnol to be washed and fresh glue stick to be added for each print. This literally takes two minutes, and I just spray a small amount of water on the glue, and scrub it off with a
kitchen 
scrubbing cloth. A quick wipe down with IPA solvent after that and it's ready to go again.

I also had to play with my probe offsets for the G29, and ended up going with a -0.8mm setting - normally when printing directly onto the heated bed, I'd been using -0.7mm, but this was giving a bit of a 'smashed' look to the first layer. 














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