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. 

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

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. 

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).

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.

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.

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. 

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!

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.

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.

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.