CNC Mill >
Well, kinda. The CAD is getting done. There are still a lot of screwholes to put in (plus some other little details to work out, like not having leadscrews magically go through bricks of aluminum), but it's looking good overall. After that, it's a run past a real MechE, getting a whole lot of metal and screws, and then some quality time machining parts.
(I also got some new couplers to connect the leadscrews to my steppers, but those aren't quite as exciting)
I need to secure the ballscrews somehow, and that means bearings. [Un]Fortunately, the ballscrews aren't the same size as my existing leadscrews, meaning I need new bearings. And that lead to a whole new can of worms, namely "what kind of bearings?"Long story short, it looks like they don't make spherical roller bearings small enough, so I just went with some angular contact bearings. Those seemed to be decent for both axial and radial loads, though I imagine only the former is really relevant, and only marginally at that. With the loads this thing is likely to see, I suspect regular ball bearing would have been good enough. I figured if I was going to the effort of putting ballscrews on, I might as well at least mount them with nice bearings.
Well, that happened. I got trained in on the CNC mill at work, and they talked about having ballscrews and how great they were. So... I got jealous and decided my mill needed them as well. If I'm upgrading the thing, I might as well do it right. Plus it's incentive to actually work on it, though actually being able to use the mill at work to fabricate the pieces is also a huge help.
I finally decided that enough was enough, and added real depth probing to my CNC mill. The BeagleBone has plenty of inputs to support it (I even have a spare with a pull-up resistor pre-soldered), and since copper-clad board is conductive (along with my spindle and tools), it was really easy to add a few wires, tweak the configuration, and have it working.
So now I can tell the machine to depth-probe a chunk of copper-clad board, then compensate the PCB's milling depth based on those heights. This isn't entirely automatic (you need to run the depth-probing gcode, then run a converter script to modify your gcode, THEN run the PCB milling gcode), but it's pretty painless. And the results are pretty darn good- I just milled a board, and things overall appear to be pretty darn even. There was one edge that seems to be cut too shallow, though. Maybe an aluminum chip got under there or something... there are certainly enough of them around.
I even improved my code to be slightly more flexible, and stuck it up on Github in case somebody stumbles on this page and finds it useful.
There would be pictures here but all there is to see is a couple of wires, which I didn't deem worthy of an image.
Keywords to help people find this: PCB milling, depth probing, depth compensation, linuxcnc
Big news... big chunks of aluminum! I finally got the plates (and channel... and other chunks) needed to upgrade my machine yet again. The plates are 3/8", which I think should be enough to eliminate vibrations and resist bending. They certainly FEEL hefty enough.
Anyway, the big pieces will form the base, sides, and back of the updated machine, while the channel you can see buried under the long thin pieces will be the gantry. Those smaller pieces are to be basically the glue to hold everything together.
Now I just need to get back into the shop with the big mill for several hours.
I finished installing the Gecko Drives, and my CNC mill is back up and running. As usual, I'd also say it's better than ever.
Two upgrades (since it was last running) make it better: First, it's now being controlled by a BeagleBone Black, which means real real-time stepping thanks to a dedicated real-time unit. No more software jitter! Less notable, but still exciting features are the use of a recent OS (Debian 7.4 instead of Ubuntu 10.04) and lower power consumption. No idea how relevant the PC's consumption was in light of the multiple amps going through the steppers, but now it's under 10 watts (for the computer, at any rate).
The second improvement is the stepper drivers. The Gecko Drives are so much better (at least in the 5 minutes of testing/playing I've done) than the previous cheapo board I was using! They have improved resolution (nominally, at least; 10 microsteps per full step vs 2 for the old board) and run quieter, smoother, and faster. Plus they hopefully won't blow up. I think they're worth the investment.
To aid them in not blowing up, I've "borrowed" a heatsink from an old Pentium II CPU. It's the perfect size to attach all three Geckos and should provide more than adequate heatsinking, especially since I'm running the drivers below the current specified as requiring additional heatsinking. Better to be safe than have another (much more expensive) driver blow up!
Pictures will show up whenever I get my hands on a decent camera.
My stepper driver board's Y axis had a little issue... it exploded:
I can't say I even know what went wrong (I wasn't even milling at the time- just testing out using a BeagleBone Black to drive the signals). My steppers seem OK, though, so I'm assuming that it's a case of "buy cheap stuff, and it'll blow up". I'm sure that's a thing. In any case, I've got some Gecko Drives that I'm getting installed (pictures... sometime). Hopefully they'll be overall better. And not explode.
I had to do a revision of the "mystery board" from last week, so I made a video. As before, this video is pretty poor quality, since the camera refuses to focus properly.
The biggest thing to see in the video is the speed at which milling can be done- 13 inches/minute in this case. It could probably go faster, but I haven't tried that yet.
I still have some aluminum milling to do, but need to finish up the GCode for that before I can act on it.
For my definition of "better", at any rate.
Firstly, the mill is assembled again! Assembled is generally better than disassembled.
Also, the new X axis leadscrew is finally installed, and the stepper mounted. Better still, they're exceedingly close to perfectly aligned. This is thanks in part to the little piece of angle aluminum with the green screws through it. It was much easier to get things aligned when referencing to the plane that the screw is already in. It's not the thickest of materials, but the screws don't tend to see much load in my applications, so it should be fine. In any case, it should be easy to reinforce should the need arise.
Also, having a tool perpendicular to the workpiece is generally considered "better" (unless you have more axes, I suppose). I've done some more work on getting everything as perpendicular as possible (I've already noted my work on getting the Z axis slide perpendicular; this time I adjusted the spindle mount on the slide), with some pleasing results:
Despite the swirls you can see in the images above, the result is incredibly smooth. There's a little swarf on there yet, but no ridges I can feel due to misalignment. Better still, the tooling marks seem consistent around the whole circle, meaning the tool probably isn't off-kilter, and thus digging in on one side or the other (as can be seen in previous operations).
There are two other things to see in the pictures above. Firstly, that the circles aren't concentric like you might expect. This was due mostly to my laziness. You can see in the image on the right that the workpiece is only clamped down on one side... not conducive to staying in place, especially when tearing into aluminum at 20 inches/minute. Cutting around the circles was fine, but each cut inward to start the next pass moved the workpiece a bit. The other thing to notice is the snazzy new 1/4" end mill. I finally got a 1/4" collet, and obviously had to have an end mill to go with it. It certainly makes the chips fly... I really need a skirt around the toolhead or something. In any case, it works quite well.
That's all I've got. you would think I would have gotten more done over an entire week (spring break) than that, but getting things aligned is a painstaking process. And, of course, it just wouldn't be spring break without homework to do. I did have a video of the cuts shown above, but lost it. That'll teach me for being overly-zealous in keeping the camera memory card clean and saving things to /tmp... I'm sure there will be more opportunities in the future.
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