Mechanics and Construction > Mechanics and Construction

My homebrew CNC

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vinito:
I set everything up and tuned the motors the best I can. It's just not performing very well.
The videos I've seen of Mach3 running steppers through a G540 all show pretty smooth and solid motion. Some are even pretty fast. Mine are pretty awful, though better than with the cheap Chinese driver.

We'll see if there is any improvement with the new PC. Better performance is likely but I suspect my motors, which are the smallest NEMA23 frame I've ever found, are simply not well-suited for this kind of task.

If anyone has experience with this kind of stuff and can recommend a good motor to work with Mach3 and the Gecko, please let me know. There has to be a way to get this thing running right. I'm shooting for reliable, smooth, fast motion (in that order) and it seems like I should be able to get it with the Gecko.

Thanks for any advice.

Edit to add:
I set up a desktop box and got no better performance, then I discovered that the bad-performing motors both had one wire come loose from the terminal block I installed under the table. Uugh. I fretted about it all day, got confused and frustrated, and the fix was a simple snugging up of two lost connections. So the good news is that all three axes are now fast, smooth and torquey. Tons better than before. I think this machine might be worth having around after all.

vinito:
Wow the Gecko is working great. With the Chinese driver I could get max feedrates of 13 IPM on the table and 4 IPM on Z. Now I am repeatably getting 40 IPM on all axes, which maxes out the Mach3 kernel so may get even faster if I can jack the kernel higher with the new system.

Here's a short video:
CNC machine Mach3 and G540

vinito:
Made a bit more progress.
If you watch the video, you will see that above the spindle there is a bracket holding nothing. I made that to hold a dremel and at first it was mounted at the bottom of the Z-axis plate thing. After I made the new spindle and found that the motor I intended to use on it was waaay too wimpy to work on it, I re-thought and decided to modify the dremel bracket and move it to the top so maybe it could drive the spindle. So I hooked the dremel back up and connected it to the spindle with a coupler and tried it out last night. There is some vibration, which is worse at some speeds than others so I just have to fiddle and get between the harmonic nodes. But it does work OK. I was afraid that the bearings would just burn up at those kind of speeds, but it ran for 20 minutes or so last night at about 20-25K rpm and it hardly got warm. A pleasant surprise.

I went a little further and milled flat a piece of plastic to true the table up to the axes and that worked like a champ. I can tape copper clad to the now flat plastic and etch PCBs. I'll be giving that a try this weekend.

Also got the new system built and installed. It's a sweet-running little thing and I've been able to ramp the rapids up to 50 inches per minute. Since I'm only driving my motors at 25 - any faster than that and it loses torque and skips. I'm happy with that. 50ipm is so much faster than I had before that I have no plans to increase the power supply voltage just to get a bit faster rapids out of it. And of course the new system is just generally tons smoother and faster than that relic I had it running on before.

Once I get it etching some PCBs I'll make another small video and link to it.

Getting pretty close now.

vinito:
I finally milled my first usable PCB with my little machine.
It's not perfect, but it would be functional. You'd just have to be a little more careful with the soldering I think.

The method I used to flip the board to mill side 2 was fairly simple. I just drilled holes of a proper diameter to fit a couple small pins I had at 0,0 and 3,0. On this board, the way it was laid out on Eagle had the origin (0,0) slightly off the board outline, so the registration holes will be gone once the board is cut off the material. You could use any two holes, but using the origin for one of them is handy and quick way to get things set up for the flip.

I'm very pleased with the motion of the machine, but the spindle still leaves something to be desired. So I'll be doing something different eventually.

I'm not sure how this occurred, but you can see that the registration kind of got spread out from one side of the board to the other along the X-axis. The motors didn't skip steps, it's just off in the code for some reason. I'll probably try some other method of generating the code and see if I can fix that. The PCB-GCODE thing is a bit awkward to use anyway, so maybe the next thing I try will be better anyway.

Side 1:


Side 2:


Here's a short video of the machine making the board this morning. There is no sound on purpose - it's just an annoying whining sound from the noisy spindle, and the sound and video got progressively out of sync as the video progressed for some reason, so I just left it out:

http://youtu.be/XUPwQjAMokE

By the way...
The machine is successfully rapid positioning at 60 inches per minute but I have it ramped to keep things solid, so it takes about an inch of motion to get up to full speed. I can probably reduce the ramp time, but the long side of milling on this board was only 8-1/2 minutes. Not bad.

vinito:
Well OK. I finally got my little machine working pretty well. Yaaaaay!!!

I bought a fairly inexpensive spindle off eBay. As far as I know, they are kind of new on the scene. I've seen them before, but not common and not on eBay, though it could be that I just wasn't using the correct search string. At any rate, the spindle spins about 1K to 30K rpm as per the specs and the runout is very small (less than .0005"). It is very quiet as well - MUCH quieter than a router motor and even quieter than a Dremel by probably 3 or 4 times. You just hear a whoosh and little hum. It's pretty torquey too even at low RPM. It takes an ER collet like the one I built, but it's the next size larger (ER11 rather than ER8) and will accept up to 5/16" diameter shanks if I ever have a need for it. I won't on this machine, but that's the capacity anyway.

I wired a relay in to switch it on and off from Mach3 and plan to eventually have Mach control the RPM as well. It's pretty nice just to be able to let Mach turn it on and off - seems more professional or something. For now a simple 5K potentiometer controls the RPM. Another nice thing is that it comes up to speed in probably a quarter of a second, so no delay/wait necessary in the programming.

I did a little testing then ran the same board I did before. The results are dramatically better. I haven't figured out how to take a good picture of a PC board yet, but following is a picture of the spindle and the results of the routing. Hard to see (can't see it?) but the result is very, very clean and crisp. It's just tons better than before and I'm happy the long-awaited good performance is finally here. Looking forward to being able to actually do some good work on it.



Yesterday's new routing on top. Old routing (from before) on bottom.
Same exact code, cutter and depth as before. The old routing cut so much wider because of the runout. That was with my home-made spindle too, meaning a Dremel performs even worse.


That new little spindle is a nice setup for a reasonable price and I highly recommend it if you have a similar project. Search "300 watt spindle" under Business and Industrial on eBay and you'll find them there (with various options, i.e. with mounting bracket, with PWM speed control, with power supply, etc.).

Or here's a source in the US who sells them for a little higher price for the same thing: link. This source also carries a good selection of other pretty nice stuff for decent prices. Interesting source. Their home page

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