New MPCNC build near Chicago

I have a working MPCNC build! I’d like to express my thanks to Ryan and everyone on these forums, which I consulted constantly throughout the build. I bought the hardware kit (sans electronics) from here but used a Mega and RAMPS1.4 board from Aliexpress I had sitting around. I am running the Marlin firmware and Octoprint running on a Pi as a host. I’m using A4988 Pololu driver boards which only support 1/16 steps, so I had to recompile the firmware after setting the value for DEFAULT_AXIS_STEPS_PER_UNIT to {100, 100, 400, 100} in Configuration.h. I’m using a dual-endstop setup. Working volume is 24 x 24 x 5.5. I use Fusion with the guffy postproccessor.

Some adventures I had:

  • The first time I plugged in the Mega/RAMPS board, I was greeted with grey smoke. I made the mistake of not checking the pin-outs on the stepper driver boards, and plugged all five of them in backwards, so all 5 were destroyed instantly.
  • This also burned up the 5V regulator on the Mega. After replacing the regulator and stepper drivers, the Mega still works.
  • I printed everything with PETG out of habit since that's what I commonly use. I think this has resulted in a gantry assembly that flexes more than it would with PLA. I'm going to try reprinting those parts with PLA to see what happens.
  • The arm on one of my endstops fell off without me noticing, leading to a very exciting homing process featuring lots of grinding and clunking. I probably should have expected that from a $0.50 endstop switch. I will upgrade to better ones.
  • I know, it's too tall. I'm going to shorten it. I don't ever plan on using it as a 3D printer.
  • Movements weren't initially that smooth owing to the rough coating on the conduit. It has already started to wear smoother in some spots. I plan to run it in big squares for a while to wear the rails in.
  • I over tightened all the bearings. Listen to Ryan when he says not to do that. I loosened everything up.
  • I initially had some random Z plunges into the work piece, even though speeds and feeds were well below the maximums. I lowered my Z current limit in the stepper driver and moved the spindle power cord away from the stepper wires. It hasn't happened again. I also tune my tool paths in fusions to eliminate all the Z movements during adaptive clearing of a pocket.
  • I also had missed steps on Y in my initial runs. My steppers were extremely hot (defined as "can only hold hand on it for 10 seconds before pulling away") so I lowered all the current limits and haven't had that problem again since. The steppers are now warm but not hot.
  • I have significant stretch in the belts due to the zip ties. I'm not convinced it matters given the good results I'm getting.
Here's a picture of the MPCNC and my first wood milling results (after solving my stepper issues)... it exceeded my expectations given how much flex there is in my build, and the $1 endmill I was using.

Hopefully this wasn’t too wordy. Thanks Ryan for all of this awesomeness!






Nice to see another build in the Chicago area.

The part you cust looks really good.

Nice piece! Did you run into any issues with the knots?

Well heck, you are basically a CNC pro at this point. You hit every problem you could have.


Welcome to the crew!

The knots didn’t cause a problem. That was meant to be a test piece so I did’t put effort into making sure the stock was clean.

On the finishing pass some sort of tiny little bug crawled out and sat on the edge, watching the rest of the milling process.

OK, so your next project is obviously to design and cut the bleacher seats for the bug stadium. :slight_smile:

1 Like

Here’s an update.

PLA vs PETG - I re-printed the gantry parts in PLA, but this didn’t result in any apparent reduction in flex. I unscientifically just kind of grabbed the chuck with the steppers energized and pushed it around to see how much deflection occurred. Answer: a lot.

My zip ties allowed the belts to “stretch” quite a bit so I printed this belt tensioner (and then did not over-tension) and that got rid of the zip tie flex.

I also lowered the whole thing about as low as it will go.

I didn’t really like the available dust shoes so I made this one on Thingiverse. It just replaces the outer half of the standard 660 tool mount.

I’m very happy with the aluminum cuts I was able to make!





Seems like you could design that in two pieces that screw together and get rid of the supports…