In assembling and running the MPCNC, I had to strengthen two parts and create another for wire management. I inherited this build from a friend who had a student put it together. Needless to say there were many errors, and not a few broken parts. But, this pointed out some weak spots in the design.
The clamps for the gantry on the original MPCNC use friction to hold the stepper assembly and bearing to the upright rails. This slips, especially if the holders have been overtightened or cracked, which is easy to do with PLA. In fact, this was so bad that the vibration of an early mill allowed the gantry to slip completely out of the holders and punch a hole through the workpiece and bed with the router still running. This design uses an 8/32 screw to hold the clamps to the rail vertically. This screw can either be of the self-tapping variety, or you can do as I did and just tap a hole in the side of the rail. The bonus on this is that it appeared to reduce vibration of the stepper rod with no real increase in mass. I created two versions of this part: a 23.5mm version and a 25.4 version.
The roller plates on each of the 4 horizontal steppers broke very easily when tightening the bearings, especially with PLA. I increased the thickness and printed in ABS to solve the problem.
- I was very uncomfortable with the wire management going into the Z-axis stepper. Repeated movement tends to bend the wires at the stepper body, assisted by gravity, of course. I designed and printed a wire channel holder to eliminate this problem and this will be part of a better wire management scheme with a drag chain in the not too distant future also.
Designs done in Fusion 360 from imported MPCNC STL files.
Even using ABS I did not have any fit or tolerance issues. I believe this will be printer dependent, but I do think that either PLA or ABS will work for any of these.