MPCNC Primo J - Z Motor Thrust Bearing

This is a modification of Ryan's excellent MPCNC Primo J cnc machine design, which can be found here: https://www.thingiverse.com/thing:4493589

The stock design uses the z stepper motor axle to support the weight of the z gantry. This works out fine for lighter routers and slower z moves. However after heavily modifying my Primo's electronics, the z became capable of 5000mm/min @ 500mm/s^2. IMHO, with a heavy watercooled spindle it became too much load to rely on the stepper bearings alone. So I drew this modified z motor mount in f360, which adds a second thrust bearing on top of the z coupler. The second bearing "sandwiches" the coupler, and takes the load off of the stepper motor shaft. To use it, you'll need a Primo J, a spare 608 bearing, and a 6mm ID washer.

Printing:

Print as is, no rotation or supports are required. I printed mine in PETG-CF, with 0.25mm layers, 45% bicubic infill, and 2mm walls/tops/bottoms. PLA and other settings should work as well.

Assembly:

First, press a 608 bearing into the mount, and mount the z motor to it. Install the 6mm ID washer over the shaft, then the spring coupler. Press firmly up against the 608 bearing while tightening the coupler set screw to the motor shaft. Now install the lead screw on the coupler. Do so such that the screw touches the motor shaft, and pull a little bit of tension on the spring as you tighten the set screw (the tension ensures they remain touching). Hint: tension is visible by glancing at the size of the slots on side of the spring... the middle of the spring should have larger gaps than the top/bottom due to being stretched out a bit. To give an idea how much tension, this slight difference in slot width can be seen in the coupler shown in the photo. If the slots are all uniformly sized, you likely need more tension. Next fit the lower z thrust bearing mount (with bearing installed) on the z tubes. Then slide the lead screw through the lower bearing, and fit the z mount onto the tubes. Tighten the z motor mount once it is in position (move the lower thrust bearing down if it gets in the way for now). Now slide the lower thrust bearing upward so it seats firmly against the bottom of the coupler. Tighten the bottom thrust bearing mount.

After assembly the screw should have no vertical play in either direction, and the should still rotate freely. If you haven't installed your spindle mount on the z tubes already, do so now. Then slide the assembly down into the core, and turn the leadscrew to finish dropping it in. Finally, resquare/tighten the machine as needed, and enjoy milling!

Category: Machine Tools