Mantis 9.1 CNC Mill

The Mantis 9.1 design is a radical departure from version 8 and earlier. Most notably, the part count has been almost halved! The current design has 13 parts, all of which can be made with a handsaw and a drill press. Also, I've traded away my alignment free exactly-constrained design for extra stiffness. Several unsuccessful attempts to eradicate the last of the slop in the Z axis on version 8 lead me back to the world of over-constrained parallel rods. My previous attempts at an over-constrained design (versions 1-5) all failed because I was unable to make the rods sufficiently parallel to avoid jamming. What to do?

The solution to this problem came to me one day in the shower— stack the two wooden endplates, and then drill the rod holes through both pieces at the same time. By doing this, we can ensure that the rod holes are exactly the same distance apart, and thus the rods are perfectly parallel. In the aircraft industry, this process is called match drilling.

Once we have a precise set of holes, it's easy to slip two sliding brass bushings on each of the rods and press the rods into the endplates. We then take the plate that we want to slide back and forth, and lay it on top of the four brass bushings. The rods hold the four bushings in alignment, and a bit of epoxy permanently attaches them to the underside of the plate. Its kind of cool that a few simple manual operations and some epoxy can trump the accuracy of a ten-thousand dollar CNC machine.

Construction Summary

The machine is constructed from 1/2" MDO Plywood, using Acme lead screws and Delrin AF nuts for motion. The axes are constrained by bronze bushings sliding on precision steel rods. Nema-17 stepper motors power the CNC mill.