Source: Mantis MachineThe 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.
