Step 5: Installing the Rack Gears (Y Axis)
Again, we use the epoxy to attach the gears onto the MDF. In addition to heavily applying epoxy to the board itself, make sure some is spread on the side of the drawer bearing, that way there is stability in two dimensions. Do your best to prevent epoxy from getting in places it shouldn't be -- you may gum up your motor.
It works out that the rack gears extend a little bit off of each end. This is a good thing -- it enables the gear to travel the full length of the board without running off. The stepper motor will be offset just enough that if the gears only covered the board's length the whole motor assembly would get stuck at one end.
Also install the circular gears onto your motor at this time. Mine had a set-screw, but you may wish to use some JB weld to hold your gear in place. If you go that route, the joint needs to fully cure before you try to use it, or you risk the gear popping off!