I made my cnc router with 80/20 linear rails--shaped plastic blocks that fit in the 80/20 rail. It seems to work fine on X and Y. I have had a bit of slop in lettering, so a small entry divot gets carved when making a cut like the crossbar on a capital A. I went through the bearings and tightened them up, greatly improving the divot. Now the Z axis sometimes loses registration, probably the stepper missing steps. It seems to be in the up direction (which makes sense), causing the bit to suddenly go deeper than planned in the work on the next plunge (or into the spoil board, >1" off). I'm using a Bosch router to power the bit. All the drive is done with 1/2" lead screws, 2tpi X and Y, 10tpi Z. Direct drive with 380 oz-in Nema 23 steppers/Gecko G540.
Things I could do (comments please!):
1. Add a spring to take up the router weight.
2. Replace the Z bearings with twin round linear bearings.
3. Replace the Z bearings with rectangular linear bearings.
For Z do I need a single rectangular linear bearing, or two in parallel? Two opposing? This is my central question.
Writing this I realize that I am assuming the problem is the bearings. It could also be my delrin nut on the lead screw, though the bearings seem more likely.
Thanks,
Steve