Post date: Jan 10, 2014 2:58:41 AM
My Z axis has given me a bit of trouble lately. Firstly, a couple nuts came loose, meaning the stepper would turn a shaft that may or may not cause the actual axis to move, depending on the current position of the nut. This caused a few days worth of headaches while trying to etch a PCB. A little thread locker and some torque fixed the problem.
Secondly, I decided to take a slightly fancier approach to etching PCBs and actually account/compensate for variations in copper-clad thickness (and clamping imperfections). I accomplished this by probing the height of the board at various places, then wrote a python script to adjust the Z coordinate when milling the boards. (More details will hopefully follow sometime in a later post). Since the boards don't vary in height all that much, the changes were pretty small- generally a few mils at most.
My old method of using a chunk of tubing and hose clamps to couple the steppers to the leadscrews thus became an issue, at least with the Z axis. The tubing would twist quite a bit before actually turning the leadscrew- definitely not accurate (or precise) enough to do the small variations required.
This led to purchasing some new couplings, shown below. For the Z axis at least, they were a drop-in replacement, and now the axis can move up and down consistently in 0.0005" increments. Much better!
Left: A comparison of the new couplings to the old ones... guess which one works better?
Right: The new coupling installed in the Z axis