# Cannot Calibrate Z Axis

Guys, I have a dial indicator that has .0005" increments. I have repeatedly moved my z axis down 0.05" and get only 0.0485-0.0487ish every single time EVEN AFTER I do the math and change \$102. I even looked in the logs to make sure that the value is being input and I can see the entry. What could be going on?

The problem is youâ€™re moving only a couple of microsteps if that â€” you need to calibrate for a longer distance and accept an average.

If you need a high precision for a specific distance / dimension youâ€™ll probably need to work up to it â€” cut a sample, measure it, then determine how much more / less youâ€™ll need to take off.

Lets say your calibration steps are â€ś40â€ť. That means, to move 1mm requires 40 steps. 1 step is .025 mm or 0.000984252" . The machine canâ€™t (very accurately) move less that .025mm (about .00098xxxxx"). You asked to move .050" (1.27mm), or 50.8 steps. It canâ€™t move â€ś.8â€ť steps. Youâ€™ll get 50 or 51. 50 steps = 1.25mm, 51 steps = 1.275mm (0.0492126" or 0.05019685" with \$102 set to 40 - you can work this out with your value)

The steps per mm you are setting up will be much more accurate over a further distance. Move it .750", and it should be within ~.001 or so (maybe less). The math used is used over the length of the move. Iâ€™m not sure how the remainders are kept, but I suspect given the limited number of digits after the decimal that lots of little moves will be less accurate than one big move.

4 Likes

Well, it helps if you get the formula right! I got everything finally set up last night and got my Shapeoko Logo done. I installed the T-Tracks and will surface the T-Track Wasteboard this morning. Working on the G Code for that now.

2 Likes

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.