# 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 you’re moving only a couple of microsteps if that — you need to calibrate for a longer distance and accept an average.

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

Lets say your calibration steps are “40”. That means, to move 1mm requires 40 steps. 1 step is .025 mm or 0.000984252" . The machine can’t (very accurately) move less that .025mm (about .00098xxxxx"). You asked to move .050" (1.27mm), or 50.8 steps. It can’t move “.8” steps. You’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. I’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.

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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.

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