Z axis on my mill cutting at different depths

[natfj55]

I have a Syil X4 Plus and Mach 3 controlling it. I had a part that was .625" tall and I needed to cut a counterbore .475" deep in 2 places. The first cut was much too deep and the second cut went all the way through the part into my vise's soft jaws. I used the Syil X4 profile in the support section, so I have not altered any of the settings.

Is this likely a motor seed/acceleration issue? My speed is maxed. Should I crank it down a bit? I am also using an older laptop until I can come up with a better computer.

[Hood]

Did the DRO correspond to the depth it went to? If you command a 1 inch move on the Z Axis does it move exactly one inch?

Hood

[natfj55]

As I recall, the Mach 3 screen was reading the correct depth. The g-code definitely has the right depth too.

I zeroed the cutter on top of the part to start with.

[Hood]

It does sound then that you could well be losing steps, if the upward rapid loses steps then Mach will think the axis is higher than it is so on the subsequent move down it will go too far.
  So yes, motor tuning may well be your problem.
Hood

[Ariel_HT5_John]

My X6 was cutting deeper with each part. I found that when the spindle was switched on and the coolant pump the Z axis would move a little. this was caused by interference spikes. I fitted ferrite ring on the 0 10v control signal from the speed control unit and the main control board. Took the 240V supply for the coolant from an external source.