What do you check first when Z height starts wandering?

[JohtoElm]

I am trying to finish a batch of Christmas gift parts and noticed my Z height drifting just enough to mess with tolerances. Parts are still usable but the depth is not as consistent as it was earlier in the year. Nothing major changed in the setup so it caught me off guard.

When you see this kind of Z drift, what do you recalibrate first. Tool length offsets, spindle tram, backlash, or something else. I am trying to fix it efficiently without chasing every variable at once. Curious how others prioritize their checks when accuracy starts slipping.

 

[Alan]

From what we see pop up most often this time of year, people usually start with the simple mechanical checks before chasing software. Things like Z coupler set screws, thrust bearings, and even gibs changing with colder temps tend to surprise people. Do you notice the drift getting worse as the job goes on or does it reset after a power cycle?

 

[SkullFace]

I’d start with the simple mechanical stuff. Is the cutter pulling up or walking in the holder? Is the collet worn? In CNC machining, a tiny slip in the holder can ruin depth consistency even if everything else is fine.

 

[Gimm3gimlet]

hi OP, before you go chasing backlash settings, check the Zaxis motor coupler. those tiny set screws can vibrate loose just enough to let the lead screw slip a few thou during a heavy plunge but hold just fine during air cuts

it’s a 2 minute fix with an Allen wrench that solves 80% of random drift issues

 

[Tom S_]

probably check for thermal expansion first. if the shop is colder now or you're running long batches, that spindle heater up can shift your Z more than you’d think

do a quick warmup routine and rezero your tool offsets while everything is at operating temp.