Erratic Z axis movement

Hi All,
Another fun day of playing with my XXL has brought up more questions. This time it was while trying to calibrate for belt stretch. I used a dial indicator attached to my Z axis plate and happily found that X and Y were dead on, moving exactly 1mm when told to. All axes had a problem where, approximately 70-80% of the time they would take a double step, moving 2mm instead of 1, but that was easily recognizable and I just divided the number in half when taking notes. The problem came when measuring the Z axis. Even when the other axes would take a double step, it was consistently the same length. The Z axis rarely gave the same answer twice. The pulley set screw was definitely tight, no help there. I noticed one side of the belt was a little looser than the other so I adjusted and tightened it, still no bueno. Finally I just took a series of ten measurements and took the average (range of 0.032"-0.038". Should be 0.03937) and reset $102. That helped a little as the next 10 measurements were within a tighter range, but still far from consistent. Just to make sure I’m doing this correctly, I open the MDI window in CM, type /$102=45.0071449 and hit Send? Any other thoughts as to how I can fix this?

Also, would an upgrade to GRBL 1.1 and CM4 help with the double steps? I’ve heard it often helps with the stutter I get while manually jogging. Is there an instruction set that spells out every step for upgrading/reflashing GRBL with 1.1 for us simple-minded window lickers who have never coded? Thanks again, all!

Please see GRBL 1.1 and Carbide Motion 4

The CM4 upgrade is purported to address the v3 jogging “stutter”, however the loss or deprecation of other key jogging features are a non-starter for many.

With regard to your Z-movement being so far out of calibration, I’d be looking at other potential sources for error… are you running a current version v2.4 PCB? I’ve not performed this test/calibration yet, but I beleive I have seen @mikep posting up calibration spreadsheets?

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What kind of losses are there with 1.1? I’ve only just started to learn all this so it wouldn’t be hard to adapt to something new if it means more precision.

My PCB is v2.4

For doing this sort of thing, my suggestion would be to use the MDI and enter precise coordinates — no need to worry about fat fingers and incidental double-clicks.

Perfect! That was exactly what I needed! My Z is all set and I even went back and found that X and Y needed a bit of finer tuning. Thanks for the awesome help!