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Troubleshooting probe accuracy and QGL "Samples Exceed Tolerance" issues on a V2.4


Staff member
Voron Owner
Printer Model
Voron 2.4
Run a `PROBE_ACCURACY` in each corner at the qgl probe points. We are aiming for a standard deviation (SD) of under 0.003. If the SDs are all bad than a probe/toolhead issue is more likely. If one or two corners are worse than others an isolated Z motion issue is more likely.

Z issues:
-Check main belt tension: 140Hz on a 150mm length of belt.

-Check belt loop tension. Should be very taught with only a tiny amount of deflection when pressed or pulled at center of span.

-Ensure nothing is rubbing during Z motion. Specifically belt tails or gantry parts rubbing on panels.

-Check that large M5-40 bolts in Z blocks are tight.

-Test how probing speed effects accuracy. Found in the [probe] section.

-Check Z belt tensioners for excessive play or belt routing issues.

-Check Z drive grub screws.

-Check alignment of belt loops and main belts on the pulleys.

-Check all screws on gantry: Linear rails, XY joints, Idlers, AB drives.

Inductive Probe Issues:
-Ensure probe is secured firmly to toolhead.

-Ensure carriage is securely attached to linear rail carriage block.

-Ensure probe is triggered before nozzle touches bed.

-Inductive probes rarely experience a loss of accuracy as a failure mode but it is possible.

Klicky Specific Probe Issues:
-Ensure magnets are making good contact with no rocking.

-Try replacing probe and/or switch.
This GitHub project, KiloQubit/probe_accuracy, was REALLY helpful for getting my "Samples Exceed Tolerance" issues resolved. It showed more variation in certain corners and I slightly tightened those Z belts. I was using KlickyNG and also had to fiddle with the probe's switch pins a bit to get the magnets really flat. It has been very reliable since.
Found that mine was klicky was rocking on the magnets and causing the problem. When I rebuilt the probe head it was much better.