Repeatibility Fail

Probe XYZ then note the absolute XYZ coordinates, then repeat multiple times… I’m seeing variability in the absolute XYZ coordinates each time I probe as much as .5mm. So I can’t shut down, power on, probe and continue on a project without the probe variability causing a shift/offset in my cut part.

I probe with a piece of drill rod, and hold the probe against the edges during the probing sequence, yet still the variability.

It would be helpful if others verify the repeatability on their probes routines, thank you.

Are there any variables in the probe routine that could improve repeatability?

For now, looks like I’ll be abandoning the probe and resorting to conventional manual methods.

I use the probe everyday with no repeatability issues

Probe XYZ then note the absolute XYZ coordinates, then repeat multiple times… compare coordinates. You’ve done that, or is it that your processes don’t demand probe repeatability?

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Are you using a router or a spindle. More than likely your readings are deviating because of the bearings in the router, and 0.5 mm is really not that bad, its a desktop CNC not a HAAS.

0.5mm runout on a router or a spindle? Think about that…

On a trim router yes it is possible, things wear out over time “think about that…”

  1. If a router had 0.5 mm of run-out it couldn’t spin a tool 18000 rpm without the tool snapping off… the dynamic load would be extreme… I wouldn’t want to be close by.

  2. When probing, the tool is not rotating therefore run-out is irrelevant to the subject of repeatability in the context of this subject.

  3. Probe XYZ then note the absolute XYZ coordinates, repeat multiple times (without rotating the tool if run-out is a concern of yours), compare coordinates (should be same else not a repeatable process/system/design/configuration)… that would be helpful. ty

I ran some tests… the variability is rooted in the machine homing, not the probe. Machine zero is not an absolute/repeatable location so if you home the machine (after power up) and then probe the absolute values relative to home will vary.

Running the probing routine multiple times within the same home position (not powered down or re-homed) is repeating within 0.03 mm over a five test sample and that is very acceptable.

Variability in the machine absolute home position is also acceptable, as only the work home position need be repeatable and its offset values from home are irrelevant.

The probe is repeatable, stall homing is not and that doesn’t matter.

Concern resolved. Done.

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My understanding is that the work home position is relative to the machine home. and if stall homing (machin home) is not repeatable, then the work home position will not be repeatable. Please correct me if I am wrong.

The Work Home (G54) has very little to do with Machine Home. Work Home is where you set your xyz coordinates on your workpiece. Whereas Machine Home sets the limits (max. machine travel distances) of the machine itself. If you set your work coordinates & zero each axis then those positions should be repeatable throughout the carve.

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On the xcarve, setting machine home places the spindle or router at the front left of the work area (0,0). Which will prevent the machine from going out of the work area. If I set the work home coordinates, they are relative to the front left of the work area or (0,0). When I turn the machine off and back on, if I move the router/spindle to the machine home using the limit switches ( bump stop on the Onefinity) , it can then find the work home coordinates. Allows me to do a rough cut on a work piece. Turn the machine off. and the next day I can do the fine cut on the work piece. I thought the Onefinity works this way as well?

I find that regardless of where you park the machine you still need to machine home on power-up, and of course after homing you need to re-probe to re-pickup your work home position.

I tried parking at my work home position, power-down, power-up, set work home position to parked position, then carrying on… but the machine reports itself as “unhomed” and on toolpath execution it is not behaving as though the work home position is set proper.

I would expect that any machine without absolute encoders will require homing at start-up, so I don’t consider the 1F process to be unusual.

Stall homing is not going to be as exact as a dedicated home flag. I believe that with the breakout board you can add switches. I would add a manual switch so you can turn them off after homing so they don’t act like the hard stop while in normal use. I would use something like an opto or hall effect type switch.

No when you turn your machine off and then on again you don’t want you home you machine again. You just want to rezero your Z .X and y should still be at zero .as soon as you home your machine you have lost your work zero.

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