C3D Probe 2mm Z Error

I appreciate the thought there but I surfaced the piece first so it was within a few thousandths of level. I ran the surfacing bit over the whole thing to find the low spot, dropped it a tenth of a millimeter and “flattened” the whole piece.

I then zeroed the Z (using XYZ probing) on the corner and ran the op to use the 1/8" bit to cut the text. That came out nice, just shallower than desired. I just remeasured the pocket, it’s .165" vs. the 0.2" it should have been.

I went ahead and ran the V carving operation next and that’s when the weirdest thing happened. I rezeroed Z using the z-only option and making sure that the touch probe was entirely on top of the work piece and then ran the program. The bit barely touched the work piece and by the 10% mark was completely above the work surface by a mm or two - I couldn’t exactly measure.

So I don’t know what to think at this point. I’m going to come up with a dummy file to cut three different depth pockets and see if there’s a pattern that helps point to what is going on.

@n_maher Check that your Z pulley set screws aren’t loose. Sounds like it might be slipping.

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Wouldn’t that cause inaccuracy in the middle of operations not just at the start of finish of a “layer”? I’ll check regardless but seems unlikely and thanks for the suggestion.

Most likely.

Can you try a test milling “stepped pockets”? Create a circular pocket that is 1mm deep, inside that, a smaller pocket that is 2mm deep, and so on until you get to 6mm or so. If the first layer is off, and all others are stepped 1mm down, it’s most likely a zeroing issue. If they’re all off, there are other issues. Knowing exactly how far off makes a difference.

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I was planning something similar but will layout the programming of that tomorrow and see if I can get a little time in the shop in the evening to make some wood chips.

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So something is definitely not right. The test pocket came out mostly ok, with the progressive rings each stepping down a consistent amount and close to the specified .100". Some were .093 and some were almost exactly .100" which seems like it’s probably within the accuracy of the machine.

However, then I started to run another sign program and things went wonky. Midway through cutting the first pocket the machine must have skipped a beat (slipped) and on the third or fourth pass (I was multi-tasking) I looked over and the cutter was no longer making contact with the surface of the workpiece. So weird and frustrating. I guess that means that it’s likely I have a belt tension issue. I’ve attached the code in case anyone wants to take a look at it. I’ll be trying to adjust the belt tension this afternoon and then I’ll try to re-run the program and see if that cures what ails it. Otherwise something bad is happening when I save the G code out of Carbide Create. I don’t see any other ways that a z-axis step error can occur mid-cut.

trash_op2-1.nc (122.6 KB)

It could also be the Z pulley slipping on the motor shaft (check your sets crews?) or the endmill slipping into the collet (are you are using the right collet size for that endmill, and is it tightened enough?)

EDIT: the g-code is fine

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Checked the z-axis tension, it wasn’t super tight but wasn’t exactly loose either. I’ll go check the set screw now.

And yes, it’s a 1/4" endmill in the stock 1/4" collet so that should be ok. I do tighten it pretty tight and also, when the endmill allows, try to make sure that it’s bottomed out inside the collet so it has no option for vertical movement during plunging.

Set screw was tight. After adjusting the belt tension I re-ran the sign cuts and everything seemed to work ok. I need to double check the total depth of cut but it was at least behaving better.

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I’m still getting a little inconsistency in cuts but I think I’m down to needing to fine tune the machine so I’ll spend some time with that and report back the findings at some point. Otherwise I got one project done today, a very simple sign for the MTB trail network that some of us built and maintain. It has no signs currently, I am in charge (self-appointed) of changing that.

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