Need help with very mysterious behavior

I just can’t come up with any explanation for what might be happening here and could use some help troubleshooting this. The image included shows a vinyl sticker cutout I did on my mpcnc primo that for the most part came out great. The main mystery here is the holes cutout in the lower left object (zia symbol) are quite a bit off center. Everything else, except for the second mystery came out really pretty much spot on. If you look at the gcode in estlcam (where it was generated from an svg) and in other gcode simulator, the holes are spot on in the center of the symbol, yet as you can see, they were cut out quite a bit off center. The holes are the first two things that the gcode does which should be a clue here, but doesn’t help me come up with a good explanation. I am using the v1engineering cutter and lead in on all cuts as you can see in the gcode simulator. If there was a problem cutting ‘holes’, then the holes in the letter ‘P’ would have been off too I would think, but they are spot on. The only other cut that is slightly off is indicated by the red arrow on the right hand side. One of the chiles that was cut somehow didn’t line up. Have no clue on that one either.

At first I thought maybe somehow after cutting the two holes in the zia, there was some belt slippage or somehow the cnc got ‘off centered’ but I don’t think that is the case just by looking at where everything else lines up with where it should be (looking at the simulated gcode).
Does anyone have any theories as to what might have happened? I am cutting at a .3mm depth on a piece of glass and the cuts all seem to be good.
I will try and include the gcode as you will likely need to look at it when run through a simulator.
Thanks very much for you ideas!
Kind regards,
chileEditedText3.gcode (58.0 KB)

i just noticed one other oddity that might be a clue and that if you look at the two 'P’s , and only the second ‘E’, they appear to be cutout in the wrong place (up about a mm or two). I’ll have to see of all of those letters get printed one after another, and then maybe after the last was cut, the cnc got off center.

Have you checked the ever popular grub screws?

Thanks for the idea Paul. I will check those. It does look like something slipped or got off center while cutting the second chile. The gcode does indeed cut the two holes in the zia (which are off), then the two Ps that are off and then the E that is off and then goes to cut the chiles where that second error I mentioned (the right hand side red arrow is drawn). So right there is where we might have slipped. If that is the case, it’s how the holes and P’s and E that are off but I guess everything else is off. Well really, things just got ‘out of sync’ (lost the common reference of 0 that we started off at).

You want them to not only be tight but to bear on the flats machined into the motor shafts. A little Loctite isn’t a bad idea either.

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just wanted to follow up. I went back and redid all the grub screws. They all seemed tight and I had used loctite when I initially did it. It is possible that they were not all on the flats, but I think they likely were. In any event, after redoing it and doing the cuts again, I did get a successful set of cuts. Hopefully that is indicative that the problem is fixed, but will keep an eye on things as I do more with the machine. Thanks again for the help Paul.


Glad to hear it! No matter what the cause, a success is a success.

And I’ve always thought that Zia symbol a nice piece of graphic design.