Increasing errors over a few jobs

Hi Folks,
I’ve got an XXL and I’m working on a series of pieces with very dense diamond drag engraved lines (0.004 - 0.003 line separation). I understand the Shapeoko tolerance is around 0.005", but this isn’t an issue with absolute performance.

My first piece looked the best, with a few errors where the machine put the next line too far, but I’ve noticed that the errors seem to be getting worse with subsequent jobs. These are long jobs - 6-10 hours each, so it would make sense to me if there’s some kind of wear or loosening happening somewhere.

Here are some photos:

First job:


It still had some errors, not but many:

Then I did my second job, and there were more lines, plus in many of the shapes, the engravings look different (darker or lighter) on one half of the shape.

Magnification doesn’t reveal much. The pen tip here marks where it goes from light to dark, and there is a line there, but either side looks like of similar under the microscope lighting:

And the third job is worst yet, where almost every shape in it has half light and half dark lines:

It’s not the bit that’s wearing. Here’s a picture of the diamond tip before and after - it’s pretty much unchanged:

Would appreciate any insight on what’s going on and what I can do to fix it.

If you haven’t already done it, it’s definitely worth going through and checking all the pulley set-screws, belt tensions, checking the V wheels are still tight etc. those can all shift a little on first use.

There’s some guidelines in the e-book.

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There could be a couple of things that are needing attention.

  1. Set Screws tight and one on the flat of the motor shaft.
  2. The belt tightness.
  3. Calibration of the steeper motors.

Make you self a project with a 3 inch square and make about 5 or 6 of them on a mdf or other piece of scrap. Cut the squares out and measure the squares precisely. If all of the squares are the same and are consistent but not 3 inches you may need to calibrate the steeper motors. If the squares are inconsistent then it could be your set screws and/or belt tightness.

Once you get the squares cutting consistently the same size I think your inconsistent lines will disappear. You may need to cut your squares several times to get them the right size and consistently all squares the same size.


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