Partial stair stepping

So I’m not sure what’s going on here. It’s like the first 3 passes are getting off in the Y direction, but only on part of the file. You can see the stair stepping on the bottom edge only. Everything else cut perfectly. Any ideas? I’ve restarted the machine, re-homed it, checked wheels/belts/etc, and my stepper power is already tuned up.

I would like to note that I cut birch ply before and after this piece and the machine cut the wood just fine.

This is a polycarbonate plastic. Cutting using a spiral o flute upcut 1/4. 0.03125" depth per pass, 30IPM.

It could be belt tension or loose GT2 pulleys, check to see if when the machine is on you can move the carriage with your hand back and forth. I had this problem and its quite tricky to spot.

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That is a bit odd, if it missed a step I would expect the top edge to show a problem also. Are the vertical dimensions for the cutouts what you expect them to be?

@CristianHinz I’ll give a look over on the pulleys. But like Allen said, if it were getting off, it’d be off on both the top and bottom edges.

@AllenMassey my vertical dimension were correct. It cut the exact depth I called for along with the tabs. It has to be communication to the machine because the drawing is correct, when I program in aspire the tool paths are correct, and when I visualize in UGCS, all the lines are dead on top of each other.

Well, if you miss a step it would show up top and bottom, but if the belt is stretching or the pulley slipping on the flat you would get incremental offsets.

If the bit plunges on that line it is probably the result of flexing on the X axis. You could try ramping your plunge.

@Earwigger I’ll definitely give that a try. Thanks.

and check your v-wheels front and back on your gantry and Z.

I’ve always found acrylic very difficult to cut when compared to HDPE or wood. But all the suggestions so far are good ones to rule out.


Thanks for all the suggestions. I slowed my IPM down and added ramps to the cut paths and that seemed to work great!