Two pieces cut from the same file don't match

Has anyone experienced this issue? Occasionally, I will cut two layers of 1/4 or 1/8 material and adhere them together to make it more rigid.

Last year, I did a sign that was over 4 ft long using the pass through. So I cut two sheets of the plywood with the intention of gluing them together. It was a rectangular shape with rounded edges and words cut out of the middle. I cut the design 4 times and none of them matched, each was slightly different than the other. Even the rectangle shape itself wasn’t square even though the SVG file was clearly square. There were many steps using the pass through so I just attributed it to the fact that the alignment was off just slightly each time and that was probably the reason why.

Then I noticed some something similar recently where I was making a much smaller sign, about 10 inches square. One layer was 1/4 inch plywood and the top layer was 1/8 inch acrylic and the edges were off. I was engraving on the wood backing and doing 3D lettering on the acrylic side. And I realized that when I flipped the wood over, it aligned perfectly to the acrylic. So I decided to cut the wood shape first then flip it over and engrave the other side. When I cut the wood and flipped it over, it wouldn’t fit in the space that it came out of. While flipping and engraving fixed the “problem” I’m confused why the GF can’t seem to cut a perfect square.

I’m guessing it’s either a belt tension issue or somehow the laser head isn’t in perfect sync with the drive belt. In both these instances, I was cutting square/rectangular shapes with rounded corners.

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The kerf is different for 1/8" acrylic and 1/4" wood. Therefore you will get different results from the same file if you don’t adjust. As for flipping parts, the Glowforge cut is not perpendicular, it is slightly angled so there is a very, very slight difference between the front and back of a piece.

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Thanks for your reply. It definitely wasn’t a kerf problem. That small of a variation would have been fine.

Are you saying that the Glowforge cannot cut a square or rectangle with exact 90 degree angles?

I am not saying that the Glowforge cannot cut a square. I am saying that the cut edge is not straight/perpendicular to the plane given the nature of laser beams.

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Oh, I see what you’re saying. I misread your reply. That’s not the issue, looks like my laser arm might need adjusting.

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Thanks Dan. I will give this a try.

Any chance there is a video tutorial to show exactly how this is done?