Strange cut profiles - angled sides - what would case this

Hi There.

Hoping get some guidance on getting our omtech 40W laser cutter up and running properly. Out of the box it seems to be cutting a bit off. There are a couple of issues, but the one I will focus on here is that on is that the sides of thicker parts do not appear to be 90 degrees (the sides are angled). Then on the front and the back there is a very unusual non-linear profile.

I have followed the alignment guides and mirrros 1,2,3 alighment seems OK. I have also shimmed the lens head fixture to be more parallel to the base ( it was off by ~3mm in one direction). But the cut profile does not seem to improve with these changes.

Do you have any other ideas or guidance of changes I can make to get nice 90, square cut edges?

Happy to make changes, run some more test cuts to help diagnose the issue, post more pictures. Thanks!

How thick is that foam? One thing to keep in mind is that the laser beam has an hour glass shape as is goes through the focal point.

So for straighter cut profiles you would want a longer focus point lens. Most of these 40W machines come with a 2" focal length lens but you could go with a longer focal length. The spot size does go up with longer focal length so they are not as good for engraving.

Also if the beam isn’t perpendicular to the work surface you can get some wonky angle cuts.


Thank you Nedman! The thickness of the foam is 1". I put a flat piece of wood diagonal to the surface for Z distance of a couple inches and the beam burned pretty uniformly on the wood on the x over the 2 inch Z, but I see looking at your images that does not necessarly mean much when moving in the x/y at the same time. I’ll get some different focal lengths and experiment.

Another thought is that I might be seeing some laser reflectance burnign happening too. Is it bad practice to put the material direclty on the metal surface. Mine does not have cutouts or honeycomb, just solid metal.


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1" is pretty thick for a typical stock 40W lens, so I’m not really surprised about the cut profile. If you set the focus point half way into the foam that will give you the most consistent profile.

Putting the material on a solid surface isn’t bad per se, but you will have to deal with the back burns. Usually people use stand offs to raise the work piece off the bed surface when using a solid bed.


Thank you for the very helpful responses. Will do. To step back a bit, I’m wondering if there are any standardized way /test files / materials that can be used to test that the laser optics are properly aligned and cutting the way that it should be? I get the feeling that something is out of wack, beyond the weird cut angles, and I’m not sure how to diagnose/fix it. Thanks again for the amazing help!

There are definitely some resources on alignment that you can find from the “K40 Intro” at the top.

One common mistake when all the mirrors are aligned correctly to align the beam, is to have the lens upside down.