Question about side finish / 'dinging' and proper material measurement [PG settings]

Hello all! I searched a bit and I am sure this has been discussed however: I noticed the side having a lot of angular slices ‘chips’ that looked like laser bounceback or sorta hourglassing (PF Thick acrylic w/ stock settings). This is with proof grade acrylic. I noticed the focus height of the material set to 6mm or what not… I measured with my calipers (two pairs) and got 5.85. I figure some of that is the covering, right? Needless to say the side imperfections went away when I matched what I measured.

Is this just a QC thing? Am I missing something or were sacrifices made for other cut variables going smoothly when they narrowed it down to 6mm focus height.

Thanks in advance! I was trying to get some photos but I’m lazy and did not setup my microscope since I loaned it to another Makerspace. I know pics say a thousand words but I think we have all seen the stripes down the side of cuts like the laser is suddenly boosting power and extra material is lost or it bounces back… I don’t mean ONE where it starts and or stops I mean many scattered around the cut length. Just wanted to make sure GF is aware / known and it is just part of my own ignorance as to why.

Also: I was wondering if as the laser strikes the material the ‘extra’ thickness if measured in for this is thrown off by neighboring vaporization of the covering before the beam advances? Just spitballing.

It’s called flashback…


Is it? Because when I adjust the proper thickness it goes away completely. Interesting…

Yep! You’re firing a laser beam that’s burning through plastic and hitting the metal grid underneath. It heats up the metal to a higher temp than the air in the chambers and you get that effect. You’ll notice the pattern corresponds to where it touches the grid.

If you want to defocus the beam a little (change the height of the focal point) that will reduce the edge effect, or you can put something underneath it. If you defocus the cut, it might not make it through in one pass though, so check it before lifting the material to make sure it doesn’t need another pass. (I prefer to cut thick acrylic in two passes anyway, you get a much more vertical profile on the kerf.). :slightly_smiling_face:


I see, thank you. I noticed my other cuts were stock settings were smoother. My adjustment just created MORE ridges but very even repeating pattern. Fun to learn to little personality quirks of new equipment.

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That’s specific to the material/thickness. Everything you cut has it’s own quirks. (I like to keep notes when I test a new material so I remember it the next time I pick it up to work with it. The list has gotten long.). :smile:


Thanks for the answer @Jules, that’s right. I’m going to close this thread - if the problem reoccurs, go ahead and post a new topic. Thanks for letting us know about this!