Knots in proofgrade, wasting material

Just received my order of 15 sheets of 1/4" Walnut plywood. I faithfully clean all my lenses and mirrors prior to each job and clen all my fans about once a week. For this particular job, I’m cutting out two large panels per sheet, each measuring 19" wide by 5 1/4" high, with interior cuts. Both panels cut perfectly except for one tiny interior spot where the plywood obviously has a knot and will not cut through, so I’ve wasted two sheets. I’ve tried getting in there with an exacto knife but it’s just too thick to cut cleanly.

One thing to note is that the default proofgrade cut settings DO NOT WORK (The default is 151, full, and .18 I believe) and will not cut through the material. I’ve had to adjust the cut settings manually in order to get it to work. My manual Walnut cut settings are 127, full power, .15 focus. This setting cuts through the material nicely every time, except for those pesky knot spots.

I don’t really think there’s a workaround for this as it’s a problem inherent to the plywood, but at $32.50 per sheet it starts to cut in to my profit margin. After doing a topic search it appears this has been a problem since around 2015 or so? Anybody have any suggestions? I feel like I keep buying Proofgrade plywood and just cross my fingers and hope there aren’t any more knots. It’s very frustrating.

Glowforge will credit the cost of PG materials that don’t cut using default settings, but that only helps you get replacement material from them.

They don’t monitor this forum, so you should use the “contact us” form on the support page.

The best option for dealing with inconsistent materials is to test and find settings that will cut thru. I do it with every sheet no matter the source before a large project. It’s a chore and shouldn’t be necessary but that’s what is needed to ensure success.


I do that as well. I use the “material test” and try out various cut settings till I find the best one for the sheet. The probelm is that there’s no way of knowing where a knot might be, so the test may work fine for finding the correct setting that works for 99 percent of the area being cut, but not for the 1 percent where the knot is located.

I’ve only had one sheet of Proofgrade that didn’t cut perfectly in 3+ years. I told Glowforge, they gave me enough store credit to cover the replacement and shipping. Part of the high cost is the warranty on the material.

That said, some of your cuts look like you’re just not getting enough power to the material… and you’re not successful with Proofgrade settings… which suggests either something is wrong with your machine or how you’re cleaning it. There’s only one mirror you can clean, what all are you hitting? Are you missing any of the 7 optical bits that need cleaning, how old are they, and have you ever tried something stronger than a Zeiss wipe? On occasion I need some 99% IPA and a q-tip to truly remove all the film on a window or lens.


The only thing that I’ve learned with proof grade is that I cannot trust it at all. When I got my last batch of proof grade, which was a replacement for some other proof grade that did not cut correctly, I took my calipers to see how thick each board was and to my surprise none of them were the 1/8 they actually claim to be. Be I have one that’s almost a full millimeter thicker than what it should be and so what I’ve done is I’ve marked one now with what my measurement was so I can adjust my patterns accordingly. I have never been able to cut proof grade at its default

There are two - the one on the left underneath the side top panel and the angled mirror in the head. The left side one is protected by a window that should be wiped clean with a Zeiss wipe.

Technically you could argue that cleaning the window is not cleaning the mirror but that’s a distinction lost on most users and could lead to people ignoring it when cleaning.


…or worse, trying to take it apart to get to the mirror. I never put anything past anyone. :smile:


Please talk to if your PG isn’t cutting through properly!

Sheets of wood without knots are much more expensive, but that’s the material we use for both outer and inner plies of Proofgrade plywood. If one sneaks through, it’s a quality defect from our lumber supplier, and we will make it right for you.

If the standard settings don’t work, that’s a separate problem - let support know as well and they can help.

Regarding thickness, we specify the tightest tolerances we can. There’s still significant variation, and we design the Proofgrade settings to accommodate the range of thicknesses you’ll find in the material.


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