Inspecting thin plywood for voids and glue

I just posted this info as a response to a problem, and realized it could be helpful to others if I posted it on it’s own here.

Sometimes plywood has hidden voids that are filled with glue. The laser often won’t cut all the way though the glue spots. Sometimes you can get through with another pass or two of the laser, or just finish the cut by hand with a hobby knife, but I find it best to just avoid the voids if possible by identifying where they are.

I use this worklight from costco; with the kickstand folded it lays flat on it’s back.

bb ply over the light, then turn it on. (it’s really bright)

good over here.

Big ugly glue-filled void.

Avoid this area for cuts, or allow for multiple passes with the laser. There may be significant charring of all cut edges if you run enough passes to get through the glue. I find that it often takes me 4 or more extra passes for stubborn spots, which can take a lot of time with a complex design.

Pro Tip: Turn off the lamp before removing the ply so you don’t blind yourself. It’s still really bright.



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I remembered someone talking about the method, but I didn’t see it just now in a tag-search… hidden away in Beyond the Manual!

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Yeah I like to add the link to duplicate/similar posts to help with the interconnectedness of the forum. Now both posts have links to each other in the summary section. Off topic but I wonder if there is a way to do that without adding an otherwise useless comment?

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Matrixed! :grinning:


Are you still seeing spots in front of your eyes…lmao… Thx for the tip. :smirk:


no, I learned my lesson after the first couple of dozen times…


Could you say which model, please ?
A quick search throws up several, but not sure which one it is.
Many thanks,
John :upside_down_face:

the CAT (Caterpillar) branded lamp that I have is marked ITM./ART. 962841 and has a manufacturing date of 06/2016.
The way that costco orders and stocks stuff means that this particular lamp may or may not be available, but any sufficiently bright lamp or flashlight will do the trick.


Thanks for the heads up on that one.
John :upside_down_face:

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You can also do it with a plain table lamp in a dark room. Take off the shade, and just hold it up.

I mask first, then mark it with a pen over a lamp.

“There are more ways to kill a cat than drowning it in cream.”
Not my favourite quote, but it fits the bill (to use another !)

John :upside_down_face:

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Eeeeeewwww! Lose that one! :face_with_raised_eyebrow:


Sorry. :blush: