Getting started cutting non-proofgrade hardwood

Oh hey - someone just linked to this post: Depth Adjustments which gives you a nice pattern to use to test on wood. It’s a bear to set-up the first time (you have to program each level to the speed indicated) but then you leave that on your dashboard and each time you get a new piece of wood run it on an edge

This doesn’t take into account multiple passes, so maybe not for your 1/2" stuff, but in general having a pattern something like this is great if you intend to use non-proofgrade


I modified the design originally to be a “standard candle” so even the 1/2" will show what happens at those settings. there is no reason you cannot run the same designs at a second pass and make a note of the difference in ink on the piece. I keep a collection of these to refer to when deciding what particular effect I want.

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Good news, I was able to test out the 145/full/2 passes on some 1/2" birch hardwood I had and it worked pretty well. However, in some spots it juuuuuust didn’t quite cut all the way through and my attempt to finish the job with an exact knife later failed. So I probably need 3 passes…

But here’s my question, if the 3rd pass is barely needed, that means probably 90% of the laser’s efforts will be wasted not cutting wood. That’s fine with me, but does that damage the crumb tray or machine in any way? I’d rather not setup a complex job as this is all so quick that another pass is fine, I just want to make sure I’m not damaging anything.


You’re likely to get serious flashback at that point. I’d set up a job with 3 passes at full power and then make several cuts at different speeds until you just barely get through it. Speed 145/150/155/160/… up to like 180 or so. see if they get through it. If they all do, run it again, this time 180-200 or so…

You’ll get the exact speed you need to reliably make it through.

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Very interesting.

  1. I probably can guess by the name, but what exactly is flashback?
  2. In your example here, I guess I would work in reverse right, maybe testing 3 passes at 180 and if that doesn’t make it through, then try 3 passes at 160, then 3 passes at 155, all in different spots on the board to see what barely makes it through. Then I know what is the sweet spot to run the job? Or are you thinking I run it 2 passes at 145 (like I tried already) to almost make it through and then do one lass single pass at 180-200 to do the last little chunk? I’m imagining I don’t want to start my testing at 3 passes at 145 as that was my original thought which we think might create the flashback :slight_smile:

The main thing is without snapmarks, I can’t reliably inspect the piece between jobs and put it back in the same spot.


You can do it all in one job. It’s easy to set up.

Let me see if I can find my post on it…

There you go. Easy test process.

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Perfect, I will definitely try that. Reminds me of the temperature tower I have used in 3D printing :slight_smile:

As for flashback, I guess it can leave some nicks in the back of your material, but is it actually harmful to either the crumb tray, machine, or eyes or anything?


Crumb tray is pretyt burly, you’re fine.

Machine is built for this, so it’s fine too. (don’t try to cut laser-reflective materials, like copper etc. Google “co2 laser reflective materials” for more information)

Eyes should be fine unless you’re intentionally subverting safety protocols. Use safety glasses if you’re operating in class 4 modes if you want to be more safe.

Anything? Well, your materials are in serious danger of getting a solid lasering. If you tie a mosquito to a tiny Dr. No -esque supervillian interrogation table, she’s in trouble.

“No, Ms. Mosquito, I expect you to die!”

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Not generally. The exception is a material like corrugated cardboard where it can lead to a flare up from the bottom of the material that can then shoot down the air channels in the cardboard before erupting into flame.

For everything else it’s mostly an aesthetic issue

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I hate to ask, but what is “operating in class 4 modes”? I have a GF Basic and never intend on opening the door while running or anything…

If the Pro operates without the pass thru shields it is in Class4.

What @rpegg said. Basically it means “there’s a chance this laser might escape the machine, wear glasses.” If you don’t trick your GF into operating with the door open on a basic, you should be fine.


So this is very interesting…I bought some 1/2" red oak and did the speed test graphic mentioned in other posts and after doing this and some other separate tests, here’s what I learned:

  • 100/full in 1 pass went all the way through and gave some flashback
  • 125/full in 1 pass went in only maybe .25in. I tried multiple passes and after 7 passes it still wouldn’t go through. So I instead started over and did one pass at 125/full at the full 0.5in focus height, then one at 0.25in. But that pass left about 0.1in left, so I started over and did the 125/full at 0.5in, then 0.25, then at 0.1in (all without moving the part) and it still didn’t go through. So I gave up and just did the 100/full in 1 pass even though I was a bit concerned about fire.

So here’s my questions…

  1. Why did 100/full go through (and then some) and yet 125 had major struggles? Are these speeds significantly non-linear in their effective strength or something? I would expect 125 wouldn’t be that dramatically different than 100.

  2. Also, do you think I did this right on the multiple prints at different focus lengths? I thought that would have worked.


Yes. 50 is not half of 100. 200 is not twice 100.

GF uses its own speed and power setting scale. Part of the reason is so that settings for Basics and Pros can be used interchangeably until you get to Full power - for the Basic that’s 40W and for the Pro it’s 45W.

They did release a spreadsheet back when they switched from their initial scalable settings (and inch per minute speeds) to their current scheme. If you search you should be able to find it and get a better sense of how the numbers scale in relation to each other.


Speed of 100 is 4 inches per minute. Speed of 125 is about 13 inches per minute.


Wow my suspicion is right. That seems odd but thank you for the info. I guess I would need to do some tests with small increments between 100 and 125 to really get this right.

Thanks much to you both.

You can do it in one test.

Testing is fast and easy, use this method and you’ll be able to test any material in minutes.

Yes, definitely. In fact I used that to determine the 100 vs 125 vs 150 etc. Now I just need to modify it a bit to run 100, 105, 110, 115, 120, 125 now that I know that the speed numbers are non-linear.


When you are running at full blast with no flame happening the Glowforge will cut much deeper than if there are problems. At first I thought it was variations in the wood but those cuts near the magnets did not go through, When re-cut those parts that were not cutting all the way through, still did not cut through. As best I can tell either or both of two things could be happening : #1 the char itself is more resistant to the laser than bare wood or #2 the wood is hardened by the heat and it takes more to cut it. Whatever is the case there is rather a difference with the second pass that it does not cut as deep as the first, even as the same settings.

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