Thank you so much!
Actually I do have a question about cutting something that thick…Do you have to make any changes to the focus height that is defaulted to 0.125 in? I had this argument/discussion with another laser manufacturer once and the premise was that as it cuts deeper and deeper, you are “out of focus” because the remaining material the laser is now hitting is much lower than when you started. Again, I will definitely just try and if it works it works, but I am curious about this conceptually 
Thanks!
Well, if you’re cutting .5 materials you should have it set to .5, not .125 (1/8) - when you put in non-proofgrade stuff the focus height is blank, and it’s the first thing you should set (because it helps the camera adjust)
As for resetting focus height, I haven’t done it yet, but I haven’t tried cutting thicker than 1/4 - there is a lot of talk about it, and the answer seems to be: if you’re doing multiple passes, you might as well.
So here’s the thing - there are 2 places to set the focus height - the first one is the top right “use uncertified materials” box - that should always be the full height of your material. The 2nd is in the cut settings box, bottom left there is a “focus height” box. That defaults to the “uncertified materials” setting, but you can override. So for the 1st test, I’d leave it as is, but if that doesn’t work and you’re moving into further testing, I would definitely consider switching that to .25 for a later pass
Isn’t that clear as mud 
2 Likes
Aha, makes sense. Sort of
The reason I had 0.125 is I was looking at an existing job that was using PG 1/8" and I hadn’t realized about the uncertified materials box, now I see that.
I will definitely try just as is, but it’s interesting because I don’t entirely understand the focus setting box as I would think that on a 2nd pass the focus would be “further away” and thus a larger number because there is physically now more space in the air between the mid-way cut part of the board and the laser. But then by that token my idea fails since there probably isn’t 0.5" of “focus distance” between the laser and the top of the board at the outset of the job simply because the board is 0.5". So I think I need to get a bit smarter on what focus distance even means
Very helpful, thank you!
I have tried cutting thicker plywood and someone suggested for the first pass set it at actual height, then on the next pass set the focus height about half way or the thickness of what is left to cut. I tried this and found not only did it cut nicely it also had less over burn on the surface. There really are many factors to settings, like if the wood has a lot of resin or if it is a hard wood or a soft wood so test runs are still important.
5 Likes
Focus height is the difference between the top of the crumb tray and the tip of the laser - so .5 is max, because that’s physically the amount of space available
If you search the forums you’ll see a number of posts on how to cut without the crumb tray - and if you’re cutting something ~1.38" tall then your focus height will be 0 because that’s approximately where the top of the crumb tray is. If what you’re cutting is 2" you have to do the math to figure out 2 minus 1.38 = focus height
*each crumb tray has some variation in height - so measure yours to do this correctly
Check out: Problem for setting material thickness (without tray) for a visual aid
Very cool. Just to be sure then, it sounds like I can still cut 0.5" thickness wood without removing the crumb tray correct? I may do tests both way as both you and @nancielaing suggested in the prior post(s) on the 2nd pass and see what happens.
Thanks!
Absolutely
.5" fits with the crumb tray
~2" fits without the crumb tray but you’ll only be able to cut (reasonably) the top .5" of that
1 Like
One thing to check when you hit the 4.7" to 5" is the clearance you have with the air assist cover. It hangs down low and I always move it over my tall material to make sure it doesn’t rub somewhere. (With the machine off just move the head over the material and eyeball it to make sure.) Better safe than sorry.
3 Likes
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
2 Likes
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.
1 Like
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.
Thanks!
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.
1 Like
Very interesting.
- I probably can guess by the name, but what exactly is flashback?
- 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
The main thing is without snapmarks, I can’t reliably inspect the piece between jobs and put it back in the same spot.
Thanks!
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.
1 Like
Perfect, I will definitely try that. Reminds me of the temperature tower I have used in 3D printing
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?
Thanks.
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!”
1 Like
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
1 Like
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.