Wood is (mostly) a hydrocarbon, which burns readily. There are lots of glue formulations, but a typical one for indoor-rated plywood is urea-formaldehyde, which has a significant amount of nitrogen in it. This needs to vaporize through combustion, which means you need to be at temperatures that allow the formation of nitrogen oxides, a.k.a. smog-forming compounds. Regardless of the specific glue chemistry, there’s a minimum temperature required to achieve combustion, and if you don’t get there, you don’t get a cut. Simply slowing down the laser movement allows the beam to dwell on a spot longer, heating it to higher temperatures.
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Just as an update, had a change to do a test with my 3.5mm ply. Was able to cut through with 18 passes at 0.2mm depth per pass (3.6mm total), at 1mm/s (60mm/min).
It’s slow, and requires a lot of passes. But I got through, and the edges are actually quite clean.
I tried 3 passes at 0.2mm/s @ 1mm depth, and it didn’t get through the first glue layer. The glue only seems to burn when it’s right at the beam waist, and the fine layers help with that.
I have not tried to optimize this a ton, but I was not able to get through at 0.4mm per pass at 1mm/s
I have some 3mm plywood that I was having inconsistent results with. I finally went to using 40 passes @ 0.1 mm step to cut through it successfully.
I have been using poplar wood which is very light and can be cut very fast and nicely. I was able to cut trough 3mm thick plates with 3-4 passes at 200mm/min. With 4 passes the parts fell right out while i had to poke them a little bit when using only 3 passes.
Also i noticed that less passes at a slower rate (<50mm/min) cut much worse. The edges are burnt badly and it doesnt go as deep (at least for this sort of material).
I cannot cut 2 mm birch plywood (the one used for aeromodelling).
After many pases it just scratches the surface of the wood
I tried something in the middle of what it is indicated in this thread and in the Snapmaker’s ‘Definitive Guide’.
I used:
Jog Speed 1500 mm/min
Work Speed 100 mm/min
Power 100%
And several passes and pass depths as shown in the picture
I first ran the upper group of rectangles. then I calibrated again the focus (bottom) and ran the second group of rectangles (middle). The very same piece of wood (I rearranged the image for convenience).
There is something weird on 0.4/20. I think that maybe the laser tube touched the surface and moved it. After 20 reps at 0.4 the laser head goes 8 mm down…
Hope some expert around will help with some hints…
joaquin
There is something weird. Do you have a enclosure?
You calibrated the focal length automatically?
It seems your focus was not proper at the first square, because there is no laser line.
May try to set the focus manually and try again, it could not be that there are focal lines in one pass and no lines at your square.
The positions with a blue X were not ‘lasered’. I though they were not relevant. Luban only allowed me to program 10 rectangles so I skipped those with the extreme parameters.
Sorry for not being more clear in the first place.
And…
yes, I have the enclosure. And focus calibration was made automatically some days ago. I only modify object thickness each time (in the posted example I did a new calibration between the two runs and results are identical). I have engraved white cardboard and wood sheets (to reproduce photographs) and results were excellent.
I’m with you on the smaller step down. I agree, logically it doesn’t make sense, but it does seem to work!
I have some 3.5mm ply I’m trying to cut, which while I know is beyond what’s stated as possible, it is more like 3mm soft wood with very thin veneers either side. The glue I don’t think is a problem with this stuff as it cuts through the first glue layer like butter.
I was trying 4, 5 and 6 passes with 0.4 - 0.6mm step downs, and there were only one or two that just about marked the bottom surface. After reading this post, I tried with much smaller step downs and found 0.1mm to be cutting deeper. 6 passes at this was almost getting through, but doing 8 or 10 didn’t seem to make any difference. So I figured the laser just couldn’t quite reach that last bit efficiently enough (hence the 3mm maximum cut).
But now I have tried running the cut a second time, and that seems to get through it just fine. I wonder if the laser doesn’t quite clean out the cut fully so after a few passes there’s some gunk stopping it from cutting properly, but going over the same cut a second time cleans that out leaving it able to make the final cut??
I’m going to do some final tests with this later to double check it works, and will post results once I’ve got them.
My theory for the smaller step down is as follows. But I really don’t know what I’m talking about, so may be complete and utter rubbish!
OK, so maybe I take all that back and say it is definitely down to the glue.
What was going to hopefully be my final test cuts, didn’t go all the way through, even though the same settings worked before on some smaller tests. But, I tried turning the wood over and cutting from the other side, and the same files did go pretty much all the way through! So I guess I just have uneven plywood, with thicker/stronger glue on one side (the outer plies are the same wood, they just look different in the photos for some reason).
For reference, those were 120mm/m all at 100%. 3/4/5 passes with 0.1mm drop down, followed by another 3/4/5 passes the same.
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