Any tips on cutting settings for exotic hardwoods? looking to do some work with brazilian rosewood, and maybe zebrawood - also saw in another thread paduk(sp?) - very cool stuff. But I need to cut through without burning. I tried just a straight cut and at 100speed / full power / 2 passes it got 99% through but the edges were charcoal.
This is pretty well discussed. Search the forums.
The short version is that youāre in for a bit of a fight on both of those woods (for different reasons), especially at 1/4ā. Let us know if you still have questions once youāve researched it on the forum, or if you already have, then be a bit more specific, maybe?
I did find another threadā¦ would doing multiple passes at different focal lengths help? I mean once I get half way through, do another pass with the focus set to 1/8"?
Some people have had good luck with that, yes. Iāve not fooled with 1/4ā so Iām not the expert by any stretch ā I stick with 1/8ā pretty much exclusively. 1/8ā can be harder to find and maybe not as useful in certain products, but itās definitely easier to cut.
yeah it is! but this particular application - 1/4" is what it needs to beā¦
Iām a bit of a laser newb, of course, so Iām not sure if the focal length thing will really work wellā¦ will the āwallsā of the cut defuse the beam before it hits focal length? OY the conundrums!
Thanks!
The conventional wisdom is that changing focal depth keeps the kerf size down a bit and that the real enemy on thick cuts is charred material absorbing laser energy.
Weāre amateur scientists in a lot of ways so I donāt know if thatās precisely true; the laser/wood interface is really complicated from a physics standpoint, acting a bit like combustion and a bit like ablation. Add to that the fact that each species of wood behaves in its own ways: some are harder to cut, some char badly, some cut unevenly, etc. all of this is to say that itās s bit hard to definitively say how something works, but we can see empirical results, and it does seem to help.
Lucky you, rosewood is one of the hardest to cut (he says, not knowing which rosewood you have, there are lots and each has potentially different attributes. Iām guessing Bolivian which is a bear) and zebrawood is prone to char and also uneven cutting because of its striped nature.
Some people have reported better char reduction by doing lots of lower-power passes too. (Lots like up to ten). Search the forum for how to do lots of passes, you can manually override the three limit. (Or copy and paste in place your cutline in your file and re upload)
Lastly if you lose the char fight, depending on your design cutting the piece a bit large and sanding to size can eliminate that issue. If you need super precision thatās not going to work obviously, but itās an option.
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I had a glue up of five or six different wood species. Got it to go through everything except the mahogany. Nothing worked that didnāt give a nasty kerf.
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Method you used?
I got it working for walnut and zebrawood. duplicated the circle 3 times, set 3 different colors - imported into GFUI and did 3 different focals and speeds, 3 passes each. The only problem is that the laser starts/stops in exactly the same spotā¦ and seems to leave a bit of extra burn there? or is that my conception?
I recommend researching exotic woods before cutting. Many rosewoods, especially cocobolo, can trigger allergic reactions. Not sure if burning is the same as cutting and sanding but precautions should be made until you know for sure.
https://www.wood-database.com/wood-articles/wood-allergies-and-toxicity/
Thanks. Weāre well ventilated with a booster fan taking 120CFM out the windowā¦
That is correct. You may also notice this at corners, the point of a corner will be more well done. You can avoid this by rounding corners, if your design allows. The people who work on nice paper projects will use engrave instead of cut to cut paper. Cut and score are subject to an overburn that engrave is not, but engrave takes a lot longer.
It has been my observation that the glowforge will start and stop at a node. So if you open your design and see a node in the vector where there doesnāt need to be one you can delete it. Inkscape likes to add nodes in the middle of straight lines when a boolean or other operation is performed on an object. I could be wrong about the start and stop on a node, but it wonāt hurt.
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Overcutting outside corners has good results as well. You basically make a cross instead of a corner. You cut into the unused material a bit but you donāt have to overcut far. I have had good results with 1 mm.
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Ah, finally found the post that experimented with reducing overburn using paper:
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if you copy/pasted the 3 versions of the circle in place, they will each still have the same start/stop points. You could try rotating one of them 120Ā°, and one of them -120Ā°, that would give you three overburn spots but they would be evenly spaced around the circumference.
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I did. I used the inkscape duplicate featureā¦
Iāll try rotating them and see how that works!
It works in AI, I canāt promise it will work in inkscape, but I think it will.
Basically right! Every vector path has a start coordinate and an ending coordinate, typically with other coordinates in-between that guide you between them.
A simple example would be a square. It could mark the top left coordinate, the top right, then bottom right, bottom left, and finally back to the top left to close it out.
You could also reverse the path, which would go Top Left, Bottom Left, Bottom Right, Top Right, Close/Top Left.
I suppose if you had a symmetric shape, you could actually rotate or flip a second copy of the design and have starting points at different coordinates which could help burning at the initial pierce point for multiple passes.
Typically, in the CNC world, for a cutout shape where you need the interior and not the exterior, you would design in a lead-in and lead-out, which would result in a small overrun for the start and end points.
The other thing is to slow the laser head down and adjust power accordingly so you have less variation in speed as it approaches corners that the head has to slow down for.
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using slowed cuts (under 300) already. any slower and the char gets really badā¦
When i get back next week iāll take a look at the rotating the circles concept!
Iām not sure how youāre getting cuts at 300 on 1/4ā material; 300 isnāt slow at all. PG thick ply settings are down around 130āish.
lots of passesā¦ 
to keep the char down. zebra wood is a bitchkittyā¦