I’m using a low power 5.5w laser to cut heavy (4mm) cardboard. I’ve tried high speed and dozens of passes as well as slower speeds with fewer passes. Both cases cause the cardboard to catch fire. What will work is if I do a single pass of the entire surface and then repeat that until I have a complete cut, it looks like I need 10 passes to ensure a complete burn through.
Is it possible to automate this in LB, it’s pretty much the opposite of optimization but it lets the heat dissipate before it hits the same area again?
It’s not necessarily the heat buildup causing the flames, the material at the edges has been scorched and is a lot more flammable.
Adding air assist would help a lot, others have done the same mod to those machine from what I have seen.
I have an air assist now, not high pressure but it does a decent job of clearing smoke away from the lens. What I’m seeing is that a small section of the cut will start to glow and before it can go out the laser is back on top of it keeping it going and growing. If the laser moves on to another area the ember goes out quickly and doesn’t hurt the project. I’m cutting 5mm plywood without problems and 3mm and thinner cardboard isn’t an issue, just this 4mm heavy cardboard.
Sorry, that last reply sounds like I’m blowing you off your response (pun). I’m going to hook up an air brush compressor and do some experiments. Thanks for the advice and I’ll let you know if it works or not.
In order to do a quick test I just held the compressor hose by hand and ran the project. It did improve the edges greatly and I didn’t have any flare ups. It’s hard to believe that adding oxygen to a fire is a good thing but in this case it really is.
Don’t think of it as adding oxygen, but more like blowing out a candle.
Good air assist puts such a high velocity stream of air in to the cut that no flame can possibly survive.
Pleeeease dont’t try this with oxygen! 
Oh where’s your sense of adventure? 
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It is rather counter-intuitive 
Cutting acrylic would be nigh impossible without the high air flow, unless you are looking for a way to void your house insurance 
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