I ran a search for cutting gun case foam, but nothing related to my question came up.
I am starting to experiment with engraving and cutting the foam inserts for gun cases.
I’m getting good results with my 180w 50 X 36 laser with the engraving. When I want to cut through the 1-1/2" foam, the cuts look like the kerf is 1/4" wide at the bottom of the foam. The blocks coming out of the foam look the beam is changing direction. Some of the kerf bends to the left or right.
I switched to a 4" lens and still get the same result.
Could it be a speed or power setting that I might change to get straighter more vertical cuts?
What specific type of foam are you cutting. I’m assuming some sort of high density rubberized foam but specifics might be relevant.
I’ve had a recent epiphany about cutting foam. Materials like wood cut with a wider kerf at the entry surface than at the exiting surface. The understanding is that the wood fibers get vaporized by the laser. This makes sense for why the kerf would be wider at top than the bottom.
But as you have found foam behaves differently with a wider kerf at the exit surface. I think what’s happening is that the foam does vaporize near the top surface. However, the material toward the bottom is actually melting and contracting away from the center of the laser beam instead of simply vaporizing. This leaves a wider kerf at the bottom.
As for your specific situation it’s interesting because you’re saying it appears that the direction of the kerf can shift. That sounds like it could be due to irregularities in the foam itself. Either foam density or from air pockets. Or if the material is an aggregate of some sort.
Strategies for dealing with this I haven’t fully refined.:
One school of thought is that you could try to increase power to see if you can truly vaporize the material before any melting occurs. In contrast, I’ve found that reducing power to the minimum required leaves a more uniform look.
Additionally, if you’re okay with a stairstep look you could run multiple passes at very reduced power to dramatically reduce the size of the bottom kerf.
You could try cutting half-way through the material, flipping it over, and completing the cut from the other side
Try focusing at different depths in the foam; this hasn’t really worked well for me and also seems to affect top surface quality which is paramount for what I do.
I haven’t been truly happy with any of these strategies but have found the most acceptable results for my use to be to use the lower power required while cutting all the way through. The bottom surface quality isn’t nearly as important as the top surface for what I do.
When I first got the laser about 10 months ago, I went through a long process of trying to get everything aligned. I was cutting through 3/4" clear acrylic and made my adjustments of centering the beam in the center of the nozzle as well as making sure the cuts were vertical in all directions. When I started making adjustment, the cuts were looking like a parallelogram. Once the adjustments were made, the plug that dropped out of the acrylic sheet was vertical on 4 sides.
I’m pretty confident of my set up. I cut through 3/4" pine pretty regularly and all the cuts are vertical, even with a 2-1/2" lens.
In the foam, I can cut square holes, side by side. When I pull out the plugs that are left, no two plugs are the same. The kerf bends to the left on one side, bends to the right on the other.
In that case it must be something incompatible in the type of foam you have chosen. as this is the only thing in the setup that is changing. I cut foam inserts all the time with no issues. The foam I use is quite a firm density, I have tried cutting softer foams sometimes they work lovely and other foams tend to melt and have a sticky residy aroudn the cut surface, so I avoid these.
It must be the material the foam is made of, maybe the heat is shrinking the foam unevenly?
oh, the other this I do is really ramp up the air to quite a high pressure.
Right now, I am using the Pelican Case replacement foam inserts. It’s Polyurethane, open cell. I do have some other inserts coming made from some cross link Polyethylene. I want to give those a try to see in I have different results.
Yes, the cut at the top of the insert would be the most important part of the project, but there are cut outs that would need to get maybe 1/2 a thickness of foam placed back into the cutout so it wouldn’t need to be full depth. I planned on using the plug that came out, but with the bottom being so much larger than the top, it has too much slop.
I will try to run it at a lower power and a couple of passes, as well as ramping up the power too.
@LaserCuttingPro brought up a good point that I forgot about. Air assist can make a big difference as well. I haven’t explored this enough as I don’t have a high pressure air compressor. Perhaps higher air flow air assist and possibly a system of venting below the foam could help reduce the bottom kerf.
When I started experimenting the bottom kerf was about 4-5 times bigger than the kerf at the top.
I have added more air pressure, sped up the cut and reduced the power setting. I set it up to run 3 consecutive cuts.
I’m extremely happy with the results.
The cuts are now vertical, the kerf on the bottom is significantly smaller than before, there is less smoke and that slight residue that was left before is gone.
Thanks to everyone for all their suggestions and ideas.