Focus the beam on Neje 30 w. Have I done it right?

[berainlb (PY)]

Was the cut made focused into the center of the material as implied in the diagram? If so, here’s my take on what I think is happening.

You might want to read a previous post from me that describes what I’ve recently discovered about cutting foam:

Cutting gun case foam

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…

1. The center portion of the foam is sharp and vertical with the paper walls because that’s where you focused the beam. The center portion is vaporized and leaves a small kerf.
2. The parts that are retracted are due to the unfocused beam not vaporizing but rather melting the foam. This causes those areas to retract.
3. The top and bottom paper layers don’t retract in the same way so are cut relatively cleanly and with little kerf.
4. I’m a little surprised that the bottom portion of the foam near the paper is not further retracted… as to have a wider kerf at bottom. I suspect what’s happening is that the paper below is somehow insulating the foam or perhaps acting as a heat sink to reduce melting. Or maybe just due to adhesion the foam doesn’t pull away as much.

Overall, I would have guessed this was a 2 pass cut but I think my explanation could work.