[drepetto]

When I'm cutting through certain materials (plywood, MDF) I sometimes don't make it quite all the way through every time. So it's a real bummer when I pick up the piece and realize that it's not coming out! I've had some luck recently with very careful registration and cutting both sides, but that's laborious and prone to error. Does anyone have tricks for verifying that a cut went all the way through before picking up a piece? I've tried shining a bright light into the kerf, but that's pretty ambiguous on wood where the kerf is really thin. I've also thought of having the material floating off the bed a bit and shining a light underneath, but I'm skeptical that it would be bright/even enough to really show through. Often you can see the pieces pop out a little bit, but again, I find that with some material and especially with large, complex shapes, they tend to not move even when the cut goes all the way through because there's a lot of friction given the thin keft.

Any tricks/tips?


best,
douglas

[wontpontificate]

First off, I'd like to figure out why things aren't cutting all the way through. There are a lot of variables here that could affect your performance. A bit more information is necessary to isolate things:

* What sort of machine are you running? What's its power? What are you running it at?
* What is the thickness of the material you're trying to cut through?
* Do you have an air assist?
* What cut speed are you running at?

as for verifying if a cut went all the way through, make sure you're cutting from the "inside out" (i.e. make sure your cut order cuts out the detail in your stock before cutting the outline to let it "fall" out)

Though, I'd be more interested in figuring out why things aren't cutting through consistently first. Some possible problems (solutions):

* Smoke from the cut fouling the beam. (happens without air assist)
* Laser power is not optimized for cut speed (Adjust power or cut speed)
* Material's thickness exceeds focal plane of the laser (cut in multiple passes, adjusting Z distance between passes, or choose a thinner material if possible.)

Hopefully this helps!

-C

[Exsecratio]

Plywood is notorious for having these problems.It's caused by hard filler in the core of the 3 plys. If you notice any crackle or brighter than normal areas when the beam passes over it's likely to be bad cores in the ply (or knots)

cheers

Dave

[drepetto]

Hi wontpontificate, thanks for the info.

I'm running a 60watt Chinese machine, about 5 years old now. I do have air assist. I cut lots of different things at lots of different speeds. I often get pretty tweaky with different speeds/powers for different effects, better edges, etc. So it's not a particular problem with a particular material. As Dave mentions I often have the problem when cutting plywood, or for example, doing multiple fast passes on MDF to get a cleaner/less charred edge. MDF seems to hit a point where more passes won't actually do anything, and whether I'm through all the way depends on the source of the MDF and the complexity of the shape. So I'm not really asking about how to cut all the way through things, it's more that there are some situations where I just don't know for a given run whether I'll make it all the way through or not. I could keep doing additional passes all day long, but at some point I have to just hope it's through! Often I can hold down the work and poke around to see if the material flexes a bit, and that lets me know that it's free. But as I mentioned, with very complex cuts there's so much friction in the thin keft that even that's not a reliable indicator.

Maybe I'm just stuck with it! Luckily I've gotten quite good at flipping the piece and re-registering the cut so that I can do a finishing cut on the opposite side. But that takes a lot of time!


best,
douglas

[wontpontificate]

MDF seems to hit a point where more passes won't actually do anything, and whether I'm through all the way depends on the source of the MDF and the complexity of the shape.

Depending on the thickness of the MDF, I still wonder if you could make it all the way through by raising your bed slightly at the point when more passes don't seem to do anything, and get the focal point of the laser down in to the material, give it a little more of an advantage.

Thinking of ways to verify that it's through -- Does your machine have a front access hatch designed for oversized materials? Do you have a honeycomb/eggcrate bed?

If yes to both of these, an easy solution would be to grab a mirror and look up through the bottom of the bed to see if the cut made it through all the way. If you were crafty, you could stick a cheap webcam or security camera down there and monitor it while it's cutting too.

Hope this helps!

-C

[drepetto]

Ha, a camera! That's great. Somehow I never thought of that. I don't have a hatch on front that gives me access, but I think I could remove my honeycomb and use risers of some sort so that there's access underneath for a little camera. I have a GoPro with a live wireless image output, and I think that might just fit... GREAT IDEA, thank you!

As for the MDF, I do sometimes adjust the focus to cut deeper, but the problem with that is that the beam is wider as it's entering the material so I get charing on the top edges. That's usually exactly what I'm trying to avoid. It also often doesn't do much more than start to turn the MDF into charcoal. MDF in general is pretty terrible, but I'm stuck using it sometimes.


best,
douglas