A question about cutting or piercing a hollow form

[David Somers]

Morning all!


A quick question for you. If you were going to use your laser to pierce some wood, say in the wall of a thin walled wooden vessel, a vase perhaps, what would you put inside it to prevent the beam from affecting the far wall of the piece? Or is that even an issue given the short focal point of an engraver?


Thanks everyone!


Dave

[Richard Rumancik]

Even though the depth of field may be limited the laser can still create some unsightly burns quite some distance away from the focal point.

Depending on the geometry there may be many ways to absorb the reming beam energy. You might be able to slide in a piece of anodized aluminum to block the beam on exit. Maybe even scrap wood would be fine. Perhaps you could use sand or fine gravel in some cases. Anything that will absorb the beam and not reflect it. It would probably be best if there was an air gap between the beam exit and absorber.

[Chuck Stone]

given the focal depth, I think you'd be hard pressed to do piercing on a vessel
unless it was all in a straight line around the center. Plus, once you turn it to the
final thickness, are you going to want to trust the laser for a test?

[Kev Williams]

If ever I need a shim, a test piece, a machining cut-thru base or a sacrificial laser backstop, I just use scrap plastic. I have enough scrap engraving plastic around here to fill the bed of a full size pickup truck-

[Joe Pelonio]

I remember a really tricky job I did cutting a logo out of nice wooden 4" square boxes (open at the bottom) that had orange painted insides. There were 100 of them, for display at shoe stores. I applied transfer tape to the top to protect the finish and stuck a piece of 1/4" acrylic inside that absorbed the beam nicely. Had to replace it periodically as it got too close to going through.

[Dan Hintz]

Fill it half full with glass beads from the local craft store. The large beads will not go through (or get trapped by) the small piercings (assuming you're thinking small holes, not large), the glass will easily absorb the beam, and they will roll with the vessel and always protect the "bottom" opposite the beam entry.

[Bill Cunningham]

Tin foil... Aluminum foil..

[Dan Hintz]

Tin foil... Aluminum foil..

Bad for reflections... you want an absorbent material.

[David Somers]

Chuck,

So long as I have the Z height available I think I can deal with cutting around the piece. Sometimes with a rotary device (Cone end or chuck end more than double rollers.) I have been looking at various pieces and the rotary units and think I can come up with a modification that would do what I wanted. Beyond that, a manual rotator with an indexer on it would work too. Easy enough to make. So there are a number of methods I can come up with for work piece handling. In terms of being willing to trust the laser....so long as I am not using some honking expensive piece of wood a mistake is annoying, but not horrible. Hollowing a piece to between 1/8 and a 1/4 inch thickness doesn't take that long. We will see though. I will do some runs with another persons laser as tests before I commit dollars to one of my own.

Dan, the glass beads are a great idea. Thanks!

Thanks for the thoughts everyone! Once I actually do some tests I will show the results and relate experiences. Taking me some time to get there. This working for a living thing sure gets in the way doesn't it?

Dave

[Rodne Gold]

We did a job where the laser had to pierce 4" diameter acrylic tubing , got a mark in the inside of the opposite wall , I just stuck in some steel wool and hey presto - no issues..

[David Somers]

Rodne! Thanks!! The steel wool is a great idea, and lighter if I happen to be using some sort of makeshift work hold. I keep a slug of 0000 around so that is easy.

Dave

[Dave Sheldrake]

Fill it half full with glass beads from the local craft store. The large beads will not go through (or get trapped by) the small piercings (assuming you're thinking small holes, not large), the glass will easily absorb the beam, and they will roll with the vessel and always protect the "bottom" opposite the beam entry.

Cracking idea Dan, the glass with scatter just about anything of any power into the scenery and as you say always be in the right place to work.

cheers

Dave

[Glen Monaghan]

If you are going to use steel wool, I'd suggest going with something very coarse, not really fine like quad-aught... Heat from a magnifying glass, a bit of current from a 9V or even strong 1.5V cell, or a spark from a steel striker can readily ignite 0000 steel wool. So, I'd be worried that heat from the laser beam could do the same. Once it gets started, steel wool burns a bit like a sparkler...

[David Somers]

Glen!

Well....I was wondering about that and although I don't have a laser here to try it with, I did just try a small torch. The kind you would do a Creme Brûlée with? Darned if the steel wood didn't take right off. I just sat down to pass that on!!! Glad you got this out first!!! Course steel wool didn't have any problems, at least with the torch. I think I will go back to the glass beads. That seems safer!

Thanks everyone!

Dave

[Chuck Stone]

Chuck,

So long as I have the Z height available I think I can deal with cutting around the piece. Sometimes with a rotary device (Cone end or chuck end more than double rollers.) I have been looking at various pieces and the rotary units and think I can come up with a modification that would do what I wanted. Beyond that, a manual rotator with an indexer on it would work too. Easy enough to make. So there are a number of methods I can come up with for work piece handling. In terms of being willing to trust the laser....so long as I am not using some honking expensive piece of wood a mistake is annoying, but not horrible. Hollowing a piece to between 1/8 and a 1/4 inch thickness doesn't take that long. We will see though. I will do some runs with another persons laser as tests before I commit dollars to one of my own.

I think a rather narrow band around the center should be pretty straightforward. But as you work
toward either side of center, the surface starts to fall away and you lose your focus. That means you
might have to look at doing your patterns in separate bands, raising or lowering either end of the
rotary device so your focus is maintained and your cuts angle in toward the center, too. In effect,
you'll be rotating on two axes, one handled by the rotary attachment.