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mitch scherer
04-06-2010, 1:55 PM
Hi All

On a typical 18x24 laser bed with a 45W laser cutting through 1/8 in ply,
how much warp can you get away with without having to make multiple
passes?

Ross Moshinsky
04-06-2010, 2:23 PM
Hi All

On a typical 18x24 laser bed with a 45W laser cutting through 1/8 in ply,
how much warp can you get away with without having to make multiple
passes?

Test it and find out. It really depends on how high your tolerances can be. If it needs to be perfect, no amount of warp is acceptable. If it's just normal, auto focus to a low point and it will burn through whatever is closer to the lense. Get the plywood as flat as you can using tape. You can also make a vacuum table which will really work well.

John Noell
04-06-2010, 3:16 PM
It also depends on focal length of your lens. A longer focal length means more depth of field (and vice versa).

Lee DeRaud
04-06-2010, 5:34 PM
I realize your question is, "How much warp can a piece of 1/8" ply have and still be laserable?" But the only two properties that make plywood worth using are "strong" and "flat", and it sounds like the stuff you have is one short of its quota.

Maybe the question you should be asking is, "How much warp is acceptable before you change suppliers?"

Michael Kowalczyk
04-06-2010, 6:24 PM
It depends on who you get it from, if it is GENUINE Baltic Birch, humidity levels, grain, what is acceptable by you or your client and many other factors.

We use B/BB GENUINE Baltic Birch 3mm ply and once we cut it to size, it is wrapped in Kraft paper and stacked to keep it flat and minimize humidity seepage. If you are concerned about warpage, I would suggest you use vertical grain because it will lay flat when cutting small parts. Horizontal is good for LaserBuzz wall tributes (you only cut 2 large pieces and maybe some small glue shims) or items longer than 12" to maintain strength.

PM me if you want more info

mitch scherer
04-07-2010, 8:51 AM
Thanks Lee,
But I was told that even a 1/16 inch deviation in flatness across a 24 inch length of material would cause problems by not being able to cut through in one pass because it would be out of focus. I don't know where you get your ply but if you can get anything that does not deviate by 1/16 over 24 inches I'd like to know your supplier (and how much it costs for that material).

mitch scherer
04-07-2010, 8:53 AM
Thanks Michael!,
Can you tell me what material supplier you use?

Phil Thien
04-07-2010, 9:02 AM
That is pretty thin stuff, can't you use some double-sided tape to take the bow out?

Mike Null
04-07-2010, 9:10 AM
Mitch

Michael is a supplier of good quality BB plywood. Send him a PM.

I have a dozen or so sheets remaining from an order I placed several months ago. All are relatively flat (1/16" to 1/4") bow. A small weight will flatten these and allow even cutting.

Mine are stored in the basement here in St. Louis where humidity can soar.

Lee DeRaud
04-07-2010, 10:20 AM
But I was told that even a 1/16 inch deviation in flatness across a 24 inch length of material would cause problems by not being able to cut through in one pass because it would be out of focus. I don't know where you get your ply but if you can get anything that does not deviate by 1/16 over 24 inches I'd like to know your supplier (and how much it costs for that material).1. Don't believe everything you hear. Think it through: even if your 1/8" material is zero-tolerance flat, the beam is at least 1/16" out of focus at some point in the process.

2. www.aircraftspruce.com (http://www.aircraftspruce.com)

(And yes, I admit I'm blessed by living in a civilized climate.:cool:)

Richard Rumancik
04-07-2010, 11:16 AM
Mitch, you can change suppliers, store flat, store it in humidity controlled conditions, add a weight, and try all sorts of things - but in my opinion, warp happens . . .

You will still need a way to deal with it when you get a less than perfect sheet. If you are cutting many parts on the sheet, one strategy that I have used is to set up my pattern, then do a cut or two to relieve the stress in the sheet. Focus the best you can, and make the relief cuts. They could be in the form of a "+" or even a single line, depending on the warpage/bow direction. Or it could even zig-zag a bit between the nested parts. Just cut it so the sheet does not separate completely (say 1/4" from the edges.) The sheet will usually relax in the center and you may find that the overall flatness is quite tolerable. Refocus after the sheet relaxes.

I realize that this takes extra laser time, but 1/8" plywood is what it is. You can spend lots of time looking for the perfect supplier and get a good shipment once, then find the next lot warps. Figure out how to deal with the warped sheets as best you can.

I have found that tapes do not adhere well to plywood. Even if it SEEMS to stick it can still release half way through the job. Then you have scrap.

mitch scherer
04-07-2010, 1:02 PM
Thanks for all the help!
I am sure I can find a way to weight the material down or cut and refocus as Richard suggested!

Have a Great Day!

Michael Kowalczyk
04-07-2010, 1:07 PM
Thanks Michael!,
Can you tell me what material supplier you use?

Hey Mitch,
I could tell you but then we would have to take a long walk out to this abandoned quarry :eek:. Just kidding. Like Mike Null said (Thank You;)) this is something I offer to fellow laserers (is that a word) that use LaserBuzz Software (like we do) or for anything they want to laser like keychains, ornaments, gifts, etc...

Let me know if I can help. Also fill in your user profile info so we know whereabouts you are and make your signature so we know what laser, software or other equipment you use to help everyone help you.

Thanks and ...