1/8" Birch Plywood

[Stanley Waldrup]

I just picked up 20 sheets of 1/8" Birch plywood. Some of it has already warped up on me. I just cut 5 sheets into the 12x24 pieces and they are warping. What is the best way to keep the wood flat? Some say to store flat and I have heard of storing them on there side... Right now a have a large stack with 12x12 Tiles on them for weight....
And my second question is there seems to be spots where the laser will not burn all the way through. you can watch the laser get real bright in those areas. I am thinking it the glue in side the panel. Anyone else experence this? There don't seem to be any voids....
Thanks
Stanley

[Nancy Laird]

Stanley,

It's dry as a bone here in NM, and our 1/8" also warps. I don't think there's any way to keep it from happening, but we have resolved our issue with keeping the stuff flat under the laser.

David got a piece of flat aluminum bar - about 1-1/4" wide and 5-6 feet long. He cut it and attached it to the rulers on our cutting table both horizontally and vertically, so about 1/4" of it overhangs the table, and the 1/8" can slip under it. He made another piece, in two parts, that can move back and forth on the table and hold down the other end. It's quite an ingenious resolution to the problem we were having in keeping the material flat for vectoring. I'll take some pictures of it and post them, but can't right now because I'm running a job.

We had the problem of our self-stick veneer curling, so we have a piece of rail sitting on top of it, on a piece of 1/4" junk ply, to keep it relatively flat. Of course, when I start using veneer, it's a pain to move the rail, but it works to keep the stuff flat.

As far as the spots that won't burn through, that's just the glue. We have that occasionally also. Just take a sharp box knife and finish cutting it through and you won't lose the piece.

Nancy

[Joe Pelonio]

With warped material there are two things I have done that work. You can use a spray adhesive such as 3M "77" or a few bits of double sided tape to adhere it flat to a piece of sacrificial acrylic. Also, on the Epilog vector grid, you can loosen the ruler screws and tuck the edge under, then tighten. That one works best on a full sized piece of engraving laminate.

[Robert Ray]

That's the grief I work with daily. I almost only use birch plywood. I found that sanding both sides with 400 grit gets it smooth enough that the laser cuts cleaner with fewer fibers left attached. The sanding process somehow helps reduce warpage.

Also I set my driver (Laserpro Venus 35W) to 1000 DPI and 200 PPI for plywood. This gives the best results for cutting through stuborn fibers for me.

Here is my trick for storing the plywood... Flip every other sheet over in your stack and store horizontally. If the plywood is warped, then they reinforce each other's warpage. By flipping every other sheet over, you counter the warpage by turning the stack from a giant compound leaf spring into an accordian, and you compress the accordian effect flat with weights. I just stack about 3 sheets of 1/8" clear acrylic on to as weights.

Also, do not cut the plywood into usable sheet sizes until just before you are ready to laser them, do not set the wood close to your laser where the laser tube fans can blow over the wood or that side will curl up, and finally, take your wife's blow dryer (on air or cool only)to the outside centerline of a bowed piece working the center axis only, a few seconds at a time to take the warp out. Too much and it will distort or even curl the other way.

-Robert

[Michael Kowalczyk]

I just picked up 20 sheets of 1/8" Birch plywood. Some of it has already warped up on me. I just cut 5 sheets into the 12x24 pieces and they are warping. What is the best way to keep the wood flat? Some say to store flat and I have heard of storing them on there side... Right now a have a large stack with 12x12 Tiles on them for weight....
And my second question is there seems to be spots where the laser will not burn all the way through. you can watch the laser get real bright in those areas. I am thinking it the glue in side the panel. Anyone else experience this? There don't seem to be any voids....
Thanks
Stanley

Hey Stanley,
Where are you located? Do you have high humidity like we do in Houston?
We wrap our stock in kraft paper to keep humidity levels down. Robert's idea about flipping ever other sheet also works when the need arises. But you have to remember to flip it back to keep your project consistent. Even on a sheet of B/BB you will have a slight grain difference when you stain it.

What direction is your grain going? If it is horizontal that can tend to warp more but when it is vertical it almost always lays flat. So it will depend on what your project is and if it is grain direction sensitive.

I do not recognize your name so I can assume that you did not get your 3mm (1/8")ply from us. Is it true Russian Birch B/BB? Some Chinese stock that may have a poplar core is known to turn into potato chips because the core has so much humidity. It could also just be your environment. Any time you open a box and do not seal it back up or put some weight on top to keep the humidity out of it you will get some warpage. If you are not going to stain it then you may want to put a clear coat on BOTH SIDES. If you do only 1 side it will warp.

The part you say about not cutting all the way through can be one of two things-- #1 it may have a football or small pin knot there
#2 if it is doing it in say the X20Y9 area, it may be a mirror alignment. I have heard some lasers lose strength as they get further away from Home (X0,Y0).

Let me know (PM me) if I can help and...

[Richard Rumancik]

Stanley, Michael is correct about some plywoods being quite inferior. The sparks you see occurs when the laser hits a really hard knot in an internal layer. I used to buy some plywood and never saw that happen; now my customer supplies the plywood and it has all kinds of football patches both sides and lots of knots. When I cut a part and hit a knot it is usually history. It is very difficult to get it out of the sheet without damage and not usually worth it. For larger parts this can be expensive scrap. Also, the plywood I am getting now is usually quite warped. It is a lot of trouble to set up when the sheet won't lie flat.

In some cases it may pay to look for a better quality plywood and avoid some of the problems and rejects.