Warped Plywood

[Robert Edington]

I'm new to lasers and Lightburn and everything (CAD) associated with it. I have no experience with any of it. I've had my laser about six weeks. It's fun to fool around with. I made some of those thunderlaser Eifel towers. On some of them I had to spend half an hour punching out tiny pieces of wood that didn't cut because of loss of focus due to warped plywood.
I've thought and thought about how to fix it. Trouble is, sometimes it's too high and other times it sags. I needed something that would hold the ply flat. Keep it up and keep it down.
I sat down with a pencil and paper and sketched out what I thought might work. Then I opened Lightburn and tried to draw it. Everything worked. I cut a prototype and it worked and the fit was pretty good. I haven't seen another type of fixture anywhere to try to fix this problem. I know it's wood but keep it out of the line of fire and it'll be alright.
They are made for 3mm ply or acrylic. I use a 20mm rare earth magnet to hold it to the steel plate in my bed. I have metric forstner bits so I drilled a 2mm deep hole with my 20mm forstner bit for the magnet to sit in. That improves it's holding strength.
I also made interior stands to prevent sags. These don't have the birdsmouth on them. They are the same height as the bottom of the slot.
I'm sorry the pictures are sideways and so large. This is my first attempt at a post with attachments.
I know it's pretty basic and simple, but it is my first stab at design and creating.
lightburn file attached
RP

[Pete Cyr]

https://cartonus.com/laser-tips-tricks-fix-materials/

Check out this link for another approach

[sebastien laforet]

best low-tech solution is to have a nice lot of wood in reserve, and store them flat with an heavy weight on top to prevent warping.

when/if your ply is warped, it WILL move when being cut, whatever you do to put it flat on the bed.

[Dan Torrey]

I laser quite a bit of 3mm Baltic birch plywood. I try my best to store flat with weights to try and take the warp out of it. I have tried several different methods to flatten out the material on the laser platform. The best solution for me so far is magnets. I purchased them from harbor freight, 2 ceramic magnets 7/8" x 1 7/8" x 3/8" for $0.99. The have a 5# pull which seems to be enough to flatten out the plywood. This may not work for everyone but if your platform is steel its worth a try.

[Riido Oun]

I use little pins (viewtopic.php?f=113&t=5147) to flatten out 4mm plywood. Works quite well. But this method can be used only with honeycomb table.

[Don Teeter]

This is a serious problem for me and I like these creative solutions. But I don't get how the pins in the honeycomb are held in tightly enough. Just make them the right dimension for a friction fit?

I try to use magnets but they're not strong enough to pull 1/4" (6mm) wood to the table. Stronger magnets are tall enough they risk being banged into by the laser head or the gantry. I've considering getting some strong electromagnets, but first need to experiment to figure out how strong the pull has to be.

[fred ungewitter]

I ran across some broad head bolts and wing nuts in my collection. The bolts fit perfectly through the honeycomb and washers on the wing nuts on the underside provided substantial grip.

Unfortunately, the honeycomb does not withstand very much force perpendicular to the bed. Some of the "weave" pulled out of line and had to be convinced to get back in bed.

I've since removed the honeycomb and dropped a flat sheet in its place. My magnets have much more grip on the flat steel than it did on the honeycomb edges.

[Jeffrey Aley]

This is a serious problem for me and I like these creative solutions. But I don't get how the pins in the honeycomb are held in tightly enough. Just make them the right dimension for a friction fit?

I try to use magnets but they're not strong enough to pull 1/4" (6mm) wood to the table. Stronger magnets are tall enough they risk being banged into by the laser head or the gantry. I've considering getting some strong electromagnets, but first need to experiment to figure out how strong the pull has to be.

Or you could use a lens with a greater depth-of-field. The spot size would increase, and you might need a new nozzle, but it might be suitable for some jobs. I think 4" Focal Length lenses are commonly available - ? Russ did a video on lenses and depth of field. But I don't recall which one.

[scott martin]

But I don't get how the pins in the honeycomb are held in tightly enough. Just make them the right dimension for a friction fit?

I use the same pins. The design of the pins causes it to contract and flex to fit in the honeycomb tight.

Here is a file to use. Just increase or decrease the size

y pin aeon.rld

x pin aeon.rld

[David Borneman]

I know this is an old thread, so this may not be helpful...

I live in a very hot and humid environment (Thailand), where the temp is always around 27-32c day and night, no matter the time of year, with 75%+ humidity.

My shop is not open aired, but it is also not air conditioned (in the workshop area) due to the number of exhaust fans we have running - AC is just not possible.

We had an issue with our wood (3mm ply) warping within hours of delivery. Our response was to set aside a room in the back with a dedicated air conditioner set to "dry" mode @ 27c (not really cooling, but it usually was cooler in there than the rest of the shop), and placing the wood in that room for just a few hours was enough to remove the warp and flatten it. We moved all our material storage to that room, which has pretty much fixed the issue for us (and we cut full sheets, so a small warp can be a big problem!).

On those occasions where there is a little warping, we simply tape the wood down to the bed slats with masking tape just before starting the cut. That usually works for us...