Lamination cupping?

[bdsmith1]

So I had some osage I cut lams out of for a bow I was going to work on tomorrow. I've got a full time job with a pretty irregular schedule, so I only get to work in the shop in spurts. Living in Georgia, humidity will get to thin cut lams pretty quick so I taped the stack together and put it in my dry box with a single indirect bulb that gets to about 100F to keep it from going limp until I could get back to work on it. . Unfortunately, the top lam cupped up on me. I'm debating on whether or not I can rely on the pressure hose to press this flat enough for good glue lines or if I should just toss this lam. I'm more concerned with preventing this in the future. I've never had this issue with ash, maple, or boo.  Have you guys had this problem and how do you prevent it.

[bdsmith1]

As an aside, This is the first time I'm using clear glass, which is why I'm working with Osage for these limbs. Any extra precautions or differences from using black glass? I've heard about letting it set in the form for 30 minutes prior to setting it in the hotbox, tho I don't know the reason.  I know I've got some sap wood on a few of these, but it's in the nock side and will get cut out. Will sap wood mess with clarity?

[simk]

I dont think you will have any problems. When I glue thinner lams with water based pva glue instead of epoxy the laminates quickly warp the same, while the endproduct is fine. The pressure of your airhose will flatten out everything, np.
Simon

[kennym]

Think it’ll be fine

I also air up in 10 lb increments roughly with a few minutes between

No idea if it helps lol

[garyschuler]

Have you thought about flipping the top lam and alternating in opposite grain configuration with #3 lam. Then putting those in the middle with the straight grained  pieces on top and bottom of stack. I like to alternate opposing grains to help even out twisting issues after glue up. Don’t know if this will help you, but good for thought.

[Kirkll]

Gary has a good point on those lams that have the grain running at 45 degrees. I think it would be wise to pay close attention to how those lay up and keep the opposing grains alternated in the center.  With osage i think it might make a difference on limb twist issues.

Good catch Gary....

[bdsmith1]

Thanks Gary, I wouldn't have thought about that!

[mmattockx]

No one has said anything about why that lam cupped in the first place. I would guess you taped the bundle together and then put in the box with that lam on top of the bundle. It was the only one exposed to air all along that one face, the rest were covered on both faces and only drying on the ends and edges. The exposed face dried more than the rest and it pulled in that direction.

Next time you put a bundle together like that put an extra piece of scrap on the top to cover that lam as well and you should minimize any cupping/warping problems.


Mark