Recurve limbs cupping

JamesV · November 25, 2017, 07:42:00 AM

What would cause the limbs on a newly built glass recurve bow start to cup? Over the years I have had a number of recurve bows that the limbs have started to cup shortly after building, in a matter of days. Limbs were straight when they were profiled, tape removed and braced the first time.

James

November 25, 2017, 08:11:00 AM

My only thought might be moisture in the lams before glue-up then curing in an oven where the wood would shrink... Do you know the moisture content of your lams???
Maybe someone that had this problem can help...

mikkekeswick · November 28, 2017, 03:29:00 AM

Poisson effect.

bamboo · November 28, 2017, 05:31:00 AM

are you positive they were flat with the tape on ?
it could be mimicking the hose shape

Bowjunkie · November 28, 2017, 05:56:00 AM

What Mike said. It's the result of the limb being flexed/compressed. Take a 1/2" thick piece of rubber, say 2" wide and bend it. It will cup noticeably. Bow limbs, especially wide thin laminated recurve limbs, just aren't able to go completely back to being flat again after. I've seen this residual cupping on virtually every recurve I've refinished. You can't just sand the finish off with a flat sanding block without thinning the glass along the edges.

JamesV · November 28, 2017, 09:42:00 AM

I think Shredd is right, that moisture in the core is the problem. The cupping I am talking about is severe to the point that I had one bow that the poundage went up almost 5# within a few days. I use a heavy pressure strip over the limbs to keep them flat during curing and they do come out of the oven flat. I have only had this problem with bamboo cores. I do have a moisture tester and I am going to start using it.

James

November 28, 2017, 03:55:00 PM

A cupped limb may give you a faster Bow...

Recurve limbs cupping

JamesV

mikkekeswick

bamboo

Bowjunkie

JamesV