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cupping wood - Back and top

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cupping wood - Back and top

Postby Cory Weinberg » Tue May 24, 2016 7:28 pm

I have a resawn top (Sitka Spruce) and back (Sapele) for my newest build. The wood has cupped. I wet the concave sections and pressed them for 5 days and although slightly reduced, they still present a signifcant challenge. I don't know what else to do to bring them back to flat. Any thoughts?
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Re: cupping wood - Back and top

Postby Chuck Tweedy » Thu May 26, 2016 12:50 pm

How "deep" is the cup??
Are the plates to final thickness??

In general, if the cupping of a rough set is slight (~ 1/8" or 4mm), then after you thickness the plates 1 of 2 things will happen.
1) The cupping will go away
2) There will be such subtle cupping, that you can just ignore it

Acoustic guitar plates are so thin that the braces will determine the final shape.
The problem comes when you can not uniformly thin the plates - in a sander, or with a plane.
If they will not flex back enough to be processed, then you are SOL
Likes to drink Rosewood Juice
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Re: cupping wood - Back and top

Postby Clay Schaeffer » Thu May 26, 2016 6:31 pm

If you have a bending blanket you could try clamping them between two flat pieces of wood and heating them much as you would bend sides.
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Re: cupping wood - Back and top

Postby Daryl Kosinski » Thu Jun 02, 2016 2:01 pm

Your wood could be case hardened from improper drying. There is no cure for case hardened wood.
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Re: cupping wood - Back and top

Postby Barry Black » Sun Jun 05, 2016 6:59 pm

Sometimes I have found that even quarter sawn wood will cup after resawing simply because the interior moisture level is different from the outside. To correct, I simply lay them on the cement floor of my shop, concave down , with some weight to hold them in place for a few days. This has never failed for me. When thicknessing, always take material off of each side to maintain the stability.
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