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Hi folks
I have a rosewood back and sides that I pulled out of storage to find that both back panels warped. They are cupped along the vertical grain. Wondering if there is a remedy for this? Does this mean the wood was improperly dried or did I store it incorrectly? This was going to be for my first acoustic build... Thanks for your input!

Not sure what you mean or how bad. I have this to say. If there is wax on the ends, do not use heat to flatten the boards. Wax will melt and flow like water into the wood and cannot be removed by practical means. I had good results with severely warped BRW backs and sides by immersing in water for a long time--at least a week, but maybe longer. Eventually the wood relaxed to the shape when it was sawed. Then I stickered and weighted it and let it dry a long time.

Trim the end grain by 1/8-1/4" (removes the wax), scrape any excess wax off surface, warm in oven to 160-180 deg F (use a ramekin or other heat-proof cup to hold one or two wet paper towels to keep things hydrated). Remove from oven after an hour and sticker between sheets of 3/4" ply, then weight top sheet with gallon containers of latex paint, cinder or concrete block, or weight set plates/dumbbells. Allow to cool to shop temperature overnight. Covering the ply with some kraft paper will keep the ply clean and suitable for reuse.

We've done this with BRW, coco, and EIR...the more resin-rich the wood, the less likely a second treatment will be needed.

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For the times they are a changin'

- Bob Dylan

Awesome! Thanks so much!

Often times this happens when there is one side of the wood exposed to air and so it dries at a faster rate. if you sprits the opposite convex side with water it might just flatten out for you. If I determine that a back set has a tendency to cup in one direction then I will brace that side along with the arch of the back.

Sticker it and see if it fix itself. Or wet the concave side and sticker.

I find when I resaw stuff from a billet it likes to cup. If it's thin enough I would just clamp it flat and plane it as it is... unfortunately not all wood is stable and especially for those dealing with figured stuff, they're often never stable.

Sometimes the cupping goes away by itself after enough time (say a couple of months) has passed, other times you have to take direct intervention like soaking it in water... Or you can always try steaming it flat (but make sure the wax is gone first). Other times you can just place the board concave face down on the floor and it fixes it as well.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

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If it has warped badly, then you don't want to force it flat just yet. Wipe down the interior concave surface with a damp cloth. The idea is to reverse the cupping and make the set flat again. Once it is close to flat, then sticker and let it acclimate to your workshop.

Thanks for all the input, was afraid this blank was ruined but now I'm optimistic I can get it back to flat.

This may prove useful too.
https://www.youtube.com/watch?v=0emWxl67tF0

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Gosh, no wonder why that wood warped! I'm not one to criticize Dan, or anyone really, but I'd never build with that set.

I woudn't use the EIR set in the video either, but I have joined a few sets that had a modest warp. I would recommend first minimizing the warp using the techniques described in the earlier posts.

The clamping set-up Dan used looks serviceable, but I've found a go-bar deck works better for me. I like to be able to see the joint, and the squeeze-out, when I clamp it. In the deck I run the bars along either side of the to hold the wood flat. To press the wood together, I keep one side from moving laterally by setting it against a piece of wood held down by go-bars. I press the other half in toward the joint using a row of four 1.5" discs of wood screwed to the go-bar deck, with each screw run through the disc off-center. These sound a lot fancier if you call them eccentric cams. Turning each cam presses the wood in toward the joint. With a good joint, all you need is firm, even pressure, and this set-up provides that. I can't remember where I read about this approach, but it's worked well for me.

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Tim Allen
"Never hurry, never rest."

Thanks for this posting this Tim.
I used to use a similar eccentric cams method for jointing (with weights, not gobar deck) before moving over to nails/wedges, and it worked well.
This sounds like a very sensible approach to jointing modestly warped panels.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

One thing I noticed was Dan was using an extra bearing or two on his top bearing router bit. Does anyone else do that?

Also, Dan did not show the joint being candled. Just looking at the joint while the wood is lying on the workbench is insufficient for a really tight joint.

I'm surprised nobody asked how cupped is it? If it is less than a 1/4" over the width of one of the pieces of the back then I wouldn't worry about it. In other words if it is relatively easy to flex it flat then I don't find them a problem to work with. I just joined a Honduran rosewood back set that was cupped about 3/16" on each piece. It wasn't very hard to hold it flat on the shooting board while I trued the joint (for sure check them with a back light) then glued it in an LMI jig that holds it flat. I also used 3M 233 tape to hold the joint together before I put it in the jig, I stretched about 5 pieces across the joint and then ran a piece of tape down the middle of the joint, opened up the joint, put in the glue then closed it and put it in the jig - belt and suspenders I suppose; not something I do if the back/top pieces are perfectly flat.

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Steve Smith
"Music is what feelings sound like"

It has mostly flattened out now after spraying a bit of water and it is stickered. Regarding Steve's post above about working with it slightly warped, I am curious how you would reliably thickness plane it if the board is warped. Gluing the two halves seems self explanatory but especially since I do not have a drum sander available I am going to have to figure out how to thickness plane by hand. Seems like it would be a lot more complicated on a warped board.

Good question about thickness planing, might not be easy. I do have a thickness sander so for slightly warped wood that flexes easy the rollers on the sander flatten the wood as it goes in. The moisture trick is good and I've used it before when needed. Glad your wood is mostly flat now.

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Steve Smith
"Music is what feelings sound like"

Good video Colin. Proves once again even old dogs can learn new tricks!

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Joe Beaver
Maker of Sawdust

My first thought is to use template tape to stick it to a flat surface and then use a large sanding block over the whole piece. This is going to be an issue for the back, sides and top since I really don't have a good way to thickness plane thin boards. This project is in line behind a whole bunch of other projects so I guess I have time to think about it .