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Preventing cupping without glue

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Forum topic by Rayne posted 12-19-2014 04:55 PM 676 views 0 times favorited 4 replies Add to Favorites Watch
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Rayne

470 posts in 1002 days


12-19-2014 04:55 PM

Topic tags/keywords: resource tip question walnut jointer plane tablesaw clamp

Hello LJ community, I am in the process of making some keepsake boxes like those of the Woodwhisperer. The keepsake box uses one dovetail joint to allow the top to slide back and forth and then held with a key. Well, I finished the base, so that’s not the problem; it’s the top. I cut the dovetail slot on a prototype and the lid cupped almost immediately, but it was on soft pine, so I expected that, but I wasn’t expecting it to happen so badly on hardwoods like walnut and some other hardwood that stinks a little. Right now, I have it clamped down flat on my workbench, but is there a way to prevent the cupping? The dovetail is cut with the grain, so that’s probably not helping, but it’s also the method Mark used. If I kept it clamped up, will the cupping stop at some point and stay flat when I release it? Or are there other methods to stop it from cupping? i’d appreciate any feedback. I get the feeling I have to redo the top and cut across the grain, but I’ll wait for some feedback before going that route. Thanks!


4 replies so far

View bold1's profile

bold1

261 posts in 1309 days


#1 posted 12-19-2014 10:16 PM

What you are seeing is stress in the wood. When drying in a kiln, you steam the wood when it’s dry to relieve the stress (conditioning). You check the stress by cutting prongs from your test boards. If your prongs move you need to condition your charge longer. You can try wetting or steaming to make the wood “plastic” again and clamp flat till dry. If your wood has stress in it your new pieces will still want to cup unless you relieve it.

View bondogaposis's profile

bondogaposis

4026 posts in 1813 days


#2 posted 12-19-2014 11:01 PM

Use quarter sawn material.

-- Bondo Gaposis

View bobro's profile

bobro

308 posts in 773 days


#3 posted 12-20-2014 12:33 AM

Prongs are sideways to the board and so you get a prong test willy nilly when you make a breadboard end, but a similar kind of effect is happening here- I agree that you should cut your dovetail across the grain and have the top pretty thick.

-- Lao Ma: You are so full of anger and hatred. Xena: Everybody's gotta be full of something.

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Rayne

470 posts in 1002 days


#4 posted 12-20-2014 12:44 AM

Thanks for the suggestions. I just clamped them flat, turned some fans on, and let it dry dovetail side up. For the most part, they are staying flat. I hope I don’t see them cup again in the morning, or I’ll use the heat / steam / wetting method.
Where I live, quarter sawn material is very hard to come by at an affordable price. I just have to deal with what I can get. :-/

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