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warp control

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Forum topic by Sherlock posted 12-29-2008 02:02 PM 1575 views 0 times favorited 11 replies Add to Favorites Watch
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Sherlock

11 posts in 3348 days


12-29-2008 02:02 PM

What are the elements of controlling warp? I have had several projects (mostly box lids) that I used good, cured wood that was good when installed, but, later warped afterwards. Recently, I cut several pieces from the same big piece that has been cured for years (cherry). After I glued them together, 2 of the 4 pieces warped while the other 2 didn’t. They were 1/4” thick slices.


11 replies so far

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Sherlock

11 posts in 3348 days


#1 posted 12-29-2008 02:51 PM

Thanks DaveR. I’m new at this and am still trying to figure out how all this LJ stuff works. I hope my reply to you goes thru.

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Kate

400 posts in 3781 days


#2 posted 12-29-2008 03:38 PM

The other thing you could do is make your box top either frame and panel, or with breadboard type ends, or, if you want to get fancy, use veneer (make sure and veneer both sides of your substrate).

Wood will move regardless of what you do, so the trick is to minimize the movement as with Dave’s suggestions, or you can let it move in such a way it won’t interfere with your design. The reason it warps is because the end grain absorbs moisture more quickly than the edge or surface. If you can make it so that the end grain is covered it will help with the cupping.

However you do it, you don’t want to glue the end grain of the top to whatever you are using to frame it. In the link above the first jewelry box has frame and flat panel doors, and the second box has a flat frame so it looks like one piece, but the ends are actually tongue and groove. It’s also glued up with alternating grain and is small enough that any slight opening of the top isn’t noticeable.

Hope this helps and good luck.

-- Kate, http://www.wooden-box-maker.com

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Moron

5032 posts in 3800 days


#3 posted 12-29-2008 03:47 PM

To add. Putting more finish on the side of the lid that is constantly exposed to the elements and less finish on the inside can cause wood to warp.

removing wood from machining can cause locked stresses to release in the form of warping

sometimes it doesnt matter what you do…................wood moves

Cheers

-- "Good artists borrow, great artists steal”…..Picasso

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Karson

35099 posts in 4307 days


#4 posted 12-29-2008 05:15 PM

The moisture content of wood might not always be the same across the piece. If you resawed the 1/4” slices then the resulting pieces might not all have the same moisture content.

If you have a 1” board and you want a 3/4” thick board and you plane most of the wood off one side then you have an unbalanced piece of wood. Thw moisture on the surface of the 3/4” piece is not the same because one was at the surface of the original piece and the other is 1/4” in from the original surface.

And then again wood moves. You do what you can to minimize the damage caused from the wood movement. Maybe I shouldn’t have said damage. Minimize the effects of wood movement. As Kate said above.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia karsonwm@gmail.com †

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PaulMarcel

3 posts in 3400 days


#5 posted 01-09-2009 10:25 AM

I think it would be helpful to know how you used the 1/4” wood since it almost sounds like home-cut veneer. If you did use it to veneer the top, you have to remember that typical wood glue contains a lot of water and that will swell the fibers on the face of the veneer slathered in glue. On drying (which will happen after the glue cures), that face will shrink and likely distort the substrate wood. This is actually why common wisdom says to veneer both sides: if you understand the water component, it makes sense and it also lets you veneer just one side, with a non-water-based glue such as Unibond 800.

If you resawed the wood, I’ve noticed that the resulting ‘halves’ of a board resawn in two cup towards each other, regardless the grain circles, like this: (). While I don’t have a lot of experience resawing, I have had the best luck flipping the boards, convex sides in… like this: )( and clamping them flat. If done right away, I’ve usually found 2 nice flat halves in the morning. At this time, I have 5 3/8” resawn boards of oak that were severely cupped and flattened as described. They have since sat on a table in the garage for 2 weeks during which we had typical dry days (Arizona!) and 3 all-day rains. YMMV.

-- Read my blog, please :) http://HalfInchShy.com

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Randy Moseley

111 posts in 3345 days


#6 posted 01-15-2009 03:05 AM

I’ve started using plywood with 1” to 2” solid wood mitered rails for lids. It never warps and the looks great.

-- Randy, DeKalb, Illinois

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childress

841 posts in 3448 days


#7 posted 01-16-2009 05:27 AM

And remember, just because the cherry is “cured” as you say, that doesn’t mean in won’t gain or lose moisture….wood always adapts its moisture contect to the environment it’s in. Where was the wood stored before and during the build (I know, the shop) compared to where it is after finished? Changing the environment will affect it.

Also, as Karson stated, the moisture content can be different across the board, so when milling or resawing a piece like that, it could have case hardening or reverse case hardening. Which is basically tension in the core of the piece and compression in the shell, or vice versa. So, to answer your question, controlling warp ultimately dpends on how the wood was dried and then how it’s stored.

I’ve had pieces that I laminated together warp or bow afterwards. That was when my shop was in a metal building with NO insulation and in the middle of summer. Where I live it gets over 100 and I’m sure even hotter in the shop. Well, hotter air can hold more moisture in it and the relative humidity was high…so the absolute humidity was very high, causing the wood to suck it up like a sponge too fast and warp. after bringing the boards to a more controlled environment (cooler and lest humidity) the boards flattened out and have been fine.

-- Childress Woodworks

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dsb1829

367 posts in 3534 days


#8 posted 01-16-2009 04:32 PM

Here are a couple of interesting entries with respect to resawing from the Heartwood Blog. They do show some of the moisture effects. Keeping moisture flow equal seems to be very important. I try to do all my milling in 1 shot and mill all sides so they all have equal breathing ability.

http://www.rpwoodwork.com/blog/2008/11/07/more-on-resawing/

http://www.rpwoodwork.com/blog/2009/01/09/resaw-rethink/

-- Doug, woodworking in Alabama

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Sherlock

11 posts in 3348 days


#9 posted 01-16-2009 05:09 PM

Hey, thanks to all you guys. I’m sure I can use all these tips to get better.

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Peter Oxley

1426 posts in 3781 days


#10 posted 01-16-2009 05:19 PM

Every time I see the title of this thread on the Pulse page I think …

“Well, first, make sure Scotty is in the engine room …”

-- http://www.peteroxley.com/woodworking -- http://north40studios.etsy.com --

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dsb1829

367 posts in 3534 days


#11 posted 01-17-2009 05:27 PM

that’s awfull :-)

-- Doug, woodworking in Alabama

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