Alternating grain to avoid cupping - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 11-24-2012, 02:42 PM Thread Starter
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Alternating grain to avoid cupping

Hi guys,
I just joined so do tell me if I have to do an introduction or something first, don't want to annoy the mods :).

I'm about to start a new project of a tv cabinet, its quite large and has a wine rack and whatever else built in. When I was selecting my boards I made sure they were all wider than the carcass (450mm) so I could rip them up the middle and re-glue to ensure they would be stable. I wasn't planning on flipping the board to alternate the grain because there was going to be 5 shelves over a 1500mm span rebated and glued in which I feel would keep the gables stable. I am beginning to have second thoughts though. Hopefully someone can help me out.
Cheers
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post #2 of 10 Old 11-24-2012, 03:34 PM
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Yes that is good to prevent warpage. It would also be helpful to select boards that were cut from the outer part of the log. Looking at the end of the boards you can tell the difference by the angle of the slope of the grain. The sharper the angle the closer it is to the center of the log.
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post #3 of 10 Old 11-24-2012, 03:54 PM
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+1 with Steve's reply.

You do not state whether you are using hardwood from a dedicated lumber yard or construction lumber from a big box store.

There can be a big moisture difference between hardwood and construction lumber. Both sources can be very different moisture levels than your shop/house.

There are many threads about people having cracks, or warpage either during construction or afterwards.

The alternate grain can help, but it will not prevent all potential problems is the average moisture of the air in the eventual room is very different than the average moisture content of the wood when purchased.

Whatever the source of the wood, it is recommended to allow the wood to sit in your workshop for a couple of weeks to get closer to the moisture level of the air in your shop.

If warpage/cracking happens in a board, it is annoying and may be an expense to replace the board, but better to do so before assembly of the project than afterwards.
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post #4 of 10 Old 11-24-2012, 05:25 PM Thread Starter
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Thanks for the replies guys.

What I really want to know is am I tempting faith by not alternating the boards or will the rebated shelves keep it stable?
Im using oak and they are quite wide boards about 700mm so Id say they are quite close to the center of the tree.
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post #5 of 10 Old 11-24-2012, 05:27 PM
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Regluing the board will do nothing to stabilize the wood for cupping. You still have the exact same grain structure as you did before. The only reason that I do this is because my jointer will only go up to 8". Flattening the board and applying equal finish coatings on both sides of the wood will do best to keep things stable and not cupping.

Using quarter sawn wood will help keeping the wood stable. Using plywood of the same species for large pcs will keep things flat and true.

Measure Twice Cut Once -- It's a lot easier to cut more off then it is to cut MORON.
Finishing is 3 parts chemistry and 1 part VooDoo http://lrgwood.com
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post #6 of 10 Old 11-24-2012, 05:32 PM
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I recently experienced some warping in hardwood boards ( ~6" wide) that I had flattened on a jointer and planed to thickness. I was baffled. Turns out I didn't allow the wood to acclimate to the relative humidity of the shop and it just took off.
More recently I milled a pile of cherry, but let it sit in the shop for 2 weeks before working it. It's been sitting for a couple weeks now - through a weather change or two as well- and is still straight as an arrow.
I always alternate the direction of the growth rings when I glue lam panels. Idk how important it actually is, but I've never had one warp (yet) so I keep doing it ;-)
Good luck on your build! Don't forget to post some pics!
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post #7 of 10 Old 11-24-2012, 06:31 PM
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I've done it both ways. Design wise alternating the grain could change the visual appeal. For wide boards, cutting in half or thirds may not solve the E&C possibility, as the width ends up the same if they are all glued together.





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post #8 of 10 Old 11-24-2012, 09:27 PM
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Leo is correct. Boards cup because of changes in the moisture content and the difference in dimension change radial to the log vs tangential. Avoiding the parts of board that have tight or smaller radius curves in the end.
The old question of alternating the curves or not keeps coming up. It the alternated boards are wider than a few inches, you can end up with a wavey board if there are moisture changes. This is not noticed if each is only 2-4 inches wide. Leaving them all the same way lets you fasten the wide glued up board in such a way that it can't cup. This only works if the boards are less than 3/4 inch thick or so. Wider boards have too large of forces to hold in all but the most rigid structure and strong fasteners.
Finishes slow down the process but can't stop it.
Letting machined boards stabilize lets you see possible issues and machine them out prior to final dimensioning. This is important if the wood has been in a shed or more humid environment or if you resaw thick boards to thinner ones as the interior may not have equilibrated or let some unknown drying tensions relieve.
Enjoy
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post #9 of 10 Old 11-25-2012, 04:45 AM Thread Starter
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Thanks for all the replies.
I think I will stick to my original thought of not alternating the grain and keep it much more astheticially pleasing.
I will post pics when its all done and fingers crossed it will still be a rectangle. :)
Cheers
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post #10 of 10 Old 11-26-2012, 12:06 AM
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Quote:
Originally Posted by Midlandbob View Post
Leo is correct. Boards cup because of changes in the moisture content and the difference in dimension change radial to the log vs tangential. Avoiding the parts of board that have tight or smaller radius curves in the end.
The old question of alternating the curves or not keeps coming up. It the alternated boards are wider than a few inches, you can end up with a wavey board if there are moisture changes. This is not noticed if each is only 2-4 inches wide. Leaving them all the same way lets you fasten the wide glued up board in such a way that it can't cup. This only works if the boards are less than 3/4 inch thick or so. Wider boards have too large of forces to hold in all but the most rigid structure and strong fasteners.
Finishes slow down the process but can't stop it.
Letting machined boards stabilize lets you see possible issues and machine them out prior to final dimensioning. This is important if the wood has been in a shed or more humid environment or if you resaw thick boards to thinner ones as the interior may not have equilibrated or let some unknown drying tensions relieve.
Enjoy
Bob's answer is the best one on this thread, IMO.
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