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Thread: Severe cupping
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26th January 2011, 02:35 PM #1
Severe cupping
hi Everyone, happy Australia day,
I have a problem I am not sure how to resolve and I put it to your infinite wisdom. I have recently moved to Adelaide (that's not the problem yet), and I had a large slab of red cedar that I was intending to prepare for a table top. Unfortunately, with the move and difference in climate between Sydney and Adelaide, the slab has cupped in quite severely. For teh moment I have put it on my benchtop and clamped some 2 by 4s to try to redress the damage but I don't think it's gonna do much. Would anybody have any idea about what I can do to make the slab flat again? (the slab is about 5.5 cms thick)
THanx a bunch
CHeers
Steph
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26th January 2011 02:35 PM # ADSGoogle Adsense Advertisement
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26th January 2011, 06:06 PM #2SENIOR MEMBER
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There are quite a few posts around on this topic. One way is to wet the outside surface (convex) with water while keeping the other (concave) side dry. This will pull it back a fair bit if repeated for a couple of days.
Try searching the forums.The world is a comedy to those that think, a tragedy to those that feel.
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26th January 2011, 09:07 PM #3Intermediate Member
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My dad was able to reduce a 10cm cup to about 5mm on a 30mm thick bit of pine using yowies method. Just remember to keep tighten the clamp progressively, when you wet it again. Half a day each time for as long as it takes. It will always spring back a little bit, like metal when you bend it so to get it flat you will need to make it flex the other way slightly.
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26th January 2011, 09:17 PM #4
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26th January 2011, 09:36 PM #5GOLD MEMBER
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Go with Alex . How about a picture to show the grain if possible .
I've just become an optimist . Iv'e made a 25 year plan -oopps I've had a few birthdays - better make that a 20 year plan
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27th January 2011, 02:05 PM #6SENIOR MEMBER
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My bad. Sorry.
The world is a comedy to those that think, a tragedy to those that feel.
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27th January 2011, 02:59 PM #7
Thank you for the answers. I heard about putting water but I thought it wouldn't work on such a thick slab. Now once (if it works) it is back to flat I guess I should screw a couple of battens underneath the slab so it doesn't move too much when it is turned into a table, am I right? If yes, shouldn't the screws be able to move a bit along the battens to compensate for the natural wood expansion?
Cheers
STeph
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27th January 2011, 03:32 PM #8GOLD MEMBER
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I saw a recent post here somewhere(can't find it now) where the author routed a groove in the underside of the slab, across the grain , and glued a strip of wood into the groove . I thiught that was neat as it was hidden . Perhaps someone who suffers less from KRAFT disease than me might recall the post
I've just become an optimist . Iv'e made a 25 year plan -oopps I've had a few birthdays - better make that a 20 year plan
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27th January 2011, 06:27 PM #9
Steph, with a slab that thick you can make the concave side quite wet, and leave it for several days. The aim is for the moisture to even out through the board. You may need to progressively tighten the clamps rather than flatten it in one go.
Being cedar, I suspect that it probably cupped because the board was lying flat on a bench or something, and one side was exposed to humidity changes. Cedar is otherwise usually stable, and doesn't cup much, but like all timbers, it expands radially and circumferentially, so you will need to allow for this when you attach it to the top. You can do this using buttons or slotted screw holes (as you suggested), or a sliding dovetail support routed in the underside of the tabletop, depending on the table design. A search on these forums will find plenty of posts.
Would like to see some pics when you get a chance.
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27th January 2011, 09:36 PM #10Member
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27th January 2011, 10:01 PM #11
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27th January 2011, 10:02 PM #12GOLD MEMBER
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28th January 2011, 08:25 AM #13
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28th January 2011, 09:11 AM #14Jim
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Couldn't resist looking. you learn something new all the time even if you wished you didn't.
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28th January 2011, 06:35 PM #15Senior Member
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Cupping slab of cedar
Hi Stef 1611
There is reputedly merit in the wetting one side and re-drying technique reported by some respondents to the post.
Before following that track I suggest the following. I suspect your problem is that you have placed the slab in some position where differential drying could occur more on one face than the other and that has caused the cupping. Just reverse the orientation of the slab in the same position where you had it before and wait for results. You may get a pleasant surprise.
I suggest you don't adopt any form of rigid cross banded approach to trying to limit wood movement. We have known for 2000 years that it doesn't work and we don't all have to learn by making our own mistakes
Cheers Old Pete
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