Thread: Severe cupping

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.

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.

WRONG!!
Damp the CONCAVE surface, then clamp the board flat on a couple of sheets of newspaper with the concave side down, for a couple of days.

Go with Alex . How about a picture to show the grain if possible .

My bad. Sorry.

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

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

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.

Originally Posted by Peter36

Perhaps someone who suffers less from KRAFT disease than me might recall the post

I googled "Kraft disease" and I wish I hadn't... I'm really hoping you didn't mean what Urban Dictionary said that means...

Originally Posted by beeroll

I googled "Kraft disease" and I wish I hadn't... I'm really hoping you didn't mean what Urban Dictionary said that means...

I think Peter meant to say CRAFT disease, perhaps look that up?

Originally Posted by beeroll

I googled "Kraft disease" and I wish I hadn't... I'm really hoping you didn't mean what Urban Dictionary said that means...

I see what you mean Beeroll.
What I meant was CRAFT disease .

Originally Posted by Peter36

I see what you mean Beeroll.
What I meant was CRAFT disease .

Understandable mistake. We were talking about bent wood, after all.

Couldn't resist looking. you learn something new all the time even if you wished you didn't.

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