Thread: Severe cupping

Originally Posted by AlexS

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

And suddenly, following that link was worthwhile after all...

Originally Posted by old pete

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

Thanx Pete,

I think most of the cupping occured on the move from Sydney to Adelaide and I don't think I can put it back in the position it was. I haven't had time to try the water but I will this weekend and see what happens. I am a bit concerned though, I wonder what will prevent further cupping after the slab is mounted as a table in the future. May be I should add a breadboard on each end of the slab, should help preventing cupping no?
Gotta check this Kraft thing now...lol
Cheers
Steph

I wonder if water on the concave side helps for the Kraft desease

Originally Posted by stef1611

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

Hi Again Step1611,

If the slab is correctly dried and does not exhibit a big core to case moisture gradient it should not move in service and should not require restraining joinery. I'd suggest you test the moisture content at the surface and in the core with a good quality resistance moisture meter ( I wouldn't use a capacitance meter).

If the meter readings are OK then saw the slab in half lengthwise, flatten the faces on the buzzer, pass the two halves through the thicknesser, straighten and square the edges on the buzzer and join with biscuits or Dominos set at about 300mm intervals. Set the first joiner about 50mm back from the ends. For a slab that thick I'd use two rows of Dominos or biscuits.

A table top of 50 or 55m thickness is pretty thick by visual amenity standards IMO and IME particularly if it is natural edge and can look a bit heavy and clunky unless you are fortunate enough to live in a baronial castle that will show it off nicely so don't worry about losing a fair bit of thickness in getting the slab re-constituted back to flat. I never go over 30mm perhaps 32mm.

Good flattening Old Pete

Originally Posted by old pete

Hi Again Step1611,

If the slab is correctly dried and does not exhibit a big core to case moisture gradient it should not move in service and should not require restraining joinery. I'd suggest you test the moisture content at the surface and in the core with a good quality resistance moisture meter ( I wouldn't use a capacitance meter).

If the meter readings are OK then saw the slab in half lengthwise, flatten the faces on the buzzer, pass the two halves through the thicknesser, straighten and square the edges on the buzzer and join with biscuits or Dominos set at about 300mm intervals. Set the first joiner about 50mm back from the ends. For a slab that thick I'd use two rows of Dominos or biscuits.

A table top of 50 or 55m thickness is pretty thick by visual amenity standards IMO and IME particularly if it is natural edge and can look a bit heavy and clunky unless you are fortunate enough to live in a baronial castle that will show it off nicely so don't worry about losing a fair bit of thickness in getting the slab re-constituted back to flat. I never go over 30mm perhaps 32mm.

Good flattening Old Pete

THanx Pete for the detailed instructions,

Thing is the slab is a bit irregular in the sense that once side goes into forming a nice almost circular shape, starting from the other side that is quite straight, and since the grain looks beautiful as is, I was thinking of just putting the whole slab onto a table base and leave it like that as a slab. I don't live in a manor but I have a very big study because of my job so I'll have plenty of space in the room if I leave it like that. I'll test the moisture content and see if I can get away with doing that without having to worry about further cupping. I'll put a pic as soon as I can escape in the shed.
Cheers