Thread: Need some help here plz.

I forgot to mention alternating top and bottom with the cross clamps. That helps to even out the pressure and you can use the pipes to force the boards flat and square.

Oh dear. I've done it myself once and the problem is that the glue join is much thinner in the cup than it is on the bottom, presuming the cupped side is your top face. Did you use biscuits or a tongue and whip join between the boards? If not you might find the boards separate soon after you've fixed it to the frame, because the unequal glue regime can't cope with the natural expansion and contraction of the wood. If you did you'll find they take a little longer to separate. Glued joins can expand and contract with the wood but only if they are even in their thickness and pressure at the time of application. If not they'll expand quickly at the thin high pressure side and very slowly at the thick low pressure side, unequal expansion equals spilt join starting at the top first.
In this case you have to replace the join with an additional one or break the top down and start again.
One hidden remedy to minimise the splitting is to cut with your router, a series of 15mm wide and 20mm deep diagonal dovetail trenches right across the underside of your top in a large cross hatch pattern. Then slot in dovetailed whips that fit snugly but not too snugly as you won't be able to get glue in them. One direction is all long ones which you screw in place at the centre of each board and the other direction is made up of short whips that run between the long ones and also screwed in place at the centre of each board.
What they'll do is use their resistance to shearing forces to reduce the spreading of the boards once the glue in your butt joins breaks.
Another remedy is to bolt every board down to a series of cross rails on the underside of your table using sunken coachbolts. These rails are then checked into your bench frame.
Both remedies mean you'll have to level the underside as well as the top. The break down version is to knock the joins apart, clean off the glue and resquare the sides and clamp again using the equalized pressure technique.
good luck with it and mind you, I'm a masochist!

I did use bisciuts between all the boards, so I'm hoping the problem won't be too bad. I did notice some gaps between the boards appearing today, as we were using the floor sander outside in the sun. I'm assuming the sun was changing the moisture level in the boards and causing them to contract. The gaps aren't too bad, but they are still somewhat disappointing. We got most of the cupping out with the floor sander. The whole top now feels nice and smooth.

I've given both sides a coat of poly now to prevent any further moisture changes.