Cupping suggestions!!

[jimmybigfoot]

Hi guys, anyone know how I can get a 5mm cup out of this 30mm thick table top which is 600mm long. It's in kiln dried pine and has just decided to give me a headache. I have biscuited 6 pieces of 100mm wide and we're all jointed perfectly.

I've doweled the legs on.
Thanks
Jim

 

[andersonec]

How is it fixed to the leg frame? a picture from underneath would help.

Andy

 

[RobinBHM]

You could turn it upside down on a pair of trestles, then place an oil filled electric rad in between the trestles. Turn the heater on a low setting so it warms up the convex side. It could take a few days, but it will flatten it. There is of course no guarantee that it will return to totally flat as the top is made of wide laminations and they may react equally, so it could end up slightly uneven. Ive been able to flatten significant cupping in 40mm thick worktops with this method.

 

[undergroundhunter]

Put a decent breadboard end on it.

Matt

 

[Random Orbital Bob]

Assuming its not already fixed to the legs, get 2 or better 3 thick cowells and clamp then across the bow, flattening it. Leave them in place, preferably in the environment it will end up in for as long as you can (6 weeks would be good if practical). Once out of the cowells, fix it to the apron and legs quickly.

 

[n0legs]

Once out of the cowells, fix it to the apron and legs quickly.

What are cowells??
Do you mean cauls ROB :?

 

[Random Orbital Bob]

That's the pup

 

[Monkey Mark]

Once out of the cowells, fix it to the apron and legs quickly.

What are cowells??
Do you mean cauls ROB :?

I preferred it when it was cowells :mrgreen:

 

[n0legs]

I preferred it when it was cowells :mrgreen:

That could be whole topic on it's own

 

[jimmybigfoot]

Thanks for the help guys, I'm going to try clamping it down to a work bench and putting a skirt under and maybe a breadboard end

 

[Racers]

You could rip it along the glue lines and re-joint the edges as a last resort.

Pete

 

[custard]

You could rip it along the glue lines and re-joint the edges as a last resort.

Pete

Personally that would be my first resort. The wood's telling you that it doesn't want to lay flat, and breadboard ends and heavy clamping won't make it change it's mind.

I'd rip the joints apart, let it dry and settle some more, then re-joint in a way that keeps the wood happy and content.

 

[Myfordman]

+1 for rip and rejoin. Make sure that if you are going to add any finish that this is applied equally to top and bottom

 

[dickm]

Can't really add to the suggested answers, but like the look of the background tractor . What is it?

 

[blackrodd]

You could rip it along the glue lines and re-joint the edges as a last resort.

Pete

Personally that would be my first resort. The wood's telling you that it doesn't want to lay flat, and breadboard ends and heavy clamping won't make it change it's mind.

I'd rip the joints apart, let it dry and settle some more, then re-joint in a way that keeps the wood happy and content.

+1 More for the above, for the long term solution.
Rodders

 

[jimmybigfoot]

It's a Chinese 25horse dong feng.

 

[Sheffield Tony]

I'm going to dare to differ with the suggestion of ripping it and re-jointing. IMHO, if there is nothing to hold a piece of wood flat, it will not stay so. With the possible exception of very nicely quartersawn timber, which this is not.

Wood expands/contracts with humidity about twice as much tangentially to the annular rings as radially. So whatever you do, it will only want to be flat of its own accord at one humidity level.

The fault is the design, you need the top to be held flat across the grain by a rail/cleat/apron whatever you call it between each pair of legs, or breadboard ends. And it needs to have slotted screws to hold the top on, or oversized mortices in breadboard ends to allow it to expand/contract.

Edited to add: you might find this a good read:

https://www.finewoodworking.com/media/TabletopsFlat.pdf

 

[blackrodd]

An excellent link you've posted Sheffield Tony, Explains it all, Well worth a bookmark!
Thanks Rodders