Removing cup from a glued up panel

[Matt Day]

I've got a glued up panel of 1" thick soft maple (6 boards, 35" wide, 90" long) that has a little bit of cup lengthwise, and I was hoping that breadboard ends would keep it straight. I haven't cut the mortise or tenon yet for the ends, but I forsee a curved tenon and a straight mortise that aren't going to match up.

I was planning on putting some steamed towels on the concave side, covering it with plastic to slow the evaporation, and hoping that it flattens out enough to install the ends. If this is a good plan, should I cover the whole top with steamed rags, and how long should it take?

Thanks

P.S. I'm sure a similar topic has been discussed, but the search engine doesn't seem to be the greatest and always returns irrelavent threads that were started recently. Anyway, sorry if this has been beaten to death.

[Jim Becker]

Be sure you are using the "Advanced Search" to refine your objectives.

If this panel is indeed going to have breadboard ends and be fastened down onto some kind of structure, it will likely flatten out during those processes. Make sure you clamp that panel down tight on a flat surface before you mill the ends...I'm assuming you will be milling your tenons with a router due to this situation.

[Jamie Buxton]

The effect of steam is rather uncontrolled, and if you used ordinary PVA it might attack the joints between the boards. You might consider clamping boards across the table to flatten it while you cut the tenons. Stand the clamping boards on edge; they're much stiffer that way than on the flat.

After you put the breadboard ends on, the table top is still likely to be cupped. The table aprons will do more to remove the cup. If you're lucky, the table top is concave down, and one screw in the middle of the apron will pull it right down.

[Matt Day]

Thanks for the quick advice!

I was planning on clamping it down flat w/ boards before routing the tenon. I appreciate the reassurance though!

The highest part of the cup, luckily, will be up when it's finished. And it's a trestle table that will have four battens to secure the trestles, which should help keep it flat.

I'll stay away from the steaming techique too.

Thanks, and I should find out if it works tomorrow!

[Jim Becker]

Matt, just be sure that the method you use to fasten the table top to the trestle allows the panel to "move" seasonally...

[Matt Day]

Will do Jim. Both the breadboard ends and the battens will have elongated holes on all but the middle screw to allow for movement.