Cupped worktop fixing

[wobblycogs]

Hi,

I'm currently building a router table and to make life difficult for myself I've decided to use a piece of beech worktop for the table. After delivery of the worktop I unwrapped it and stored it on the workbench for a couple of weeks to acclimatise to the workshop. What I didn't think of at the time was letting air get to the underside of the worktop so it's cupped (warped perpendicular to the grain direction) as the exposed face has dried faster, the middle is about 5mm low compared edges. By clamping the worktop to my (very sturdy) router table cabinet I can get essentially all the cupping out of it.

Do you think if I leave it clamped down flat for a week it'll give up the fight and stay flat? Clamped to the cabinet there's good air flow to the top and bottom so (fingers crossed) the moisture levels will even out. I'll also be screwing it down tight (while allowing for expansion) in the final fitting. I could also easily fit four pieces of 50x50mm angle iron across most of the depth if necessary. Kerf cutting the underside is a possibility but I'd like to try and avoid that if I can.

Any other ideas? Advice on a finish would be appreciated too, I had planned on just leaving it bare but perhaps that's not such a great idea.

Cheers :-D

 

[mbartlett99]

Well that's a shame - beech is pretty mobile so I definitely would finish on all sides. It any penetrating finish would do - you'll be dragging stuff across it so I'd just use any oil finish you have to hand. Whether the cup will come out - well you might get lucky ... maybe.

 

[thetyreman]

surely clamping it will stress the wood fibres? what about planing the top flat? 5mm isn't too bad.

 

[novocaine]

flip it and let the underside dry out too. this time put it in stick correctly.

 

[Racers]

All it needs is the moisture content to be the same on each side, put it on one side with some sticks underneath and it should return to flat.

Pete

 

[pcb1962]

When I flatten plywood I sponge water on the concave side and cover with a sheet of heavy polythene before clamping.

 

[wobblycogs]

It is flipped over now, time to get on with something else for a couple of weeks.

If I can get the cupping down to 1mm in the end I'll plane the top flat. Currently under the clamps the cupping is <0.5mm in the worst spot which I'd probably just live with.

 

[novocaine]

next time, use a compressed fibre or chipboard type worktop, then it won't move at all. not as nice looking though, obviously.

 

[wobblycogs]

Yeah, I'm kicking myself for form over function. All along I'd planned on using an old length of chipboard laminate I've got lying around and then my eyes were drawn to a cheap bit of beech "that'll look great" I thought #-o

 

[ED65]

Advice on a finish would be appreciated too, I had planned on just leaving it bare but perhaps that's not such a great idea.

Not the worst idea either. But if you want to finish it, even just because you prefer how it looks, then you should. So, what do you have as far as finish goes? Decent chance you have something suitable already.

A few thin coats of shellac or varnish would be my preference, with periodic waxing if necessary afterwards to keep the top slippy as a slippy thing.

 

[novocaine]

if it's a counter top it's most likely already treated with an oil, normally tung or boiled linseed oil. best to stick to that if it's already coated. if your sure it isn't coated then as long as it's got free air all round leave it be as ED65 says.

 

[wobblycogs]

I specifically bought a piece without finish as I didn't want any potentially sticky finish. The underside won't have completely free air but it'll certainly get some air flow.

 

[novocaine]

in that case, as ED says, it's your call, just make sure you do all sides and use wax on the top. for me I'd use a poly (or yacht vanish because I'm cheap) based varnish but that's up to you.

 

[sunnybob]

Get some melamine faced chipboard and save the beech for projects. I really like working with beech.
Beware kitchen work surface though because its rarely flat enough for a router table.

 

[ED65]

best to stick to [tung or boiled linseed oil] if it's already coated.

No need to if either had been used, they don't have any compatibility issues with shellac or varnish. BLO or tung are very commonly applied first to maximise figure and chatoyance.

 

[RobinBHM]

Get some heat on the convex side to flatten it first -a fan heater works well.