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How to flatten a cupped tabletop

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Forum topic by festus77 posted 10-28-2010 03:27 AM 6653 views 0 times favorited 10 replies Add to Favorites Watch
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festus77

18 posts in 2527 days


10-28-2010 03:27 AM

Hi all,

I’ve got a friend who has an old 42” 5/4 thick round oak tabletop. He was going to refinish it, stripped just the top and put it in the garage to work on later. It is now cupped about 3/8”-1/2”. He’s now asked my advice about how to flatten it. I’m not exactly sure the best way to proceed. My initial thought was to plane both sides to remove high spots, but now I’m not real sure. Doing that will reduce thickness too noticeably. Is it possible to strip the other side and maybe put some weight on it to eliminate some of the cup? Any other ideas?

Thanks,
festus

-- “We have constructed a world in which the potential for high-tech catastrophe is embedded in the fabric of day-to-day life.” Malcolm Gladwell


10 replies so far

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GaryL

1094 posts in 2295 days


#1 posted 10-28-2010 03:48 AM

Try stripping the whole top and let it sit for awhile. This will allow the wood to dry evenly all the way around. It’s a crap shoot whether it will even out or not. Hopefully it will get close enough to plane flat. Which way did it cup? Concave on the top or bottom?

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

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festus77

18 posts in 2527 days


#2 posted 10-28-2010 04:06 AM

It cupped concave on top (stripped side).

-- “We have constructed a world in which the potential for high-tech catastrophe is embedded in the fabric of day-to-day life.” Malcolm Gladwell

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Howie

2656 posts in 2387 days


#3 posted 10-28-2010 04:20 AM

Like Garyl said,strip it all, then try putting it on a flat surface with a cinder block in the middle for a few days.

-- Life is good.

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GaryL

1094 posts in 2295 days


#4 posted 10-28-2010 04:30 AM

If it cupped towards the top that means the bottom still has more moisture than the top that is now open to the elements. I think if he strips the bottom he might get lucky. If possible try to put it in an enviroment with about 40-45% humidity. Perhaps a basement.The top may have been finished originally with a higher than desired moisture content and if it dries to fast it may crack.

-- Gary; Marysville, MI...Involve your children in your projects as much as possible, the return is priceless.

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DrDirt

4169 posts in 3207 days


#5 posted 10-28-2010 05:47 AM

Another thought – was this top attached to an apron with clips/cleats?

It may just be that when reattached to the base, the cleats on the bottom will help pull it flat to the frame again.

Never done it but seen the presentation from a restorer, where in order to remove the curve some will cut a relief kerf so it will relax flat and be held in place on its pedestal/frame. Mitch Kohanek at Dakota college has done this, and I saw it in some discussions at Marc Adams School last summer, however that is major surgery and easy to really mess up big time.

-- 'Political correctness is fascism pretending to be manners' ~George Carlin

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Howie

2656 posts in 2387 days


#6 posted 10-28-2010 01:31 PM

Dave: I saw Norm Abrahams pull that little trick about a week ago. Wasn’t a table top but a cupped board. Worked for him .

-- Life is good.

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Moron

5032 posts in 3358 days


#7 posted 10-28-2010 01:45 PM

what was flat, will return to flat

like so manyt have said. Strip both sides then place cupped side “up” on top of stickers (1” x 1” strips) to allow air to flow under it. Use a damp cloth, and dampen cupped side

repeat.

-- "Good artists borrow, great artists steal”…..Picasso

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doorslammer

108 posts in 3034 days


#8 posted 10-28-2010 02:31 PM

One trick that has worked faily well for me is to lay the concave side down in the yard on the grass and the convex side up in the sun. Let it sit out there for a while. The dry concave side will pull moisture from the ground while the sun will bake out the other side. Monitor it closely though, you can quickly have the same problem in the opposite direction. Once you get it resonably flat I would bring it back inside and constrain it from any other movement and let it re-acclimate.

-- Aaron in TN -http://www.amwellsfurniture.com

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aurora

228 posts in 2717 days


#9 posted 10-29-2010 12:34 AM

GaryL is right on with his moisture observation. strip both sides. moisten the side you want to grow and place it down on rags and expose the side you want to shrink side up exposed to dry air until you get is flat again.

the trick is holding it flat once you get it there !

option 1: polyurethane the whole thing, no guarantee it wont move, so this is like a bit of russian roulette.

option 2: cut two dovetails on the table bottom across the width of the table and insert dovetail cleats to hold the table flat. This is a very old method for attaching tops that I have used a number of times with good success. lets the top move and expand, yet keeps it flat and secure

see link to a big table i built using this method. http://lumberjocks.com/projects/18559

this holds the top real flat no matter what it wants to do.

good luck

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Jonnyfurniture

59 posts in 2291 days


#10 posted 10-29-2010 01:15 AM

I use doorslammers method all the time. When it’s flat again screw it down.

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