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Hello all,

I recently decided to take up woodworking. And as a first project, I wanted to do an ambrosia maple table. I had the table done by a local wood shop. I figured: If I can learn sanding and finishing it in this project, that would be a good start.

I noticed, when I picked it up, that it wasn't sitting straight on the shelf and on the bed of the truck either. We got a straight edge and found out there was a cup on it. It was about a centimeter in the middle of it. Now, I should say I am very paranoid about warping wood and in my experience from guitar playing I thought, if it goes one way, it'll usually only get worse.
I talked to the guys at the shop and they said I should just lean it against a wall, concave side towards the wall and it will straighten out.

When I got it home I laid it on the floor and propped one side up, so it could do its thing. After a few days it started straightening a little, but stayed the same, so I put the legs on top, to weigh it down. That way I got it almost straight.
However, as soon as I take them off again, I gets right back to its cup again. I spoke to the owner of the shop and he told me they never had to deal with this kind of thing before. We'll have a phone call tomorrow.

My legs are trapezoids, so when I mount them, that will probably help some with the cupping.

I have attached a picture to illustrate. It's a bit hard to photograph, but I hope you get the general idea. The concave side (top) is pointing down.
My question is: Is there any hope for it? What else can I try?
Thanks for any insights!
 

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A cup warp is caused by an imbalance in moisture content from one side to the other. This can occur if the table top was laid on a flat surface where air can only get to one side. What happens is one side of the top exposed to the air absorbs moisture from the air and swells up. This causes it to crown. It the top where turned over and elevated above the surface it is on in a few days the moisture should make that side swell up and equalize. The legs should help hold the top flat when you get those on however that can create a new problem. Wood needs to expand and contract with the weather and if you screw a board on the underside with grain running in a perpendicular direction to the top, when the the top shrinks it will split. You need to elongate the mounting holes and not tighten the screws down real tight. Allow the wood to shrink when it wants to and you shouldn't have a problem.

Another thing that would help with warpage is to finish both sides of the top. If you just finish one side that allows moisture to get to the underside and cause another imbalance.
 

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What is the size of the top? Length, width, and thickness.
What type table is it? Dining, bedside, sofa, coffee, etc?
 

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Discussion Starter #4
A cup warp is caused by an imbalance in moisture content from one side to the other. This can occur if the table top was laid on a flat surface where air can only get to one side. What happens is one side of the top exposed to the air absorbs moisture from the air and swells up. This causes it to crown. It the top where turned over and elevated above the surface it is on in a few days the moisture should make that side swell up and equalize. The legs should help hold the top flat when you get those on however that can create a new problem. Wood needs to expand and contract with the weather and if you screw a board on the underside with grain running in a perpendicular direction to the top, when the the top shrinks it will split. You need to elongate the mounting holes and not tighten the screws down real tight. Allow the wood to shrink when it wants to and you shouldn't have a problem.

Another thing that would help with warpage is to finish both sides of the top. If you just finish one side that allows moisture to get to the underside and cause another imbalance.
Thank you for your insight!
That actually makes a lot of sense. They stored the tabletop on the shelf in a warehouse with a big open gate. And it was humid in the week before I picked it up. I think, that another issue was that they closed the holes on the top side with epoxy resin and not the bottom side.

What is the size of the top? Length, width, and thickness.
What type table is it? Dining, bedside, sofa, coffee, etc?
Sorry, I didn't include all the info. It's a 260 x 120 x 4.2 cm table
It's supposed to be a dining room table.
 
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