Expert: Jamie Yocono - 12/14/2006

Question
I am making a walnut dining table - nearly 4'x5'. I haven't put a finish on it yet. The other day, as I was finish sanding, I noticed that the top had cupped upward about 1/4". The table top touches the two short aprons in the center, but doesn't touch the side aprons at all.

The table has tapered legs attached to aprons. There aren't any lower stretchers. I have metal table top fasteners to attach the top to the apron.

The top was cupped a little bit initially - but not nearly so much. It was pretty flat, but not perfect. I was shocked the other day to see that it had cupped so much that it didn't touch the aprons on the long sides of the base. The table has been in the same woodshop for a year, so it has been through warm weather (w/ no AC in the shop) and cold (w/heating in the shop).

If I try to attach this table top, would I push down and try to tighten the screws so that the top will be secure. Or will it wobble since it isn't touching the side aprons?

Or should I flip the top over so that it is cupping down? Having the top flipped this way allows the top to touch nearly all points of the apron except two points in the center of the short aprons.

This was a project for a woodworking class and it is the first large table top I've made.

Thanks for any help you can provide.

Jenny  

Answer
Hi Jenny,

First off, let me say I admire you building that large of a table in a woodworking class. That's a big undertaking!

I have a couple of questions/comments about the problem you have. Did your instructor talk to you about grain alignment when gluing up that big top? I'm curious if you used wide boards, or ripped them down to narrower strips, which is the right way to do it.

The correct way to glue up a wide top is to lay it out with boards that are roughly 3-6" wide. Because I'm sort of neurotic about my wood grain, I almost always try to make it symmetrical. So if I have a 16" wide top, I'll use 4 boards that are 4" wide. Or a 20" wide would have 5 boards that are 4" wide. And so on. Actually, I like an odd number of boards in a top, so I prefer to use 3 boards or 5 boards or 7, and so on. What that does is this: if the math doesn't work out equally, then that center board can be a little narrower than the rest, to compensate. I hope that made sense!

Anyway, to get back to your top- the two questions would be- how wide were the boards you used, and next- what was the annual ring alignment? If you look at the end of a board (a wide board is easiest to use as an example) you'll see the annual rings. The annual rings will tell you how the board will cup. It will generally cup the opposite direction that the rings are running. So the correct way to glue a top is with one board's rings curling up, and the next down, and the next up, and so on. You alternate the rings to reduce cupping. Which is why I suspect you have that massive amount of cupping. I feel like you probably laid the table top up for aesthetics, not looking at the rings, and you're seeing what can happen!

Sometimes, people call my studio and say they have a 24" wide board of wood that they want made into a piece of furniture. Even though it's tempting to use that one wide piece for a furniture component, I know in my heart that the proper way to use that wide board is to rip it into narrower strips, and with every other rip, flip it over to change the annual ring orientation. It's the only way to keep a wide board from cupping.

So- how do we fix your table top? There are a few ways. I don't recommend using it the way it is. Even if you clamped it flat and used those metal table top fasteners, there's a chance the top will still pull away from the aprons. I don't recommend flipping it over, either, as the crown in the top of it might actually cause your dishes to teeter. Yikes!

I know you probably don't want to hear this, but I suggest ripping it down into a minimum of 3 pieces. A 4' wide top could be ripped into 3- 16" wide strips. Then- after putting a fresh, 90 degree edge on each board, reglue them, flipping the center board. That way, the two outside boards remain the same, but the center board, which had most of the cup, will now be a less visible crown. Cutting the top down will release some of that internal tension in the boards that is causing that massive cup.

Another thought- I recently built 2 large tables, one 4' wide, and the other was 6' wide. When I calculated the amount of expansion and contraction these tops would undergo with seasonal atmospheric changes, I decided to make them split tops. My 4' top is actually comprised of 2 pieces, each 2' wide. They are connected by this piece of hardware - use this link to see what I mean:

http://www.rockler.com/product.cfm?page=6000

This piece mounts on the underside of the table and keeps the two halves perfectly aligned and flat. I think on both of the tables, I used 3 of these per table. They work great.

I didn't look up in my reference books, but I suspect that walnut top of yours could shrink or swell with the seasons as much as a 1/2" or more along it's width. (It's not going to move much, end to end.) Make sure you give it some room to move when you attach the top with those metal table top clips.

OK, good luck, I hope this helps. Please feel free to write back if you have any further questions after reading this. And if this answer was helpful... please take a minute and rate my service. Thanks!

Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV
www.wooditis.com