Expert: Jamie Yocono - 4/27/2005

Question
I made a 5'X 4'dinning room table just about a year ago.  The table can be expanded with one 18" leaf. Within a few months the 5/4" oak top developed several splits on half and warped badly at the other end.  I used boards with widths ranging from 5 to 6.5" that were edge glued and joined with #10 plates every 6".  The apron was 1X3 oak pocket screwed and glued to the top that was wrapped with an oak chair rail molding.  None of the mechanical fastenings failed (the splits only took place in the middle of boards. The warping was so severe that it actually split both layers of apron at about the middle of it's width as the pocket screws & glue held the upper half of the apron table top.)  

I took great care when edge gluing & biscuits to keep the top surface as flush as possible.  This kept the sanding to a minimum. (Only 5 or 6 passes through a large drum sander were required)  The piece was stained and finished with 5 coats of poly.  The first coat of poly was cut 50% with Turpentine and I made sure the ends were sealed well.

This table is placed in a space that has radiant floor heating, and is subject to several hours of morning sun through a sliding glass door. (The end with the splits gets the most sun)

I've purchased lots of wood from this specialty wood supplier and never had any problems with any of their stuff.  Obviously the oak was not as dry as it should have been. I don't have a moisture meter and can't justify spending money for one.  I need to make another top but obviously I would like to have different results.  The conditions of the space (floor heat & sun) can't be changed.  If I used smaller width boards could I avoid the problems?  Any other suggestions?

Thanks.


Answer
Hi Stew,

Sorry to hear about your table top dilemma. That sounds awful and I think you are definitely on the right track about moisture being the problem. It sounds to me like a few things are going on, and I'll try to discuss them here.

First and most obvious- the top is adapting to it's environment. It sounds like it's shrinking somewhat, most likely from being indoors and on that radiant heated floor, and in the sun. On a top that big, it can shrink/swell with seasonal changes as much as 1/4" per foot of the width. So a 4' wide top can actually be 1" bigger when it's humid, or 1" smaller when it's hot and dry, which (I think) is occurring.

One of the problems is how the top is fastened to the aprons. A table top needs to float so that the movement will not affect any of the other parts of the table. You mentioned that you screwed and glued it. THAT is a major problem. How do you float it? Many ways, but the simplest way is to buy metal table top clips. KV makes a decent clip, try cutting and pasting this link into your browser and you'll see one that WoodCraft sells.

http://www.woodcraft.com/family.aspx?DeptID=2225&FamilyID=1036

You can also make wooden clips that are quite nice. When I am making a smaller table, I make wooden ones, but with a big table, it's much easier to go with the metal ones. Look in Tage Frid's third book on Furniture making. I think he calls them cleats, but it's the same thing. He goes into some detail about them, so it will show you how to make them, if you so choose. Grain orientation is important, so pay attention to that.

The clip rides in a small groove about 3/8" down from the top of the apron. It's on the inside of the apron, so it doesn't show, and allows the top to move somewhat when it needs to. I usually machine the groove in the apron on my tablesaw, it's just the kerf of the blade. Make a test cut on scrap first to make sure you have it in the right place. Ina pinch, you can add a groove to an apron with a biscuit (slot) cutter.

So- those clips will allow your top to float and alleviate some of the problems. But I think that if you are going to make a new top, you should acclimate the wood by letting it sit in the room for a while. I would suggest a month or so. This practice is fairly common. Ask anyone who has ever installed wood flooring- they usually let the flooring material sit in the room where it is to be installed for a while, acclimating to the room's moisture level. So putting your raw lumber in there and letting it get used to that radiant floor will help a great deal.

Last thing- you mentioned the finish you applied, but you didn't mention if you applied it to both sides of the top. Wood has to be treated equally on both sides, or it will experience some of the problems you mentioned. So if you applied 5 coats to the top, you HAVE to do the same to the bottom. If you don't do that, moisture will leave (or enter) the wood differently on both surfaces, and moisture problems can occur.

Smaller widths of wood may help, but really- the most important thing is to let that top float and allow it to move somewhat. If you finish both sides of the top equally and float it, you shouldn't have too many problems.

On a related note, I recently made a similar sized table for a client. This table was 4' wide by nearly 6 feet long. I decided to make the top in 2 parts, both 24" wide and 6' long. Yes, there is a small seam down the length of the table. But it reduces movement, and I connected the two halves with a bracket (that Rockler sells) that keeps the two pieces tightly together. I just figured that 2 small tops will experience less movement than one big one. I built a 6' square table a few years ago, and it was a nightmare thinking about all that wood moving.

Good luck, I hope this helps. Feel free to write back with any other questions you might have after reading this.

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