Table Top Expansion Question

[John B]

I don't know whether I can explain this or not, but SWMBO wants a chest she showed me in a furniture store. The top was constructed with six boards running lengthways dadoed into boards on the ends running crossways. Sort of like this: |==|

It seems to me that as the lengthways boards expand and contract, they will pretty rapidly crack that dado joint. Any thoughts?

[bradnh]

John,

What you are describing is commonly known as "breadboard ends." Your instinct re the expansion of the lengthwise boards is right on. In fact, breadboard end joints are specifically there to deal with that expansion. Usually the tenons on the end of the lengthwise boards, which fit into the dados on the cross-wise end boards, are not glued, or, they may be glued only at the center board,or, they may be pegged to the center board (only)without glue. Any of these would allow for the free expansion and contraction of the lengthwise boards across their width, while these boards are still "captured" by the breadboard ends. The breadboard ends also hide the endgrain of the lengthwise boards. It's an elegant solution which has stood the test of time.

Brad

John B wrote:

[RonB]

I would add that the second purpose of the breadboard ends is to help keep the tabletop from warping - they add some rigidity at each end. The pegs, screws, bolts or whatever is used in the glueless outer areas use slotted holes or similar device to allow for some movement of the main top.

After you build one of these, it will provide a pretty good lesson on how wood expands and contracts in width, but not length. You can always walk past it, run your fingers across the end of the joint and feel the effects of nature. On one I built it is usually: Dryer winter - breadboard proud, Humid summer - tabletop proud even in air conditioned environment.

[Brikp]

See some the discussion that started on a post I made about Breadboard ends. I ended up doing this with a sliding dovetail joint instead of T&G. It came out very nice if I can say so myself.

I cut a dovetail finger on the top and a dovetail slot on the breadboard end. I used the router table. I made two passes for making the slot, 1 time facing each way. That ensured it was perfectly centered. I then moved the fence and cut the finger. I adjusted the fence a bit closer for each pass on each side so I could creep up on the size of the finger I needed. It was really pretty easy. I made the fit pretty tight. I used a pin from underneath to lock it centered. (Even though I cant imagine it moving very much on my small top.

Good luck.

[Ba r r y]

DAGS "breadboard end"

Web:

Newsgroups"

In short, the ends are only attached at the center, which lets the center boards move. Unless, of course, the "boards" are actually plywood.

Barry