Breadboard Ends Oak Cutting Board
#25
Interesting.  Thanks all.

For reference.  The tenons are 2" wide, and the gap between them is 2".  Mine, as well as Paul's example.
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#26
(08-24-2016, 02:25 PM)Paul-in-Plymouth Wrote: [T]he mismatch from seasonal expansion and contraction is confined to a central “rectangle” of sorts defined roughly by the 4 tenons and 4 pins that attach the ends to the main body.  

If the constraining rectangle is small, the stresses may be small enough to be tolerated.  If not, then the constrained piece may crack.

Outside that constrained area, the “wings” are free to expand and contract unconstrained by hard attachment to the grooves they ride in.  In that case, I don’t see how the size of the wings, absolute or relative, matters at all.

That said, I do not understand why you say the ratio is important.

This all makes sense to me.
John: Struggling along with a "piece of junk" table saw
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#27
"For reference.  The tenons are 2" wide, and the gap between them is 2".  Mine, as well as Paul's example."

There are several things going on with this wood project--as I would consider. Just throwing them out:

1. The go-by is a cutting board(?) by Paul Sellers. Thanks to Derek Cohen posting an image, we can assess it also. Sellers board is vertical grain Oak. Radial movement is generally half of tangential (flat sawn). 

2. The critical dimension of wood movement is 6-inches, at the outer edges of the through tenons. 

3. OP's Red Oak board is tangential grain with movement approximately double that of quartersawn. Oak ranges from 4.5 percent to 5.6 percent movement radially. Tangential movement in Red Oak is roughly  0.1" in 6-inches, or; 0.05 inches at each outer tenon. Not a lot. And, most constrained joints are maximized at 3.5 to 4 inches. So, the Red Oak board could theoretically be happy--in my mind--on the counter.

4. However, this wood does not conform to standard seasonal movement regimens. It will be periodically soaked in fluids, water mostly, in the summer, fall, winter, and spring. Expansion will be greater than one-tenth inch. But in favor of moisture, cell compression will actively keep the tenons in place and the glue joint will probably separate at some point. The board will still function, but be somewhat looser.

5. Chop, chop away!!

Thanks for being a party animal.
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#28
The purpose of a bread board end is to maintain a flat surface while permitting seasonal movement in a panel (which may form a table top, a lid or a cutting board). 

The design calls for a central mortice and tenon that is fixed, and outer mortice and tenons that can move. Movement occurs across the full length both the morticed and the tenoned ends. The design calls for enabling movement from the centre outwards. Now, if there is too much area trapped in the centre, then the movement will be limited, and the likely result is the wood splitting. Consequently, one must be careful not to trap too large an area at the centre.

I apply the "one-thirds rule" for breadboards, as well as for mortice-and-tenon joints. This means that the centre third can be trapped, but the outer thirds must be free to move. In my example (the lid), only the centre tenon is drawbore pinned and glued, and all the other mortices are wider than the tenons, and clamped without glue in a pinned slot. 

What is do not like about the Sellers example is that it has through tenons. It may look pretty, but this design ensures that there can be no movement in this section of the board/end piece. That is a poor choice for an item that will get wet, or is just more open to the elements.

A good example of design is seen in this video ..

https://www.youtube.com/watch?v=oDvdfuzk6pU

Regards from Perth

Derek
Articles on furniture building, shop made tools and tool reviews at www.inthewoodshop.com
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