Through tenon wood expansion

[Phil Mueller]

I’m building a mission style table for a friend similar to this design:

435938

Regarding the shelf’s through tenon. Assuming the through tenon is “tight” in the mortise, how do you allow for wood expansion of the shelf? Or do you?

I’m working with very old reclaimed knotty pine interior paneling. The shelf will be approximately 7” wide and just shy of 3/4” thick. I’m thinking around a 1/2” tenon.

Appreciate any insight from those of you who have experience with this sort of joinery.

[roger wiegand]

I don't know for sure, as I haven't done the experiment. In winter I leave a small gap for summertime expansion, in summer I make them reasonably tight. The wood will certainly move, it may be that it would simply compress if made tight when at its driest and then have a gap when winter comes again after it has cycled. In any event I pin them in the center and leave them free to float. The tables I've made have been in the Greene and Greene style and with the rounded over members the gap is not noticeable.

[Phil Mueller]

Thank you Roger. I think a small gap is probably the only way to go.

[Andrew Hughes]

Im thinking it really shouldn’t matter much. If the piece is made from rift sawn or quarter sawn even better.
But I’ve never made that piece it looks like a nice design.
Good Luck

[Patrick Walsh]

I agree, nice design.

I might have to make one, I have a perfect spot. And a bungalow...

I wouldn’t worry one bit about it.

[Phil Mueller]

Thank you Andrew and Patrick. I guess since it’s the highest humidity right now, I’ll go snug.

[Robert Hazelwood]

You could also make the through portion of the tenon narrower, and let the rest of it be blind. Then you can allow some expansion gaps on either side of the blind tenon.

[David Sochar]

I think it is nothing to worry about too much. At 7" wide, there cannot be much movement. Take a look at the Shrinkulator to find out for sure:

Shrinkulator (http://www.woodbin.com/calcs/shrinkulator/#:~:text=The%20Shrinkulator%20helps%20you%20estima te,saturation%20point%20(about%2028%25).)

Follow the link above to do a run thru of your conditions.

I did a calculation and guessed at some parameters, but a change from 10% to 7% will only change the dimension by 1/32". That is a zero as far as construction is concerned.

It is not unusual for us (doormakers) to have a 10" wide Rift W Oak bottom rail glued into a stile the entire 10". This breaks "the rules", but in practice it is exceedingly rare to have a problem. And those rail/stile joints are out in the weather, with 110 degree temp swings and humidity to match. I have doors that are out there for 30 years that still look fine.

[Phil Mueller]

Thank you Robert and David. Interesting idea, David...may have to do that. Appreciate the experience, Robert, and link. You (and others above) are right...not much movement going to happen.

And to all, truth be told, this is my first through tenon...so there’s a good chance there may be a bit of a gap...planned or not :o

[Rob Luter]

I wouldn't worry too much. I built this 9 years ago. Construction is similar to what you propose. The shelf is QS, so it won't move much width wise, but it will move. Movement will apply force to the end grain like a tusk tenon key. It was snug when I made it and it's still snug today.


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[Bill Dufour]

I don't know for sure, as I haven't done the experiment. In winter I leave a small gap for summertime expansion, in summer I make them reasonably tight. The wood will certainly move, it may be that it would simply compress if made tight when at its driest and then have a gap when winter comes again after it has cycled. In any event I pin them in the center and leave them free to float. The tables I've made have been in the Greene and Greene style and with the rounded over members the gap is not noticeable.

reverse that in my climate.
Bil lD

[Phil Mueller]

Bill, I grew up in Fresno, so I understand hot, dry summers.