In the current issue of WOOD magazine, they give plans for a nightstand. The side and back aprons are 8.75" deep with 8.25" tenons. The tenons are cross-grain glued into the legs!
Has someone repealed the laws of wood movement?
I think I'll write them and ask :-).
If it's in a conditioned/humidified house it may not be too bad. However, build it in arizona and take it to florida and you'd probably be asking for trouble.
Chris
I had not seen this yet (are you referring to Nov or Dec 08?), but if there are 8.25" tenons just apply glue to the top 3-4 " of the tenon to allow for movement.
I know that, but apparently they don't. In addition they left no slop in the mortise to allow for such expansion.
If the aprons were glued only at the top, there wouldn't be sufficient support for the legs. What I would do is separate the single large tenon into three smaller ones (2"-3"-2") with space between them and at the ends of the mortise. Then I'd glue only the top and bottom 2" tenons and let the middle 3" one float.
I'm referring to the Nov/Dec issue as it's only published every other month.
Larry Blanchard wrote: ...
... Not seen what they're actually doing, either, but seems like that would still be an issue as the middle one isn't the one that needs to move. Seems like two fixed tenons on either side of a 8" wide piece even individually narrow are still likely to need some way to move relative to each other or will eventually fail the joint.
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I don't recall a mention of the parts thickness, but a time honored general 'rule of thumb' is that a tenon should be no wider than 5 times it's thickness before going to another tenon.
This is pretty standard stuff in door making, which makes liberal use of double tenons on some pretty wide rails, with either a space or haunch in the middle, each component being no more than 1/3rd the width of the rail.
Depending upon thickness, on a wide table apron I'd probably forego a haunch in the middle, but use a "haunched mortise and tenon" for the top tenon of double tenons, so it doesn't break through the leg endgrain.
Following either above, it is accepted practice to glue both the top and bottom tenons. I've never had trouble doing that, but nothing I've built has been around longer than 45 years either.
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