glue area question

[Bill Carey]

If I have a 9" x 1/2" tenon glued in a well fit mortise, does that joint have the same strength as a 3" x 1 1/2" tenon glued similarly? They both have 9 sq inches of glued surface. Assume for the moment that they have no unusual forces acting on them - simply a pull apart force. Seems to me they should, but I'm hoping someone of the tech knowledge persuasion will pop in and provide some enlightenment.

[Andrew Seemann]

My first concern would be expansion and contraction across 9 inches of cross-grain glue joint.

As far as joint strength, the glue adhesion would probably be the same, but the 3" x 1 1/2" will go deeper into the other piece of wood and should be stronger.

[Jim Dwight]

I think they would be about the same. It's the same type of grain in both cases so the glue joint should be the same. But I would worry about a long shallow joint. I did one about 6 inches long on a crib but the tenon was plywood so it should not move nearly as much.

[Ron Citerone]

I think they would be about the same. It's the same type of grain in both cases so the glue joint should be the same. But I would worry about a long shallow joint. I did one about 6 inches long on a crib but the tenon was plywood so it should not move nearly as much.

I agree with Jim.

[Ron Selzer]

If I have a 9" x 1/2" tenon glued in a well fit mortise, does that joint have the same strength as a 3" x 1 1/2" tenon glued similarly? They both have 9 sq inches of glued surface. Assume for the moment that they have no unusual forces acting on them - simply a pull apart force. Seems to me they should, but I'm hoping someone of the tech knowledge persuasion will pop in and provide some enlightenment.

I remember reading somewhere, don't remember where. that you should make it with three tenons with a space between instead of one long one. as in 2 1/4" tenon, 3/4 " space, 3" tenon, 3/4" space, 2 1/4" tenon. The comment was due to the length of one tenon and board movement, don't understand it completely and never tried that long of a tenon.
Interested in what other comments are and how it works out for you
Ron

[Bradley Gray]

9" of cross grain is gonna be stressed seasonally.

If/when the glue fails the 1 1/2" long tenon will win.

[Ron Citerone]

I remember reading somewhere, don't remember where. that you should make it with three tenons with a space between instead of one long one. as in 2 1/4" tenon, 3/4 " space, 3" tenon, 3/4" space, 2 1/4" tenon. The comment was due to the length of one tenon and board movement, don't understand it completely and never tried that long of a tenon.
Interested in what other comments are and how it works out for you
Ron

I see that alot (i.e. breaking up a long tenon) on breadboard ends in furniture drawings often. I think glen Huey does those long mortise an tenon's that way.

[Richard Coers]

There is more to joint failure than glue strength. You need to consider wood strength and direction of the load. If you place a high vertical load on one corner, you have to consider that 1/2" of wood will split off a lot easier than 1 1/2".

[Myles Moran]

I remember reading somewhere, don't remember where. that you should make it with three tenons with a space between instead of one long one. as in 2 1/4" tenon, 3/4 " space, 3" tenon, 3/4" space, 2 1/4" tenon. The comment was due to the length of one tenon and board movement, don't understand it completely and never tried that long of a tenon.
Interested in what other comments are and how it works out for you
Ron

I'm not an expert, but my understanding of that was so that the piece with the big mortise has material left in it to retain strength so it's not reliant on the tenon and glue to be a solid piece. How true that is I'm not sure, but I'll be the first to admit that I've had m&t joints that weren't as nice as I wished they were.

[Tom Bender]

[QUOTE=Ron Selzer;3066576]I remember reading somewhere, don't remember where. that you should make it with three tenons with a space between instead of one long one. as in 2 1/4" tenon, 3/4 " space, 3" tenon, 3/4" space, 2 1/4" tenon. The comment was due to the length of one tenon and board movement, don't understand it completely and never tried that long of a tenon.
Interested in what other comments are and how it works out for you
Ron[/QUOTE

Ron, I don't see where that helps. The out to out expansion is the problem.

Here's solution I used, 30 years and no problem.

444043

Ok not sure how the pic got upside down

[Bill Carey]

Thanks gents - I'll break up the loose tenon into sections to minimize the movement