Mortise and Tenon

[Smoothjazz077]

I haven't used the mortise and tenon joint in my woodworking until a project I am currently working on. I am doing the joinery by hand, and just finished chopping out the mortise. Is there a guideline on how deep a mortise should be for the tenon? The project I am working on will have a high load weight requirement. My mortise is 1" in depth, and is 3" in length. Is 1" deep enough?

Thanks
Scott

[Guest]

Not enough info for an answer to your question. What are you building? How big are the components you are joining? What is your "high load weight"?
I don't know if there is a formula for the size of mortises and tenons, there probably is since there seems to be a formula for just about everything. In general, I think it depends on the size and requirements of your project. A 1" X 3" X 1/4" mortise and tenon might be fine for joining a 1 X 6 to a 2 X 4 to support a 200 lb. load, but not so great for joining a 4" X 12" rail to a 6 X 6 style to support a ton. You can probably rely on your gut. If it looks strong enough, it probably is.

My $.02.

Hank

[Smoothjazz077]

Building tools stands that will be supporting a 80lb bench top tool.

[Admiral]

I generally make the mortise depth around 1/3rd of the width of the piece being mortised, you could go deeper, actually through it; and the thickness of the tenon 1/3rd the thickness of the piece being tenoned. I don't have any source for this except for a crusty old guy named Gus (he's since passed) who told me that 30 years ago. Works for me, have never had a joint fail.

[Guest]

I think a 3" long X 1" deep mortise and tenon would be plenty for a machine table to suppore an 80 lb machine. Size the tonon 1/3 to 1/2 the thickness of the rail. Remember, the shoulders of the rail are just as important as the tenon. They keep the joint from racking; so don't make them too delicate, and make sure they are flush with the style. You might want to pin the joint too. Draw bore is nice, but probably not necessary. Just glue, clamp the joint tight and then drill and pin while still clamped for a little added security.

[MichaelMouse]

Probably are a bunch of rules - by any number of fools. In your case, the load will be borne on the endgrain of the legs - almost always the truth - so the tenons are there to prevent rail racking. It's the shoulder that counts most in those constructions, with the tenon long enough to contain a pin to draw bore it and keep the shoulder in firm contact. In hard wood, probably ~3/4" with the draw midway or favoring the entry.

Fox wedged tenon could be shorter.