Tenon size?

[Dick Sylvan]

I am building some large carriage-style doors, 4' wide, 7' tall. The upper rails and styles are 5" wide and 2-1/4" thick with the lower style being 10" wide. I will be using loose tenons and am unsure how I should size the tenons. Help please. Thanks.

[Mike Cutler]

Dick

The traditional "Rule of Thumb", as a beginning point, for sizing tenons follows the 3-3-5 rule.

The tenon is 1/3 the thickness of the mortised member. The length is 2/3 the width of the mortised member and the width of the tenon is 5 times the thickness of the tenon, not to exceed more than that without being divided. The tenon should be located no less than the thickness of the mortised member form the end. Being a loose tenon, it will need to be twice the length of a single integrated tenon.
The Japanese philosophy for the tenon is to make it as long as possible without becoming a through tenon.

In the case of what you are describing I would use a loose tenon that was 6 1/2"- 7" long, 3/4" to 1" thick and 3" wide for the top. Have at least 3 1/4" to 3 1/2" of length in the stile. For the bottom rail I would divide it equally in two and use two loose tenons the size of the one on the top. Be sure to locate the tenons at least the thickness of the stiles away from the ends of the stile so that the tenon can't act as a lever and blow out the end of the stile. I would also think about pinning the tenon when done. This sounds like it will be a pretty heavy door.

[Frank Drew]

The Japanese philosophy for the tenon is to make it as long as possible without becoming a through tenon.

Nothing against Japanese joinery, but I like a through, wedged integral tenon on a heavy door.

As Mike wisely recommends for the bottom rail, don't make one long mortise/tenon; you'd lose very little holding power by having two tenons but gain a lot of strength in the mortise (more precisely, you'd lessen the weakening of the stile.)

A disadvantage to loose tenons -- not a big deal in many applications -- is that the tenon necessarily has to be a bit less wide than an integral tenon could be.

[Mike Cutler]

Frank

The Japanese also use through M&T joints that are pegged or wedged, in addition to tusk and tenon through joints. It just didn't sound like Dick wanted an exposed end grain in the stile, but I could have misread it.

I made a door a few years back out of Brazilian Cherry that was similar in size to the carriage door Dick is building, it wasn't that thick though, and only 34" wide. I didn't use loose tenons for it, but it is traditinal M&T joinery. The bottom section was 17" wide and I think,IIRC, that I used 3 seperate mortises for it. It's held up pretty good.
I'm not familiar with a haunched loose tenon. I like the idea though.:cool:

[Cliff Rohrabacher]

I just make 'em look right. Not too big not too thick not too small not too skinny. If I need to cover a lot of space, I split therm.