Single or Divided Mortise?

[John Finley]

I am making a bed and am ready to do the M&T joints on the footboard and rails. The footbaords and rails are 1.5" thick and 10" wide. I was planning on making one tennon, but after reading some posts, it sounds like I shouldn't make the tennon more than 4" wide. Being that I have 10" of width to work with, should I make two 3" tennons, or stick with the single 4"? I have never made a divided M&T joist before. Is it as simple as two tennons spaced apart by an inch or so? Thanks for the help.

[glenn bradley]

There's different ways of course. Side by side is common for added strength on short wide pieces. For your size I would think a couple of 3" to 4" tenons one over the other with a decent piece of material left between on the mortise side would be fine.

[John Finley]

I ended up going with two 3" wide mortises that are spaced 1.5" apart. I made a test piece and it feels plenty strong. Hopefully the wood movement won't cause me problems over time.

[Greg Hines, MD]

I ended up going with two 3" wide mortises that are spaced 1.5" apart. I made a test piece and it feels plenty strong. Hopefully the wood movement won't cause me problems over time.

By making two tenons instead of one, it will help to minimize any problems with twisting of the rail in the future. That is why many frames like that have double tenons and mortises.

Doc