"mcgyver" wrote in message
Building an old growth fir front door. 2 Rails and 2 stiles(42"x80") which
will have a 30"x60" double pane of glass in the middle. I'm going back
and
forth on traditional M&T joints or a floating tenon joint done with my
plunge router (I've done lots of these joints before) I'm concerned about
the strength and particularly whether this joint will support the racking
forces once the door is hung.

I'm thinking 1/2" think tenons by 5" wide and
2 1/2" deep mortices. Any suggestions on the sizes needed to keep this
together?

Pretty hard to say without knowing the thickness and width.

With regard to strength, here's how FWW tested the top two in the Mortise
and Tenon test back in 3/01:

Traditional M & T

Strength: Superior
Rate of Failu Gradual
Strength after Failu Superior
Rigidity: Very Stiff

Round Edged Floating Tenon

Strength: Excellent
Rate of Failu Gradual
Strength after Failu Excellent
Rigidity: Stiff

Although he stated that the test subjected the joints to more severe forces
than they were ever likely to encounter, the tester concluded that he would
use traditional M & T when faced with the need for a super strong joint that
must not deflect.

Sounds like your door might fall in that category. But the question I would
ask myself is whether the proposed width of your tenons might make
dimensional instability of the wood a factor that would negate the above
results, and whether you would want to haunch them?

On the lock rail, you might want to consider a doubled mortise and tenon,
with the gap in the tenon usually being no more than 1/3rd the width of the
rail, and with a haunch in the gap.

There are books written about this ... might want to do some more research.

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Last update: 7/30/06