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 Failure: Gradual Strength after Failure: Superior Rigidity: Very Stiff
Round Edged Floating Tenon
Strength: Excellent Rate of Failure: Gradual Strength after Failure: 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.
I believe that a traditional mortise and tenon is slightly stronger. However, if I was building this door, I would not hesitate to use floating tenons. Although in this case, I would use 2, 3/8"x 5"wide x 6" deep tenons on each joint. I would also epoxy them. Do NOT forget to cut a glue relief slot or two in each of the tenons. DAMHIKT!
Dave
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I have built numerous doors, all using floating tenons. I just delivered a pair of 30" doors with tempered glass similar to what you've described. Mine were made from Vertical Grain Doug Fir. My doors were
1 1/2" thick and I used 1/2" tenon stock.
I have never had a problem with doors sagging or racking, but the oldest door is only 6 years old, so I guess it's possible that a problem could develop in the future. If you have any qualms about the strength, I would suggest that you drill for a metal screw in each tenon at the 4 corners, and plug the holes with face grain doug fir plugs. However inelegant, the screws add a lot of strength. Also, make sure your tenon stock really matches with width of your mortises without any additional space in the mortises. The tenons can't really rack if there isn't a void to rack into . . .
Thanks Rick, how deep did your tenons go into the stock? and what glue did you use? yes i plan on "pinning" the tenons (character) BTW to router out the inset for the glass I was just going to use a rabbiting bit and clean up the corners. thanks
No competition for strength and durability on a door of that width definately wedged 'traditional' mortice and tenon joints. Coming from the old school i think of loose tenons as overgrowm dowel joints relying totally on adhesive to retain strength whereas a well constructed wedged mortitice and tennon joint will actually hold itself without relying on the adhesive
I plan to do most of my joints with Floating Tenons and am waiting (New Year's is the promised date) for Festool's new Domino F/T cutting machine. Hand-held, much like a biscuit jointer. Already reased in Europe and completely sold out.
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