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Thread: Suicide Joint

  1. #1

    Suicide Joint

    ...No, not a roadside bar in SE OK; another kind of 'joint':

    I didn't want to sidetrack the recent M&T thread with this, but discussions of other joint types there made me think others might be interested, or perhaps just unfamiliar.

    I found this referenced as a "Fox Tail Tenon", but remembered that the author also called it a "Suicide Joint" - presumably due to the ONE and ONLY shot you get at assembly? Once it seats home, the only way it comes apart is to exceed the yield strength of the wood - - or let it rot!

    It was applied to a stand I built, and the rails provided the best and most obvious 'handles' to pick up the assembly - which I anticipated could get fairly heavy. Tenons are great at resisting shear loads (cross-grain) . However, this load from being picked up would place the leg in vertical tension, and try to pull the tenon out of the mortice in exactly the same direction it went in. ...How can this go wrong? When i saw this joint, it seemed an ideal solution: I keep the same design; no way it pulls out... and a quick/dirty SketchUp of it (hope y'all can see it) - -
    FoxtailTenon1024_1[1].jpg
    And the satisfaction of it going together is IMMENSE!! Try it. You'll like it.

  2. #2
    Join Date
    May 2015
    Location
    Morocco IN
    Posts
    1,249
    hey Malcolm. I found this joint in the George Ellis book on joinery and have been looking for a place to use out. How tedious was the layout? Did it present any problems closing the joint? And yes it would be an extremely strong joint. Like you said break it or let it rot.
    You know, the worst ain't so bad when it finally happens.
    Not half as bad as you figure it'll be before it's happened.
    - Bob Curtin

  3. #3
    Quote Originally Posted by Bill Carey View Post
    hey Malcolm. I found this joint in the George Ellis book on joinery and have been looking for a place to use out. How tedious was the layout? Did it present any problems closing the joint? And yes it would be an extremely strong joint. Like you said break it or let it rot.
    99% of layout is simple - same as any other M&T joint. The only thing really different is calculating the angle of the guide block. Basically it has to match the angle of the wedge, so a little iPhone calculator trig - using the tenon depth and 'added width' of the wedge - gives you the cut angle for the guide block. Then simply use that block to pare the mortice out to allow for the wedges.

    As for closing, you can do as many dry fits as you need - without the wedges! Once the wedges go in, forget it. If the wedge is too 'fat' at the top (in my dwg), the tenon will never seat, and the parts go in the firewood pile; too skinny, and the joint will not be expanded enough, and tho' it might not pull out, it won't be solid - sort of like a ball and socket.

    I tried one prototype that worked well, then committed to the real thing. Drove it home with a rubber mallet; then resumed breathing.

  4. #4
    Join Date
    Oct 2008
    Location
    Columbus, OH
    Posts
    2,299
    Thanks for posting that diagram Malcolm. Aptly named! I've used wedged tenons on thru mortises but never thought to use them in a closed mortise.
    Brian

    "Any intelligent fool can make things bigger or more complicated...it takes a touch of genius and a lot of courage to move in the opposite direction." - E.F. Schumacher

  5. #5
    Join Date
    Dec 2016
    Location
    South West Ontario
    Posts
    1,217
    That is where digital calipers work well to measure the bottom width of the mortice, compare that to the tenon +wedges - the gaps. I've made this with chair legs, round with one wedge in a blind mortice.
    ​You can do a lot with very little! You can do a little more with a lot!

  6. #6
    Join Date
    Jun 2019
    Location
    Evansville, IN
    Posts
    13
    This is also termed Jigoku-kusabi or Jigoku-hozo, I haven't been able to find if these terms are synonymous or referencing slightly different joints. It's depicted in Wolfram Graubner's "Encyclopedia of Wood Joints" and while not exhaustive, it has a larger smattering of joinery.

    The most disappointing aspect of that book is it doesn't have relative dimensions or generic rule sets for layout.

  7. #7
    Join Date
    Jan 2019
    Location
    Fairbanks AK
    Posts
    686
    I have heard of that called a "fox joint" with a single wedge, but when I internet searched it I found plenty of fox joints with two wedges. Interesting.

  8. #8
    Join Date
    Jul 2007
    Location
    Inkerman, Ontario, Canada
    Posts
    825
    Th first entry door entry door commission, probably 45+ years ago, long be "iPhone calculator trig" and long before I had much equipment. Solid Oak fox wedged mortise and tenon joints in the door and pinned mortise and tenons in the frame. Brushed on varnish finish. The last photo of the oak door is before delivery and without the transom glass and brass mail slot. Didn't take many photos back then and what i have are pretty bad.


    21.jpg 019.jpgProfil53.jpg

    I did a few after that one, but switched to pegged mortise and tenons, as in this cherry one below.

    Profil51.jpg

  9. #9
    Join Date
    Apr 2017
    Location
    Central NC
    Posts
    134
    Love the proportions of that cherry door/entry way Mark.

  10. #10
    Join Date
    Jul 2007
    Location
    Inkerman, Ontario, Canada
    Posts
    825
    Thanks Michael. Entry doors are great projects to do.
    Quote Originally Posted by Michael Todrin View Post
    Love the proportions of that cherry door/entry way Mark.

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