Tenon Design Question
#6
For table or bench legs, why do we cut 4 shoulders?  Are the two shorter ones all that useful? I am thinking specifically about legs that are wider in one dimension. I the tenon is /13 leg thickness, then would not cutting some tenon length (to create the two smaller shoulders) reduce tenon strength without adding much in the way of top support? Cutting the little shoulders would seem to gain little - just the 1/3 tenon width for however much one cuts off the tenon. I'm really thinking more about bench legs than tiny tapered legs on a tea stand.
Thanks,  Curt
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"Life can only be understood backwards; but it must be lived forwards."
      -- Soren Kierkegaard
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#7
(02-20-2020, 01:20 AM)cputnam Wrote: For table or bench legs, why do we cut 4 shoulders?  Are the two shorter ones all that useful?  I am thinking specifically about legs that are wider in one dimension.  I the tenon is /13 leg thickness, then would not cutting some tenon length (to create the two smaller shoulders) reduce tenon strength without adding much in the way of top support?  Cutting the little shoulders would seem to gain little - just the 1/3 tenon width for however much one cuts off the tenon.  I'm really thinking more about bench legs than tiny tapered legs on a tea stand.

By making 4 shoulders the mortise dimension does not have to be dead perfect. The shoulders hide small imperfections . 
mike
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#8
I had always thought like Mike, the shoulders hide some sins, but on bench legs....who cares??? For working pieces I'm very much function over form.
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.
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#9
Same as mentioned above.  But I'll add that the 1/3 "rule" only applies to hand chopping mortises.  You can gain strength in 3/4" stock, for example, by cutting a 3/8" wide mortise with a router or chisel mortiser instead of the traditional 1/4" width chopped by hand.   1" stock gets a 1/2" mortise instead of 3/8", etc.  

John
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#10
Thank you, gentlemen! As you may have suspected, the legs in question are a 3 part glue-lam for which the centerpiece becomes the tenon. Just could not figure out why I would want to weaken the tenon since aesthetics are not part of the equation. Had enough trouble perfecting the two shoulders I've got now.
Thanks,  Curt
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"Life can only be understood backwards; but it must be lived forwards."
      -- Soren Kierkegaard
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