Which is stronger?

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Swingman wrote:

In "A" a considerable portion of the sides of the mortise in the stretcher is short-grained and prone to splitting.
"B" does not have that flaw. "B" is stronger.
--

FF


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post hoc, ergo propter hoc? ... a 7 degree difference in grain direction would not be uncommon in any angled tenon.
But I tend to agree with you ... grain direction appears to be a key factor.
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The saga continues:
http://www.e-woodshop.net/Projects10.htm#Joinery1
Using "B" has always been my preference, particularly once I found a source for carbide end mills of sufficient length that could be used in a router.
... nonetheless, the JDS Multi-Router is looking more attractive all the time.
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I'm not really for either as they stand but might go with a variation of "B", in what I'd call a double secret probation - uhh, wait a minute - a "Double Secret Wedged Tenon".
Usually a wedged tenon is a show joint but you can do a secret one by undercutting the edges of your mortises by the seven degrees described to form a kind of keystone shaped hollow.
Cut your wedges to fill that seven degree void once they bottom out on the mortise. Cut the appropriate slots in the tenon. Butter the tenon and the wedges up and insert the wedges just barely. Drive the loose tenon home to form a dovetail within the keystoned void. Prep the other end of the tenon the same way and clamp her up.
You'll wind up with opposing dovetails.
Dat sumbitch be strong.
Regards,
Tom Watson
tjwatson1ATcomcastDOTnet (real email)
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"Tom Watson" wrote in message

I reckon ... excellent, vivid description. Thanks, Tom.
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Ya know, Swing, like most joints, it prolly talks harder than it cuts.
I don't think it will slow you down any in production once you get through the Goldilocks process of, "Too Tight, Too Loose, "Just Right".
All new joints are a process until you get to the point of, "Fire For Effect".
I believe it would be a damned strong joint, with little extra time involved, once the jigging was perfected.
It sounds like you are trying to use a router.
I'm not big on round-shouldered joints, regardless of the gluing surface presented.
I'd use a morticer and be done with it.
I like the lock of the right angled shoulder, and with a joint that is not haunched, I would particularly look for some right angles in the joinery.
Just my opinion.
As always YMMV.
Regards,
Tom Watson
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"Tom Watson" wrote in message

I feel the same way, but wanted to explore something different for the angled and compound angled joints this time around. Most of the other joints, and there's a ton of them in the back and seat, will be cut with a morticer.
Been reading too many design tips lately. Seems like the current philosophy is to design first, then figure out the joinery after the design is cast in stone.
My first question when I see a piece done that way is "Yabbut, how long will it last" ... with FLW's falling down "Fallingwater" in mind.
Right now I've got a belt on, but I'm still looking for those suspenders ... looks like you've found a pair
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I've always been a fan of form following function. I have enough ego that I would not like to see a difficult to achieve joint hidden.
I don't know what your constraints are on the design level, so I responded with what I thought would be a strong joint for the given conditions.
If I had my way, I'd show the wedged tenon, rather than create a hidden version. I never really liked the idea of "Secret Mitered Dovetails" for the same reason.
I didn't like the "A" version because it violated my sense of joinery, which includes the notion of eliminating as much short grain as possible.
I'm conversant with the arguments for loose tenons but there is something about them that sticks in my craw. I'd rather see an honest tenon on that rail or stretcher, with an exposed wedged tenon. It seems more craftsmanlike to me.
Some smart fella said something along the lines of, "Joinery is the beginning of ornament".
All I can say is, "Amen".

Regards,
Tom Watson
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Tom Watson wrote:

ISTR that those are called fox tenons.
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FF


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My credentials: degree in mechanical engineering with a specialization in strength of materials. Formerly a licensed professional engineer in the state of Illinois. Based on the rough drawing, if you made 10 of these joints each way and tested them to failure, I'm not sure you could measure a statiscally-meaningful difference between the two. Now, I haven't spent all night thinking about it, so if someone can make a persuasive argument to the contrary, I'm open. So with that said, offhand I'd go with the one you find easier to machine.
todd
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"todd" wrote in message

a
all
the
find
Very impressive, Todd ... and I appreciate your input. My gut feeling is that the "easiest to machine", which is also the most precise in this case, might mitigate any slight strength issues over a run of parts, particularly if the joints are pinned as planned.
Right now I'm in the process of "jigging up" for a prototype and still have a good deal of freedom in methodology.
Thanks again for taking the time to respond.
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Civil eng (Structures) with one old prof that used to toss the textbook and point out the basics occasionally.
If it was an isotropic material, I might agree, but it's wood and the grain will dominate the behavior. Wood can exhibit significantly different strengths depending on orientation relative to grain.
How that joint will behave will depend on factors beyond just the wood or the orientation of the tenon. If the joint is glued with a seriously stiff and strong adhesive that prevents any motion in the joint, either will be strong. If the adhesive can flex, the shape and orientation of the tenon will affect the overall strength (given the grain). Since I've seen more joints fail due where no strong adhesive is used or the adhesive lets go, I'd tend to design ignoring the adhesive and then B is stronger. I wouldn't go with a tenon crossing grain lines significantly. If the tenon in the drawing is to scale, then the rail is thin on the periphery - Use B.
If the wood selected has crap grain, either A or B would be equally weak.
Mike
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Michael Daly wrote:
> Civil eng (Structures) with one old prof that used to toss the textbook and > point out the basics occasionally.
You had one of those to huh?
Mine wasn't old, just a slave driver.
I still remember his tag line, "Gentlemen, get out your coolie hats, it's time to go to work."
Lew
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