For those of you who don't get abpw:
Rough sketch of chair leg and rail (legs angled 7 degrees from vertical)
I know what I _think_, but which "floating tenon" joint to YOU _know_ to be
stronger and why?
Actually, with "A" there appears to be more "material" for "strength" at the
top of the rail/stretcher, where you (not "you" personally, but a
non-engineer for sure) would think it would do the most good:
... and would an 1/8" at the bottom make that much difference?
While I tend to agree on the surface, that's actually been proven to not
make much difference, if any, and certainly a "real" _angled_ tenon could be
much less strong depending upon the grain of the particular piece.
The jury is still out ... :)
> "Chris Friesen" wrote in message
>>I would go with "B".
I'm to lazy to do it for you but if you calculate the section modulus
of each joint, you'll find "B" is stronger.
S = M/Z
S = Stress
M = Bending Moment
Z = Section Modulus
Z = I/d
I = Moment of Inertia
d = Distance from centroid to outermost fiber.
I (for a retangle) = bh^3/12 = 1/2ad^2
b = base
h = height
a = area
d = distance from center of area to center of bending moment.
Any decent strength text will give you the formula for a circle.
(Dredged from my memory from all those strength of materials classes
taken so long ago.)
I tried to cancel that post, but I guess it got through anyway. The
racking resistance with shoulders will be fine (possibly better), as
long as the tenon doesn't pull out or the shoulders fail.
"A" has the advantage that the mortices are at right angles to the ends,
making it simpler to mill.
If you're looking at a "production" run, it really might be worth
testing both designs to failure.
Bingo ... and therein lies the reason for the question. :)
Yep ... a limited production run, in a space limited shop (but with plenty
between the ears, some would say), by a time limited wooddorker, wanting to
test the limits of angled "loose tenon" joinery.
Actually, both are doable, and while I've already cracked the "B"
methodology with a homemade jig, "A" is easier, and much, much more
"precise" (at least without that JDS Multi-router I keep threatening to
... and in joinery, precision often trumps even a tiny bit sloppy, with
regard to strength.
Thanks for the input, Chris.
I don't think so. With B the rail would be clamped vertically and the
mortise made vertically, the angle is irrelevant. To do A you've have
to hold the rail at an angle. The leg is maybe harder depending how
the mortise is made. Not very difficult to tilt the table on a drill
And I cast another vote for B being stronger. You've got more
uninterrupted long grain on the end of the rail.
If you precut the rail/stretcher end to the required angle (7 degrees in
this case), they (leg and rail) are both easy, 90 degree plunges.
"B" is trickier, less precise IME, and requires a much longer bit.
Yeah, but.. it clamps to the sides of the rail right? So what
difference does it make what angle the end is at, other than that if
you don't want the mortice parallel to the sides it has to be able to
compensate for the angle?
Good question. I've put some pictures up for you.
Go to the url below and scroll down to "Router Mortising Jigs" and you'll
see the simple jig that allows you to do this:
Let me know if you have any questions.
OK Swingman, I have to make these remarks.
I have worked in various communication capacities and have had to evaluate
marketing materials and corporate communications. I had to constantly fight
the artsy fartsy graphic designers who can take any simple communication
task and turn it into a psychedelic nightmare. I remember when a newsletter
was a page or two of typewritten information that you could use.
Your website is a marvel in simplicity. Both in terms of design and
communication. You use pictures to illustrate what you are talking about.
You give short, concise messages with the pictures. And you do so in a warm,
folksy manner that is such a refreshing alternative to the marketing centric
styles of so many other websites.
And it chronicles a guy who has a simple, small shop. There is no big
warehouse or commercial shop here. It gives information freely to ordinary
folks who want to create or expand a home workshop. I have your website in
my favorites list. And I recommend your site to others.
Just wanna say, good job sir. If more folks did such a good job as you with
their website, the web would be much more enjoyable (and educational). It
makes the whole putting together a shop thing more do-able. It is a
pleasure to peruse your website.
Now I gotta go back to being my usual curmudgeon self.
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