This is what I was worrying about. This sounds like the best of both
worlds then - a tight fitting dry joint is a pleasure to produce (in a
wierd sort of way) and should hold well too!
I assume this is also glue independant? For now I'm using TiteBond ..
Well, it's not all that you think. The word "snug" is best, I believe, in
describing the dry fit. Water-soluble glues expand the fiber almost
immediately, so don't dawdle over assembly.
Oh yes, the plastic will keep the area expanded as it solidifies, so you
really can get by with a little less than a press fit.
While I agree with all the posts, I'll add one item: the surfaces should be
smooth. I can just a joint on the bandsaw that slides smoothly together
without slop, but the rougher surface just won't be as strong unless the glue
is sufficiently gap-filling and enough is applied.
Still and all, most well-made glue joints are stronger than the wood itself. I
compared MT joints with the mortice from morticing bits and the tenon on a BS,
against routed mortice and TS tenon. Angled strain broke the wood in both
cases. However, repeated back-and-forth pounding loosened the former while the
On Mon, 21 Feb 2005 17:07:07 -0700, email@example.com wrote:
Good point and one I hadn't thought of. How smooth *are* the mortises
from a mortising machine? Maybe on a related thought, are mortises
stronger with rounded corners (routed) or with square corners?
Intuition would tell me that a rounded M&T would have fewer stress
points and would therefore be stronger, but intuition is often wrong.
M/T has shear strength based on the tenon depth and wood strength. Shape of
corner unimportant. What's important is that the tenon should mate with the
bottom of the of the mortise in the load direction. Can be loose as a goose
Racking stress depends on a firm register of the shoulders of the tenoned
member against the mortised member.
Unshouldered tenons should fit and bottom the mortise to take best advantage
of the anti-racking available by having some resistance at right angles to
the tenon itself.
and charlie b added:
the following may make George's points clearer
wood expands more, a lot more, acrossed the grain than with the
A mortise and tenon typically joins at 90 degrees (+/-). If the
fits the opening snug all the way around, the dimension of the
won't change much, the depth of the mortise might but that's not
a problem. The tenon, on the other hand, can expand or contract
of the cross grain on the critical, largest cross grain height
Leaving a little room on top gives the tenon some room to move.
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And here's some more on "fit", including "spit tight".
M&Ts seem so easy and straight foreward - until you think
about it a bit - or try to make some good ones. Them old
woodworkers were pretty smart - and skilled!
Hope this helps.
Good stuff all the way around. I guess there really isn't any reason
to square the corners of my mortises when I cut them with a router. It
is dead simple to make the tenon fit the rounded corners and a bit of
a pain to make the mortise square, so with no structural reason to do
it differently I'm voting for round ended M&Ts unless someone provides
a practical reason or if I'm doing a through tenon.
I just browsed around a bit on charlie b's site. There are some
interesting thoughts there ... probably old hat to you pro's but this
beginner is pushed into thinking a bit about what he finds there.
Thanks charlie !
Charlie's site like a pretty good reference for many to start with. As was
mentioned, there are very few articles that go into enough detail. However,
keep an eye open for articles by Ian Kirby. He goes into more details of
joinery than most.
A little confusing, though, on his mortise/tenon-first page. He says he cuts
the tenon first, then goes on and gives another reason for cutting the mortise
first. I agree with his comments, but I'm not sure which his conclusion is.
For most cases, I used to always start with the mortise. Moving to router
template jigs, however, it no longer matters since I get exact duplicates
(provided I don't flip the reference faces, of course).
Geez, and I thought I was like The Pope - inflammable. Sorry - it
a Thinko (mental equivalent of a typo) and it's been fixed.
mortise first -yeah, mortise first. K-Mart sucks, yeah.
Sorry about the confusion. My bad.
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