David Marks calls them 'Loose Tenon'. As does Gary Rogowski in his book
Above is a link to Marks's web page with an explanation for his madness. I
found it AFTER i posted my question.
Accidently sent this to Mike instead of here. So -this is sort of
like trying to hold a conversation with a 10 hour delay between
parties. Hopefully the diagrams that show the six degrees of
freedom of movement which must be resisted and which parts
of the M&T joint resists which movement.
This may clarify things a little - showing the six (yup - six) degrees
of freedom of movement that need to be fixed if two pieces of wood
are to be joined together and not come apart. A mortise and tenon
joint resists 5 of the six.
As for having a "sloppy joint" - there are instances where a little
"slop" actually can be a good idea - a table apron to leg joint for
example. Having a little slop at the top of the tenon gives the
tenon a place to expand without blowing the top of the leg off.
You've got vertical grain for the legs and horizontal grain
for the apron. The cross grain in the tenon will expand more
than the vertical grain in the leg. If there's not place set
aside for that expansion it will try anyway. The tenon will
either compress and get tighter OR it will make the space
by moving some wood above it at the top of the leg.
It seems "spit tight" is what to shoot for. The tenon should
fit snug enough to go in and out with just moderate hand
pressure - no dead blow hammer, no mallet whacking etc..
But if you spit on the tenon and then seat it, it should
swell enough to make getting the joint apart difficult.
And tight also means leaving some place for a) glue inside
to go (mortise a little deeper than the tenon is long) and
b) some place for compressing the air trapped in front
of the tenon as it seats or someway for it to get out of the
The beauty of "traditional joinery" is that it lets you
dry fit things and the parts will a)self align and
b) be self supporting. That's real handy if you make
things "on the fly" - make step 1, make parts for
step 2 to fit what you have in step 1 and so on. Has
the advantage of letting you see things at full scale
each step of the way.
If you've ever worked from a "plan" and cut all your
parts BEFORE putting them together you know that
somewhere amongst all the given dimensions there's
at least one that's wrong. Working progressively
you can get dimensions off what you have. It isn't
important that a part be 22 31/32nds but rather
that if fit between the parts it's suppose to fit between.
I can "take the line", "split the line" and "leave the
line" more often than I can read a tape properly ; )
(ok - tell me you've never made a part an inch short)
This is where all of the discussion here about wood swelling with moisture
etc., goes a little astray. First off - yes it does swell with moisture, I
am aware. But... look at the myriad of jointery around you that has
survived decades or longer without suffering the expansion problems that are
talked about here so frequently and ask yourself what is wrong with this
picture that there is so much discussion about 1/8" of movment across grain,
or 8% humidity, etc. but there are so few broken joints in the furniture
around you. We get so focused on one aspect of things that we sometimes
overlook everything else. Sure, moisture causes swelling - to exposed and
uncontrolled wood. Wood that is secured as a tenon in a mortice does not
absorb moisture in the same way that unsecured wood does. The rates that we
see published for wood expansion and moisture absorbtion are for raw,
unsecured wood. They do not apply to sealed wood and they do not apply to
wood that is secured as in a mortice and tenon. The mortice acts to keep
the tenon compressed such that it can only absorb a certain amount of
moisture, therefore a very controlled amount of expansion. Throw it under
water if you want, but unless the glue disolves, the joint is not going to
fail due to moisture absorbtion until the entire asssembly absorbs enough
water to distort the whole piece. That would be far more than you'd ever
see in environmental changes. Joined pieces of wood (with such interactive
techniques as mortice and tenon) are simply not the same as raw wood and do
not behave the way wood charts would imply for moisture absorbtion. Once
again - look around at how few joints you can see that have actually failed,
and then look to see why they failed. Most did not fail due to the joint
being too tight and not allowing for moisture absorbtion.
That does indeed make for a nice, precision fit, but it would not be correct
to suggest that a dead blow tight fit is somehow less strong or long lived.
I have put many joints together that took some pretty good persuasion to
fit, and years and years later, they are still there, just as they were when
the project was built. I have to admit, when I have to resort to a little
persuasion, it's generally because I'm rushing it along in some way and
simply did not want to spend any more time to make it that little bit more
perfect - but - the joint does not fail.
I agree but I generally find that all jointery has that required amount of
slop just by the nature of the woodworking and the material at hand.
Now that's a man that's talking some good stuff!
All right Charlie - you've been looking over my shoulder, haven't you?
You are incorrect. The fibers will expand and contract when the moisture
gets to them, and at the same rate, less compression set. You may slow the
arrival with occlusive finishes, but wood loves water and will find a way.
The reason M/T joints work loose is related to this reality. What went
together "spit tight" at 12% MC is less so at 8 or 4. The joint may then be
subject to racking strain, compressing some contact areas which will make
the joint sloppy even when the MC returns to 12%. That's why the glue and
pegs - to deny motion even when the tenon tries to become smaller in the
Works the other way, too, though more slowly. Joints made at 4%, if the
don't split the wood getting to 12, begin to develop some compression set
which remains after the cycle returns to 4, progressively loosening the
Glue or surface fiber will eventually succumb, but the M/T will still bear
load in design direction, and if pegged, should not withdraw.
Joinery That Held Together for Thousands of Years
A / C
I grew up in the tropics, the place formerly known as the
Panama Canal Zone (sounds sort of like the artist formerly
known as Prince), where the temperature ranged from
maybe 78 degrees up to perhaps 94 degrees. The humidity
stayed in the 90 to 100 percent range because the Isthmus
is only 50 miles wide with a lot of water on both sides
(we only had two seasons, Dry Season and Rainy Seasno.
.Dry Season usually was on a Thursday).
I grew up with solid wood, (teak, mahogany, rosewood,
cedar etc.) often carved, furniture from India and China
- all done with traditional joinery, and some quite
complicated and all done with hand tools. Even the delicate
stuff hung together well UNTIL air conditioning became
available. Within 2 years the joinery started opening up
on the more delicate stuff and a drop lid desk with drawers
had the lid warp and split, stretches get loose, drawers get
loose etc. The range of change in relative humidity and the
resulting change in % MC was just too great for the joinery,
given that it was probably made with a %MC of 14 - 18 and
in an A/C environment was probably down to 4%.
For some reason, some of the Chinese furniture, the ones
with triple mitered corners, frame and panel with mitered
frames held up despite the AC.
So, I'm guessing that it's not wood expansion that I need
to accomodate, but rather wood shrinkage - at least for
"house furniture" (as opposed to "just shop furniture").
Guess I'll shoot for Spit Tight rather than Snug or
CTSBTF (Cut To Size, Beat To Fit).
Oh, BTW - if you're going to use half blind dovetails
for a wall hanging tool cabinet, DO NOT put the pins
on the sides and the tails on the top and bottom -
especially not the bottom! Nails, even finishing nails,
detract from the dovetails - just a little bit.
This does not make sense George. Wood fibers that are constrained can only
absorb water to the point that they equal the force placed on them by the
joint. At that point they effectively reach their saturation level. Wood
does not continue to obsorb moisture until it reaches the point that its
moisture content is equal to the surrounding air, it absorbs it to a maximum
it can hold and that maximum is limited by the cell's ability to contain
that moisture. Constrain those cells and they are capable of holding less
moisture. Like I said, look at how many mortice and tenon joints have held
up for decades and longer without showing effects of changes in humidity.
Look at wood that is nailed in place. The wood does not move between the
nails, it moves where it extends beyond the nails. It moves where it is
If you could wring out a piece of wood what would happen? Just like a rag,
it would lose its water due to the squeezing process. Cells and fibers
under pressure cannot hold the same amount of moisture that cells and fibers
not exposed to the same pressures can. Wring partially and you evacuate
some of the water, wring more and you evacuate more until you reach the
point that you evacuate all of the water that you can under the pressure
that you're able to exert by wringing. Likewise with wood. Fit tight
tenons and the increase in moisture will only swell the wood to the point
where the pressure exerted on the mortise and the tenon does not exceed the
cell's and the fiber's ability to hold water. The tighter the joint, the
less this ability. Both the mortise and the tennon are going to expand from
the increase in moisture, and both are going to contract by the absence of
it. Looser joints will allow for more movement resultant from the changes
but in either case, the wood is going to be constrained in its ability to
absorb moisture by the pressure exerted on the joint, by the joint. Fit the
joints tightly, and you create a joint that effectively reduce this movement
to the point where it is negligable. There is too much joinery out there
that does not open up gaps in dry weather and close up tightly under higher
humidity to deny that the pressures exerted on wood does not affect movement
This agress with what I said originally, and with what I elaborated on
above. My point originally was that the pressure factors on the joint have
as much or perhaps more to do with what these movements are than relative
humidity does. I suggest that we find way more mortise and tenon joints
that work loose from mechanical stresses (think of a dining room chair) than
we do from wood movement related to moisture levels. That mechanical stress
works the joint regardless of the moisture content. It's an entirely
This is the point that I suggest is less of an issue in the real world than
is often discussed. I suggest that within certain limits these conditions
will not have the adverse affect on the joint that is often suggested. This
of course, assumes that the joint is constructed reasonably correct in the
first place. The joint has to enjoy mortises and tenons that are
constructed of the proper proportions in the first place. That assumption
allowed, the joint will not see moisture levels vary as much as a raw piece
of wood will. The expansion and contraction within the joint will be much
less than the tables attempt to indicate.
This is why wood products of all sorts can be and are, shipped from all over
the world to all over the world, and do not fall apart. These products are
around us every day of our lives, everywhere we go. The proof of this is
easy to see.
My point does not suggest that moisture content is not a factor to be
considered in woodworking and in joinery, rather it is that this one factor
is too often spoken of in isolation and not considerate of other factors
that play into the issues of wood joinery. Moisture tables are only part of
the story, and like everything else, they need to be taken in a context.
What I've tried to say in this conversation is that interactive joints such
as a mortise and tenon are affected by factors other than just what is
suggested in the moisture tables.
It does to wood technologists. RH correlates directly to moisture content.
Wood fibers that are constrained can only
Incorrect again. The fibers adsorb moisture at the molecular level, binding
to the cellulose. There is a lot of air left inside any board, indeed,
inside the cells themselves, which spaces are shrunken by the inexorable
gathering of moisture, though they do compression set - they don't return to
full expansion - which condition exacerbates the one caused by shrinkage of
the fibers themselves once the wood begins to seek EMC with lower RH.
Wonderful, well-documented stuff here
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm to read.
Start with chapters 2 and 3.
Nope - it's about an end grain to edge grain mortise and tenon
joint that puts a mortise in both parts and then a separate
piece of wood to go into those mortises.. "Loose' menas that
the tenon is not part of either piece to be joined together..
Were they drawn together by offset holes for the pegs? I have
furniture done with that technique that's never moved or had to be yet
adjusted. They built barns and ships that way. The M& T are snug,
but not dead tight, just drawn tight.
I am not familiar with the term "double draw pegged" What I refer to is the
standard practice of chairmakers at the time was to bore a hole normal to
the mortice insert the tenon and "spot" the hole center on the tenon .Then
remove the tenon and bore it with the same drill a thirty second or so
closer to the tenon shoulder, so when the peg [usually square] is inserted
it draws the joint together tight....mjh
Were you criticizing integral tenons, improperly fitted?
Because I was thinking we were discussing what is sometimes called a
I'm loathe to have an argument where there is no disagreement. ;-) Those I
can find at home.
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