David Marks and Loose Tenons

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David Marks calls them 'Loose Tenon'. As does Gary Rogowski in his book JOINERY.
http://www.djmarks.com/stories/djm/Loose_Tenon_Joinery_90627.asp
Above is a link to Marks's web page with an explanation for his madness. I found it AFTER i posted my question.

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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.
http://home.comcast.net/~charliebcz/MtPrimer4.html
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 joint.
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)
charlie b
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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?
--

-Mike-
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The rates that we

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 mortise.
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 joint.
Glue or surface fiber will eventually succumb, but the M/T will still bear load in design direction, and if pegged, should not withdraw.
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Joinery That Held Together for Thousands of Years vs 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.
Interesting discussion.
charlie b
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And the diagram on your web site is one of the best I've ever seen. I'v bookmarked the site. Thanks.
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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 unconstrained.
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 from moisture.

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 different issue.

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.
--

-Mike-
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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.
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mike hide wrote:

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..
charlie b
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Versus Apple's Macintosh. ;-)
Kevin
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wrote:

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.
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mike hide wrote:

If you double draw pegged them they wouldn't
charlie b
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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
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<snip>

Mike,
Were you criticizing integral tenons, improperly fitted?
Because I was thinking we were discussing what is sometimes called a 'floating tenon'.
I'm loathe to have an argument where there is no disagreement. ;-) Those I can find at home.
Patriarch
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