David Marks and Loose Tenons

[Lobby Dosser]

And the diagram on your web site is one of the best I've ever seen. I'v bookmarked the site. Thanks.

[mike hide]

[mike hide]

Thanks for the kind words, at times like this it is good to have a bribable brother who does not have the same last name ...mjh

[mike hide]

It is even better if the square pin is the same width as the hole diameter then there is no chance of splitting. I have chairs made in the 1730s that have pegged tenons and they are as tight now as the day they were made .the offset between the motice and tenon hole is about 1/32" to 1/16"...mjh

[Mike Marlow]

Right after kickback safety and sawstops.

[Mike Marlow]

"George" wrote in message news:42930f6e$1 [e-mail]...

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 hide]

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

[George]

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

to read. Start with chapters 2 and 3.

[John Santos]

I've noticed that David Marks always seems to use the same wood for the tenons as the pieces he's joining. I wondered if that was the reason why, or if it was just because there was usually plenty of scrap available. But why else use something expensive for the tenons since they don't show? Is there another reason or is it for stability?

(He also always veneers both sides of his base stock, and has explicitly said that's for stability, but often uses a different (nice, but cheaper) wood for the side that doesn't show.)

[Duane Bozarth]

John Santos wrote: ...

I would expect he does it for all the above reasons. It certainly is "safer" to use the same material from the standpoint of reliability. The amount of material used is insignificant in terms of saved cost. Plus, he may (probably is?) like many of the rest of us--whether it shows to anybody else or not isn't material-- knows what the interior is.

A similar case is wiring inside a wall--many make it as neat as they can "just because" even though it all gets covered over and the electrons don't care...

[Larry Jaques]

Stability, but there's always scrap which can be used from each project. By using the same wood in the same grain direction, he keeps from having any trouble with different expansion rates. His loose tenons don't explode the wood they're in during the humid seasons.

Right. It lessens cupping.

[Patriarch]

Duane Bozarth wrote in news:42972420.7B6094D2 @swko.dot.net:

And another thread devolves into an electrical wiring discussion... ;-)

[Duane Bozarth]

Oh, you're now saying the electrons care??? :)

[Kevin Craig]

Versus Apple's Macintosh. ;-)

Kevin