Thread: Dovetails without Glue

dovetails were stronger (pulling through the tails) without glue than with glue (due to the ability of the wood to squeeze and deform into the gaps between the pins.

Is it the same as saying dovetails are weaker with glue than without glue? I find it very hard to believe.

I think I'm with Wongo.

Probably started as a way of fixing sloppy joints and then some bright spark realised if you cut them all like that, it makes it easier to assemble a carcass.

As for the glue vs no glue, I think I'll stick to glue if it's all the same

No it's true, the report is sound, and the picture in the report is very telling in explaining why it happens that a glued dovetail is weaker. My opinion is if you want to explore this for practical reasons then you're engaging in some kind of self abuse. They don't say in the report what the failure load is for the glued dovetail but surely on the weight of evidence from sound antique drawers, it's hardly a practical consideration. You would need drawers stuck so fast that you crow bar them open to impose the kind of force needed. If you want to do it for academic interest then that's an entirely different matter!

the picture in the report

Linky?

Originally Posted by silentC

Linky?

Oh, it's in the quote thrown up in the last link of Paul's OP.

OK yep makes perfect sense. Like grabbing a bunch of straws tightly and having someone try to pull one out versus holding them loosely. Friction between the fibres means they share strength and spread the load.

I'll still glue them though. I'm more concerned about them coming apart the way they were put together, than being ripped out by the roots like that.

They should repeat the test with the force perpendicular to what they used there and see how long the unglued ones last

The lengthy quote from the comments section of the CS blog:

Chris,

I am pleased to see that you are interested in what I call wedged dovetails. They have been an interest of mine for a number of years, ever since I was lucky enough to help restore a pipe organ
built in Pennsylvania by David Tannenburg, America’s first organ holder. The case was expertly made in a strong German tradition with a great number of dovetail corners . Every pin was neatly wedged. I felt that surely this was not some cabinetmaker covering up hundreds of miscuts, but rather an important trade practice. My apprentice training was mid-late 18th century English and I had never seen this before.

Since then I have looked at dozens of chests and case pieces from the 18th and 19th centuries and
have been struck by how many of them have their pins wedged. I would say for the typical Germanic background chest, painted or not, the vast majority have wedged dovetails. When asked about this, museum curators will say the wedges were for tightening up loose joints. Period woodworkers will say the same thing, even though the possibility of miscutting every single joint in a chest stretches the imagination. Nevermind the fact that the boards should be split wide open from so many wedges driven into them.

I believe that there are several very good reasons for the wedged dovetail joint. The answer became clear to me when I thought about David Tannenberg and his dovetailed organ case. Now we are talking about pieces 8 and 12 feet long, almost 2 feet wide and near 2 inches thick. I don’t know about you, but I get more than a little anxious just gluing up a little dovetail box what with all the glue to spread, clamps with special shaped pads, square to check for, etc. etc. And that’s all with modern slow setting glues and a warm building. Hot hide glue and a chilly shop! Help!

The secret to a wedged dovetail is purposefully cutting the tails out of square. In other words, not sawing at right angles to the face of the board, but tilting the saw first one way then the other so the socket is wider on the outside than on the inside. The pins are cut as usual, except that each one gets a sawcut right down the center . Now the joint can be assembled dry with no glue. It goes together with hardly any effort since the joint is slack everywhere except at the very bottom, where it can be quite tight.

At this point the chest is completely together, no clamps , no glue and no banging on tight fitting dovetails. Glue is brushed into each opening , then a wedge driven in which spreads the pin tight against the dovetail socket and at the same draws the joint down against the shoulder, completely avoiding the need for clamps. Each corner can be done individually. In fact, every pin/socket can be glued individually. You could stop and have lunch part way through if you wanted to.

The ease of assembly is a by product of the main feature of this joint. It solves the one drawback of a “regular” dovetail corner. Rather than relying on glue and a tight fit to be strong in the direction of assembly, the joint is now mechanically strong in both directions. You wonder if they used glue at all. II have looked closely at old chests made like this and while most of the time it was not possible to tell if there was glue or not, a few of them showed glue on their insides, where it was not necessary for it to be cleaned off.

If you would like I can try to post some close up pictures of antique chests with this style of construction. Especially interesting are shots showing the out of square cuts on the dovetails, and how surprising large the wedges are.

I believe this is a very important trade practice that has been misunderstood and therefore overlooked in the museum/period furniture world. Many questions immediately come to mind. Some are easily answered, some not.

Perhaps this lengthy post will start a discussion that will shed more light on this intriguing woodworking joint.

OK, there are some very persuasive points in that quote

Any chance to see the pictures?

Thanks

Originally Posted by axe

Any chance to see the pictures?

Thanks

Wedged Dovetails

Woodwins: Wedged dovetail pictures

More.

Wedged Dovetails | millcreek woodworking

https://dl.dropbox.com/u/2169961/IMG_0389.JPG

https://dl.dropbox.com/u/2169961/IMG_0391.JPG

Toby

Dovetails without glue? Well I am sure that wedges done correctly would work. But I have cut a lot of dovetail joints and I have glued all of them. I have never seen one fall apart. So if I was making joints without glue it would not be for strength but for fun.

Originally Posted by chook

So if I was making joints without glue it would not be for strength but for fun.

Or on principle. Or by necessity.

I think there are green-wood chairs that are designed around the shrinkage in the wood tightening the joints (?)

And certainly oak timber-framing employs pegging (is it draw-boring?) and shrinkage and (I assume) no glue. Also the various forms of 'log house'.

I had that quote above from Alan Peters that wood moves and glue only lasts so long, and that he had his eye on the several centuries mark.

So ... I don't think it's not worth thinking about.

There must be a world of joinery/construction techniques without glue ... either antique or still employed ... from Europe/Africa/Asia ... maybe in remote areas ??

Cheers,
Paul

It occurs to me (now) that round chair tenons may be split and wedged, as also the standard (square mortice and) tenon.

And somewhere in the outside links I read someone say they finish nailed their dovetail joints.

Also I'm not clear whether the Greene & Greene pegged joints are structural or decorative.