Thread: The World's Strongest Dovetail Joint

Hi Luke

there's as strong as possible and then there's as strong as needed.
strong as possible would have equal width pins and tails, strong enough would be achieved with a 1:2 ratio for the pins and tails.

my answer is choose a width that matches the width of your widest chisel.

Pins and tails don't need to be even width. Especially because it will be covered by a molding, I'd layout the joint out by eye -- you don't want someone accusing you of using a router and DT jig.

Luke, when laying out carcase dovetails, I start with the tails board, as most do. Using my my dovetail marker-outer, I start with the first tail the width of the marker (~15mm), the next a bit wider, the next a bit wider again, until I'm around an inch from the centre (plus/minus). I then repeat the sequence from the other side of the board. All done by eye, no need to fuss with dividers unless you are the obsessive type; you won't see any small discrepancies, & if you follow the time-honoured practice of tracing the pins off the tails, you shouldn't end up with too many gaps.

It's an expedient way of setting out, and I do have a reason for putting the closer-spaced tails at the edges. It's because the outside pins & tails cop the most stress, either from the case being tipped onto a corner, or the wide boards wanting to cup with seasonal movement, so putting a bunch of solid but closer-spaced pins & tails at the outsides adds extra glued surfaces to help counter that. But it's mostly because I simply prefer the look of the varied spacing - even spacing looks boring & machine-made, to me.

As ian said, there's 'strongest' & 'strong enough'. Intuition & experience tell me that a set of 1 1/2" tails with pins of about 3/4" across an 18" board would do the job plenty well enough, if you preferred to keep them even....

Cheers,

Thanks, fellas.

End of the day, I'm probably overthinking it, and sometimes having that notion validated is the most important part of developing one's techniques .

I admit I've become a bit of a slave to my dividers, mostly given the fact that I'm usually laying out visible or semi-visible (think drawer) dovetails. but, given that these are wholly concealed, I may give the dividers a break when I lay these out. I like the idea of going rogue from time to time.

I think this should be the last of my conundrums on this particular project. These high society type pieces require a bit of extra agonizing, ya know?

Cheers,
Luke

Originally Posted by Luke Maddux

...... These high society type pieces require a bit of extra agonizing, ya know? .....

I most certainly do! A couple of my pieces took literally years to complete, for various reasons - far too much time to mull over and vacillate on all sorts of details. I suppose the intelligent approach would be to get hold of, or create, a full set of working drawings & just follow them to the letter, but it wouldn't be as much fun that way, would it?

Cheers,

Strong dovetails you say.
http://www.ironbridge.co.uk/collecti...e-iron-bridge/
Regards
John

Luke

Your heading certainly got my attention as it took me back more than fifty years to when I was at school and the English master asked us to describe what "hyperbole" meant. The first few kids gave unsatisfactory answers and then I was called upon to give my definition.

"Rhetorical exaggeration" I confidently proclaimed. The English master hesitated a little taken aback, as I was not renowned for my comprehension of literature, and then said, "Very good" with heavy emphasis on "very."

I basked in that euphoric moment for about five seconds before my best mate said in a just audible murmur . "He looked it up in the dictionary." My glorious moment had passed. Some best mate!

Regards
Paul

Luke wrote: I'm about to make a case for a cabinet that's joined at upper and lower corners with dovetails. All of the dovetails will be covered with mouldings and not be seen. So the only consideration I have in laying out the dovetail profile is strength.

I've read, and to me it is intuitive, that the strongest dovetail joint has equal sized pins and tails. I haven't, however, ever read much commentary about the actual size of the dovetails.

Hi Luke

You're over thinking it. Just make the widths comfortable.



Regards from Perth

Derek

I would have thought strength being the criteria, the number of face grain glue joins, balanced against thickness of parts (not getting insanely small that is), would be the critical thing.

For strength i make simple box joints, 1/8 or 1/4 inch, and they are incredibly strong

Originally Posted by Luke Maddux

My tendency on these kind of long case joints is to go for something around an an inch or inch and a half (25-38mm) per tail, with even sized pins.

25 to 38mm is about what you see on the old stuff Luke , sometimes less than 25 . I reckon they didn't fluff about carefully dividing distances for marking out most of the time , but used their fingers to do the marking quickly . For years Ive been looking at this and I can be seen laying my fingers over a tail to check how well it matches My finger widths in three of the ways they can be laid out .
Wide spaced ones like the tails on a tool trunk can be three finger tips side by side. Drawer sides can be two fingers side by side, or two , index and middle, middle laid over index turned sideways. This gives me the widest at 52mm then 35mm then 25mm .
So when I'm laying out I just mark out each side a good looking distance in and finger space the middle out lightly , if it doesn't come out even enough I just go back and go across again and even it out .These are pin centers of course. When its good I use that side or what ever it is, top or Bottom of a box to mark out the other sides etc, of the same width .

Originally Posted by Luke Maddux

.....I'm about to make a case for a cabinet that's joined at upper and lower corners with dovetails. All of the dovetails will be covered with mouldings and not be seen. So the only consideration I have in laying out the dovetail profile is strength.....

Good Morning Luke

Dovetails sure can be pretty, but as yours will not be seen, why dovetails?

Now that glues are almost always stronger than the timber, finger joints are almost always stronger than dovetails, and a lot easier to cut.

But they ain't dovetails !


Fair Winds

Graeme

Originally Posted by GraemeCook

Dovetails sure can be pretty, but as yours will not be seen, why dovetails?

Now that glues are almost always stronger than the timber, finger joints are almost always stronger than dovetails, and a lot easier to cut.

maybe not easier to cut, if doing them by hand

Originally Posted by ian

maybe not easier to cut, if doing them by hand

That's why table saws and router tables were invented.


Graeme

Originally Posted by GraemeCook

......Now that glues are almost always stronger than the timber, finger joints are almost always stronger than dovetails, and a lot easier to cut......

Graeme, any of the "natural" glues that have been used for the last 10,000 years (or much, much longer!) are 'stronger' than the wood they join, provided they are made up properly & applied to well-fitted surfaces. And if longevity is your worry, there are plenty of joints made with animal protein glues several centuries ago that are still hanging on quite happily. However, that said, glues of all types can fail, for various reasons, regardless of whether they are the product of nature or mans' clever chemistry, so I for one just don't trust to glue alone unless there is no reasonable alternative.

Being a belts and braces type, I prefer to add a bit of extra help to any joint wherever I can. Dovetails are no harder to make than 'finger' joints (by hand, that is, different matter if you would rather burn 'lectrons), so why not utilise the advantage of a joint that locks itself in one direction, at least? On carcases, I not only glue the dovetails that join horizontal & vertical members, I skew-nail through every 2nd or 3rd tail so even if the glue fails, the joint won't.

I do feel a bit sorry for the person who might want to salvage the wood in a few years time, but blowed if I want to have to repair a piece I've made. Actually, I do need to do just that, dammit; a join in the side of a Blackwood desk I made for my son about 20 years ago has let go. It was glued with the latest & best of the man-made glues on the market at the time. Wish I'd used good old hide glue, which I'd temporarily given up for the convenience of stuff you just squeeze out of a plastic container. That glue let me down on a couple of pieces, so I stick with hot hide glue for anything I want to last, these days.

Cheers,

Originally Posted by GraemeCook

That's why table saws and router tables were invented.

take care there Graeme, when it comes to carcass joints, Luke is very much a hand tool guy.

Dominos anyone?