Laying out dovetails - rough guidelines ????

[Rob Matarazzo]

I'm working on a utilitarian project consisting of a wooden box with dividers that will be used to store various items in the back of my vehicle. The box will be dovetailed and constructed of pine boards 3/4" thick. The edges to be joined are about 13 1/2" long. I know it's not super critical, but I'm looking for some rules of thumb for determining the size and number of tails to be used. It should be based on structural strength more than on cosmetics.

[Zach Dillinger]

Equally sized pins and tails will give you the strongest possible joint. The actual size / number of the tails aren't critical as long as you are smart about it (don't do 30 pins /tails for that length, and don't do one really big one). Size the pins based on what chisels you have available.

[Rob Matarazzo]

Thanks. When you say "equally sized pins and tails", I assume you mean the wider end of the tails is the same size as the narrower end of the pins, right?

[Zach Dillinger]

Yes, that is exactly what I mean.

[Mike Henderson]

My own preference is for narrower pins than the tails - I just don't like the look of really big pins. As for laying them out, you can use a set of dividers to step off the pins and tails. I didn't invent this technique but you can see it in my tutorial here (http://www.mikes-woodwork.com/ThroughDovetails.htm). Look down a bit on the page until you see a set of dividers.

Mike

[Jim Koepke]

Here is a post on some dovetail cabinets made for my wife. As mentioned by Zach, for maximum strength make the pins and tail the same size. Sometimes things are not made for show.

http://www.sawmillcreek.org/showthread.php?135061-Cabinets-and-Dovetails

The marking stick was made with my 1/2" chisel in mind. Since there are a few chisels of that size in my shop, it can do all the work on this size dovetail.

If you want a little show on your case work, go to the end of the thread. There is are pictures and text about how one of my wife's cabinets was given a little decoration via a few "love tails."

jtk

[Jim Koepke]

Here is a good picture of some of my dovetails with pins & tails of equal size.

250546

They may not be the best when it comes to beauty but the strength is there.

jtk

[Charles Bjorgen]

I was at my local Woodcraft store yesterday shopping for a marking knife and saw a reference to "London style" dovetails on the packaging of one knife. I'm assuming this refers to those dovetails that have the very narrow pins which some here think are not as strong as those with equal spacing of tails and pins. I've noted that some here have cut the narrow pin style even for work bench construction. Not arguing the point. Just wondering how factual the strength issue is? I like the looks of the narrow pin style. Form over function?

I spent some time studying the links provided by Jim and Mike. Very useful. Learning to cut dovetails by hand is my project for the new year despite a shoulder injury that has been pretty limiting until the past week or so.

[Zach Dillinger]

No doubt that many (myself included) prefer narrower pins, a la London style. And I'm not aware of any actual studies done on the different styles of dovetails with regards to strength. But the idea of making each part of an assembly equally as strong as every other part to make the assembly as strong as possible is age old. Sure, wood resists cracking across the grain quite nicely but in pine, I could see those narrow little pins just powdering right off in something intended for a lifetime of service in the back of a truck. You want each individual part as strong as every other part, no more and no less.

For aesthetic purposes, narrow pins will look much better (to my eyes anyway), but it sounds like that isn't a concern here. For fine furniture, such as dovetailed drawers, where the assembly isn't subjected to harsh, racking stresses across the grain, a London dovetail is just fine. Here, not so much. Equally sized components, that's the ticket.

[Chris Griggs]

For aesthetic purposes, narrow pins will look much better (to my eyes anyway)...

But Zach!!!!! No one is every going to see your pins anyway, right???? That would require you to expose your endgrain! How vulgar:eek:!!! ;)

[Zach Dillinger]

For dovetailed drawers, I have no issue with exposed end grain when done properly (half blind), since you don't see it all that often :) And the London pattern will minimize the amount of exposed end grain anyway...

[Chris Griggs]

For dovetailed drawers, I have no issue with exposed end grain when done properly (half blind), since you don't see it all that often :) And the London pattern will minimize the amount of exposed end grain anyway...

Touche' :)

Yeah, I figured that's what you meant. I just couldn't resist, trying to give you some grief.

[Zach Dillinger]

Touche' :)

Yeah, I figured that's what you meant. I just couldn't resist, trying to give you some grief.

And i appreciate it. Keeps me on my toes. Can't be too complacent around here :)

[Mike Henderson]

Let me just add a comment about the width of pins - which may not be applicable to your project since it's basically utilitarian.

There are many jig/router combinations used today to make dovetails. But often, the craftsman (or craftswoman) wants to show others (perhaps other furniture makers) that the dovetails are hand cut and not made by machine. There are a few ways to do this.

1. One way is to make the pins small, with the narrow end smaller than the shaft of a router bit. When taken to extreme, the narrow end of the tail is only wide enough to get a saw into the cut between the tails. Warning: It's harder to chop out the waste in such spaces.

2. Most of us use a marking gauge to lay out the tails and pins. Many people make the marked line deep so that it survives the final sanding or scraping. Those lines are only used in hand cut dovetails so they're a sign that the dovetails are hand made.

3. Some people vary the angle of the tails slightly between tails. If you do hand cut dovetails, this happens almost without you trying unless you're very accurate in your sawing. But some people add the variation intentionally. If the area between the tails is cut with a router bit, the sides of the tails will be exactly the same angle.

There are probably other things that would tip someone off to hand cut dovetails but I can't think of them right now. Irregular spaced tails and pins are not a sign because high end jigs allow such spacing. Almost everyone will "mess up" the fit of at least one tail/pin combination so that's another sign, but not one that's desired.

But almost any way you make them, dovetails are very strong, usually much stronger than necessary for the joinery.

Mike

[Adam Cherubini]

To my thinking, equal strength would mean the narrow part of the tails would be similar to the narrow part of the pin (shear). If this were the case, the pin board would be a bit stronger (due to the taper of the pins). Therefore slightly smaller pins than tails would be closer to optimized for strength. And we see this on period work ish.

Perhaps more important than strength is maintenence of equal area of exposed end grain. Tho so many woodworkers (not us) assume wood is like aluminum and can be machined to aerospace tolerances, we know wood changes size and does so principally thru the seasonal movement associated with the uptake of water vapor thru exposed end grain. And that movement is localized to the ends of boards.

With this in mind, you could attempt to equalize exposed end grain. The finished joint would have the tails spaced slightly wider apart. An exact recipe isn't possible without fixing the angle. And I doubt any craftsmen would both to maintain such a formula. But you sure as heck could eye ball it. Whatever chisel was used to chop the tail waste would be just a tad larger than the wide part of the tail. (Can you tell I'm a tails first guy?)

The tiny pins we associate with London furniture are nearly always associated with half blind dovetails on drawers. Tho we may not know the original builders' intentions, we do know that the use of tiny pins reduces the area of exposed end grain of the drawer fronts. This is critical to the maintaining of flat, uncracked drawers. On these very same drawers, the joints at the back of the drawer almost never feature the tiny pins (see blow for more info). Nor are the tiny pins typically used in the carcase dts. This suggests to me London craftsmen were specifically attempting to protect exposed endgrain of drawer front, which were a problem (especially when veneered) during the 18th c. Interestingly, cockbeading had a similar effect.

Also, I typically see one fewer pin or tail on the back joints than the front. Was this done to resist with-the-grain cracks during assembly of the drawer? Certainly has that effect. One fat pin in the same spot on the front and back joints could crack the whole side.

If you ask an art historian, their answer is that these features are purely esthetic. No answer for why then are other exposed dovetails not handled this same way. That's when I usually get the standard museum answer (which I hate) "it varied", or (as if they have any idea) "it was standard shop practice".

I'm not convinced every 18th c craftsman was an expert in strength of materials, botany, and organic chemistry. We do know they were repairing their own and others' work fairly regularly. My guess is they adopted practices to reduce repairs. As firms grew so large that they lost contact with their customers (delivering furniture by rail for example), sometimes the practices lived on without the original understanding (reference the sawing off the ham story).

[Sean Hughto]

Don't stress about this much as dovetails are an extremely strong joint. From an engineering sort of perspective you have lots of slack to achieve all the necessary load tolerance you could need. In other words while 12 tails might be stronger than 6 across that 13 inches, 6 is stronger than you're ever gonna really test or need. Same for tail to pin size ratios, at least as long as you don't make needle thin pins. Just make something that looks good to your eye, and the strength will not be a worry.

[Trevor Walsh]

My own preference is for narrower pins than the tails - I just don't like the look of really big pins. As for laying them out, you can use a set of dividers to step off the pins and tails. I didn't invent this technique but you can see it in my tutorial here (http://www.mikes-woodwork.com/ThroughDovetails.htm). Look down a bit on the page until you see a set of dividers.

Mike

+1 I use the same technique. It's simple and easy. Some work needs a very thought out layout, say for a box that is to be assembled and then lid sawn off so you need a wide tail to account for the kerf and look correct after.

[Jim Koepke]

Some work needs a very thought out layout, say for a box that is to be assembled and then lid sawn off so you need a wide tail to account for the kerf and look correct after.

Careful now, this may lead to a controversy as to whether the end should be a tail or pin.

That would surely lead to pins or tails first shoot out.

Once that gets heated up we can only expect the thread to be closed by one of the moderators.

In my opinion, they all serve their purpose.

One planing point to take into consideration is what tools one has to achieve the objective. It is hard to clear a 1/4" of waste between tails if all you have is a 1/2" chisel.

jtk

[Jim Neeley]

Just my $0.02..

Dovetails were originally utilized to provide mechanical strength before gluing technology reached where it has today. Today's glues, properly applied (long-grain to long-grain and tight joints) are typically stronger than the wood itself.

The comments above about "sizing for maximum strength" are correct. The comments above about sizing for appearance are also correct. How can this be?

I've seen demonstrated a "london-style" half-blind dovetailed joint (two boards ony, one 3/4" walnut [pins], one 1/2" aspen [tails]) 3 tails well cut and glued together with titebone III, set in "tee-pee" form on a slick linoleum floor and with a 200# man bouncing on top of it and there waqs no failure.

Would it be weaker if there were gaps in the joint? Yes. Would it be stronger if all pins/tails were the same size? Perhaps. Do you need it stronger than that? That's for you decide based upon the application.

Theoretical or analytical arguments aside, many folks have very good results with think pins and so use they for appearance. Again, your choice.

Just my $0.02.. YMMV.

Greetings from Alaska

Jim

[Rob Matarazzo]

Thanks all for the useful information. For the record, I chose 5 tails, with the wide dimension of the tails the same size as the narrow dimension of the pins.

[Leo Passant]

Adam Cherubini (post #15) hit the nail on the head regarding 'London" lapped dovetails. If you have ever seen early, non-'London' drawers, the top edge of the drawer is often lower in height than the outer ends. The ends may also show signs of rubbing the top of the drawer aperture. The reason for wider tails and sockets was to reduce the amount of exposed end grain on the drawer front, thus lessening the chance of the ends taking up moisture and expanding. Over many decades, the width of tails and sockets increased in proportion to the drawer height until a balance was reached between end grain exposure and strength.

If anyone has any reservations as to the strength of (well made) 'London" 'tails, ask yourself how thousands upon thousands of extant examples have survived to this day... and then take one of the drawers and try and knock it apart with a deadblow mallet!


Dovetails were originally utilized to provide mechanical strength before gluing technology reached where it has today.
Glue technology was sufficiently advanced centuries before dovetails were generally employed for drawers and carcases.

[Don Dorn]

I too like the look of London style pins but use them only on something that is meant to be decorative. For drawers, smaller carcasses and so on, I revert to the way I learned which is the Frank Klausz method. No layout, just division by eye. To my eye, too much layout begins to resemble machine cut dovetails which is what I strived to get away from when I learned. To each their own, but for me, I'd rather have the layout look less than perfect, but produce a strong joint with pin sizes dependent on the width of the piece.

Klausz wrote an article once in regard to the craftsman to constructed the coffin the Pope was buried in. It had very wide pins and tails but it looked right for the size. I remember looking at online and can see his point - smaller would have looked to busy and too wide would have resembled a large box joint. It's interesting to read all these points of view.

[Mike Henderson]

Glue technology was sufficiently advanced centuries before dovetails were generally employed for drawers and carcasses.
That may be true, but if you think about how drawers are constrained from the sides and the fact that tails are put on the sides of the drawers, drawers could be built without glue and they'd work just fine.

Also, dovetails go back thousands of years - maybe not for drawers, but certainly for other pieces of furniture. Furniture with dovetails were discovered in Egyptian tombs.

Mike

[Jim Foster]

I've read about dovetails for many years, (not made many yet! :) ) and never seen anything written about this type of dovetail that offered any potential explanation beyond esthetic and guys showing off their skills. Very interesting!



The tiny pins we associate with London furniture are nearly always associated with half blind dovetails on drawers. Tho we may not know the original builders' intentions, we do know that the use of tiny pins reduces the area of exposed end grain of the drawer fronts. This is critical to the maintaining of flat, uncracked drawers. On these very same drawers, the joints at the back of the drawer almost never feature the tiny pins (see blow for more info). Nor are the tiny pins typically used in the carcase dts. This suggests to me London craftsmen were specifically attempting to protect exposed endgrain of drawer front, which were a problem (especially when veneered) during the 18th c. Interestingly, cockbeading had a similar effect.

Also, I typically see one fewer pin or tail on the back joints than the front. Was this done to resist with-the-grain cracks during assembly of the drawer? Certainly has that effect. One fat pin in the same spot on the front and back joints could crack the whole side.

[James Mittlefehldt]

Hi all I have not been around much until just recently and am pleased that there are still discussions going on about dovetails and workbenches.

In answer to someones wondering about testing the relative strength of dovetails I believe, if memory serves, FW did a test once upon a time where they tested the relative strength of various woodworking joints. In that test they did try out small pin or London pattern with equally spaced and found that yes indeed the equally spaced worked best for maximum strength. HOWEVER they also qualified the results by saying that while the small pin dovetails gave way sooner that point was still well beyond the stress that most of them would ever be subjected to in normal usage.

Also I would point out that I have looked at many pieces of furniture over the years and many pine cupboards I have seen had dovetails that looked like they were made more by a carpenter or joiner as opposed to a cabinet maker, and while the furniture was usually well over a century old the rough looking dovetails were still holding up.