Dovetails - Part 3 of Wedding Present
The dovetails
This is part 3 of a series of articles based on the construction of The Wedding Present. If you’re only interested in my dovetail methods, just read this. If you are interested in the context of the dovetails, start here.
As it’s a while since I hand-cut dovetails I did a little practice work. (I’m a traditionalist and cut the pins first and mark the tails from the pins.)
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| Pins: Pins cut in test piece | Tails: Cut from the pins |
Tools
This lead to a re-examination of my tools. My dovetail marking guide is homemade from a piece of 1½” brass angle. While it has served me well for many years it has some drawbacks including not being as symmetical as I’d like. While searching for a replacement I came across the tools of Chris Vesper.
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| Old: Old dovetail guide made from brass angle. | New: Chris Vesper’s dovetail guide. |
I bought his dovetail guide and found it handles very well. The extension of the reference bar on each side of the guide makes the marking of pins near to the edge of the piece much easier than with my angle guide. (The red ‘X’ on the 1:6 guide is just to remind me that I should be using 1:8 in case I accidentally turn the guide around.)
Another acquistion: Chris Vesper’s ‘double square’
While I was at Chris’ site I picked up his marking knife (I’d also been just managing with a sharpened length of 1″ hacksaw blade for 15 years - still useful for some applications) and his ‘double square’. The latter is a small square that has a movable blade like a traditional large combination square. As well as being a beautifully finished tool that is a pleasure to use, the adjustable blade has proved its worth many times in the short while I’ve used it. Woodworkers will know the annoyance of putting a narrow board into their vise for edge-planing and then reaching for their 2″ square only to find that the edge of the board is just less that 2″ above the jaws. Rather than reposition the board in the vise so that the square fits, you can just shorten the blade of Chris’ double square to check your edge. The narrow blade shown in the photo interchanges with the larger blade. It is extremely useful for checking squareness in tight confines. This is exactly what you need when checking the squareness of your tails if you cut very narrow pins as I do.
I’ve never been quite happy with my Pax dovetail saw - mostly from its lack of balance in the hand. I was happy to discover on Chris Vesper’s site a maker of dovetail saws in Canada - Adria Saws.
Having received all my new tools I could no longer put off cutting into these beautiful pieces of wood.
Over or under?
The first decision in cutting dovetails is whether you mark up so that the pins and tails protrude slightly beyond the outside face of the joining piece or stop slightly short of the face. By far the most common practice is to allow the pins/tails to protrude by 1/3 to 1/2 of a millimeter. This makes planing the outsides flush very easy because you only need to remove the excess from the pins/tails rather than planing down the entire side. However it does mean that cramp-up is more complex because you cannot just cramp against the face but have to make a cramping block that will allow the protruding pins/tails to . well .. protrude.
My teacher, George Ingham of the respect for tradition school, always insisted on leaving the pins/tails just short of the face. After all if you can’t competently plane the face of your wood, what are you doing cutting dovetails! I’ve always been somewhat agnostic about this and tend to use the method that suits the project. I have also had a bet each way and let the pins protrude (because the cramping block for this side has plenty of leeway and lots of area to push against, and cut the tails just shy of the face because when you use narrow pins there is very little surface to cramp against. I also make the difference very small (like about 1/6mm) so that it is easy to clean up either way. The difficult grain in the pieces I was using meant that I didn’t really relish planing too much off the faces.
In this case I have chosen to cut the pins on the shorter side pieces so that the front elevation of the box shows only the narrow ends of the pins. The blockier tails show on the sides. When you use dovetail joints on drawers, the orientation is all important and the tails must go on the sides so that the inherent strength of the joint is used to resist the force of the drawer being pulled from the front. As there is no directional bias of forces on a box the choice can be based on asthetics alone. In this case I wanted the front to be uncluttered.
Cutting the pins
I mark the width of the joining pieces (+ or - 1/6mm) on the inside face of the pin pieces with a knife. The mark is transferred to the outside across the bottom of the piece (the small knife mark will be planed out when the base of the box is flattened. I use a fine pencil line on the outside as a guide until the pins are marked.
I lay out the pins on the end of the pieces using a dovetail guide and then extend the marks square to the end until they meet the knife mark on the inside and the pencil line on the outside. Once the narrow edge of the pins are marked on the outside face, the pencil line is replaced by a knife mark in the waste areas only.
Dovetails: Pins are cut and pared
The faces of the pins are then sawn and the waste removed with a coping saw. The base of the waste area is pared flat and square to the faces. I don’t believe in undercutting these surfaces in order to obtain a better final appearance (at least not deliberately!). If I learned anything from George Ingham it was to respect the integrity of the joint. This relates not only to the structural strength of the joint but also to the very reason we choose to hand-cut dovetails in the first place.
Marking the tails
The traditional rationale for cutting the pins first and then marking the tails from the pins is that the tails are marked onto the face of the tail piece. If you do it the other way around you have to mark the pins onto the end-grain of the pin piece. End grain is generally less able to sustain a clear marking line than face grain. This argument applies more to the softer woods used in traditional European furniture than it does to the hard Australian woods which can usually carry a fine line in their end-grain. Nevertheless I have always had better results cutting the pins first so I tend to stick with this approach.
Dovetails: Setup for marking the tails from the pins. The tail piece is held steady by a bench clamp (out of shot). The block to the left aligns the reference edges of the two pieces.
When marking the tails from the pins, it is always worthwhile spending a little extra time creating a stable and well lit arrangement. Trying to steady two pieces of wood and mark at the same time when shadows are working against you is a recipe for error. My setup for this job is shown in the picture above. The block on the left-hand side aligns the two pieces on their reference edges. A waste piece (with a very square end) is positioned on top of the tail piece so that its end aligns with the knife mark on the inside. Both pieces are held in place with a bench cramp.
Dovetails: The tails have been marked from the pins
Three possible marking tools are shown - a pencil, a scribe and a knife (No. 11 scalpel blade in this case). I favour (and used in this case) the scalpel blade as it can make very clean marks, has good access to the tight spaces and doesn’t restrict vision too much. As it is double-beveled you need to be careful to maintain a angle that makes sure the cutting edge is hard against the pin while still making an essentially vertical cut into the piece. A fine single-bevel, pointed marking knife would be ideal here but I’ve not yet found one. The resultant marks are shown in the photo.
Cutting the tails
Dovetails: The tails are cut from the marks on the inside face
The tail markings are squared across the end of the tail pieces. The marked lines are then sawn down to the width of the pin piece. It is inherent in the geometry of constructing a dovetail joint that the transfer of the shape of the pins is to the inside face of the tail piece. This means that the tails must be sawn absolutely square to the face because it is the fit of the pins to the outside of the tail piece that we actually see.
Paring the tails
Dovetails: Paring the tails
The waste between the tails is removed (in this case with a jeweller’s saw because of the small space). The base of waste area is then pared. Placing a light source directly behind the cutouts can help with paring a flat base to the narrow space. The following picture shows a pared shoulder. You can see the knife cuts around the edges extending about 1/3mm into the wood. These marks are used to pare the rest of the shoulder flat.
Dovetails: Paring the shoulders
Fitting
Each joint is then tested for fit and tuned if required. These are some shots of the cut joints assembled dry.
Dry assembly: The slight protrusion of pins and tails can be seen
Dry assembly: A completed joint ready for glue-up
Pre Glue-up
There are a few things to be done before glueup - like fitting the bottom panel, the runners and the magic catch. These are described in the following posts. However there are also some tasks specific to the dovetails that I will describe here.
The inside surfaces of the four sides must be fully sanded as it is impossible to sand these surfaces well after the box is assembled.
And you need to choose a method for cleaning up the excess glue on the inside of the joint. There are several ways to do this including washing the excess glue away with water and a toothbrush after cramp-up but before the glue goes off. I usually have too much to do in the short time available during glueup so I prefer to use the following method.
Find a thin sticky tape that you are sure will peel off the wood without leaving any gum residue. It needs to be thin so you can get the edges right into the inside corners of the glueup. I used to use a brown packing tape that was ideal because it was very thin and very waterproof. The latter means that the excess glue will not even stick to the tape and is very easy to remove. Unfortunately all the packing tape I have bought in recent years leaves lots of residue when you peel it off. This is as hard to remove as the glue. I now use a blue masking tape made for painters. It is slightly thinner than ordinary masking tape and is easy to remove.
Pre-glueup: Inside of joint taped to handle excess glue
The plan is that you apply the tape to the inside faces (the ones that are hard to clean up after glueup), making sure you place the edge of the tape exactly on the intersection of the joint. The excess glue will flow out on top of the tape and harden there. After the glue is dry, you can just peel off the tape and remove most of the glue. Any remaining glue is usually a fine sliver which can be removed with a marking knife. The intention of all this is to prevent the excess glue soaking into the wood and marring the appearance of the piece after the finish is applied. (I don’t have an image of the box sides with tape applied but the accompanying image shows the same technique used on the box lid.)
Glue-up
I use a yellow PVA glue for glueups like this where high strength, longevity and minimal glueline are the main criteria. In this project I used Titebond’s PVA for the first time.
Glueup: The dry run for gluing the front-left corner
The first two joints are glued in separate sessions so that I have the maximum time to attend to each joint. (The time from starting to apply the glue to having the joint in the cramps under pressure should be less than two minutes - then you have a few minutes to check and adjust squareness.)
Glueup: The last two joints (the two at the front of the bench) are glued at the same time.
The remaining two joints have to be glued in the same session (dictated by the geometry of dovetails and most other joints).
It is essential to do a dry run for each glueup session to make sure everything fits and that all the cramps and cramping blocks are adjusted and ready to go.
Part 1 The present
Part 2 The wood
Part 4 The lid
Add comment July 13th, 2007
