Through Dovetail Tails First

Dovetails are cut by superimposition. I wrote earlier about laying out mortise and tenon joints by superimposing one element on the other and transferring dimensions. This makes some people uncomfortable. Good cogs in the mass production machine are supposed to work from a measured drawing, manufacturing each precise part and then fitting them all together. But try to find a measured drawing from the days of the great cabinetmakers—there are none. Their forms emerged from the constraints of classical proportion, customer demand, and mechanical necessity. They built furniture largely with superimposition shaping each piece of the emerging whole.

The immediate question for dovetails is, which do you cut first? Which part gets to be the super of the superimposition, the tails or the pins? In secret miter dovetails, we have to cut the pins first, so that's settled. But we're making through dovetails now, so we'll do them tails-first.

The wide boards of this chest will have lifting handles on the end. Thus, the tails will go on the sides and the ends will get the pins. Dovetailing can be no more precise than the boards are square and true. Square all the end grain with a block plane, leaving it smooth to allow clear marking.

Assuming you are joining equally thick boards, set the gauge 1/32 inch greater than the thickness of the boards and run the fence of the gauge against the end grain of each of the boards to mark the extent of the tails and pins. This extra 1/32 inch gives you something to plane off the completed joint. Lightly trail the point of the gauge across the grain rather than scratching and tearing. A lightly held cutting gauge serves even better.

Now decide the spacing of the tails and pins. If the chest has any skirting around the base or lips to meet the lid, consider their locations so the dovetails won't begin or end awkwardly. If the boards will have a groove plowed down their inside to hold a bottom, that groove should not overlap the joint between a tail and pin. Make these grooves first so they won't be a surprise later on.

To fight confusion, I'll call the piece with the tails the tail board, and the one with the pins the pin board.

We will cut the tails first, meaning we are working on the broad sides of the chest and defining the sockets for the pins between the tails, the pin spaces. Custom demands that dovetails end on a half-pin, although you may find otherwise in old pieces.

The size of the pins relative to the tails is an aesthetic/mechanical tradeoff. For a heavy chest, you could make them equal in size, but even when equal spacing would be stronger, a chest looks far better when the pins are about half as wide as the boards are thick, and the tails are about three times as wide as the pins.

By this guideline, the thickness of the wood determines how many tails and pins will fit within a given width. For 3/4-inch-thick, 11-inch-wide boards, this comes to 8 dovetails separated by 7 pins, bounded by a half-pin on each end. We thus need to divide the 11-inch board into 8 equal spaces—not measuring from edge to edge, but from the centerline of one outer half-pin to the centerline of the other.

At their widest points, these half-pins should be the same width as the full pins, at least half the thickness of the wood, in this case, 3/8 inch. This puts their centerlines at 3/16 inch back from the edges. (If you think the corners are going to take a beating, you can make the bounding half-pins a bit wider.)

Back to dividing an 11-inch board into 8 equal spaces. Hold a ruler diagonally on the board with the zero end crossing the centerline of one half-pin and the 12 crossing the centerline of the other. Put a pencil mark every 1 1/2 inches down the diagonal ruler. Carry these marks up to the end using a try square and a pencil, dividing the width into 8 equal parts.

This works for any width or number of divisions. You would place a mark every 2 inches if you wanted to divide the board into 6 equal parts. For 7 equal parts, position the ruler at zero and 14 and mark every 2 inches. For 5, go to 15 and mark every 3.

Anyway, where each pencil line crosses the line marked by the gauge, measure out the width of the pin space, 3/16 inch on either side for a total of 3/8 inch. This is the widest part of the pin space, the narrowest part of the dovetail, and the slope starts here.

Gauge each piece to its mate's thickness, plus 1/32 inch.
Divide the width into equal parts using a diagonal ruler.
Lay out the spaces between the dovetails.

left: Chisel down from one side... right: . . . and completefrom the other.

For most work, find the slope angle for your dovetails by setting the sliding bevel to cross the one and the six inches on the square. A one-in-five slope looks more robust; a one-in-seven looks more delicate.

Whatever angle you decide upon, set the beam of the sliding bevel on the end grain and draw the converging sides of the pin spaces up from the gauged line with a sharp pencil. Mark the little spaces with Xs so you will know what you will be cutting away. Carry all these lines square across the end grain and use the bevel again on the back side. The lines across the end grain are the most important. You can have variation in the slopes between different dovetails —they'll just look funky. But if the lines aren't sawn square across the end grain, the assembled joint will have gaps that weaken the whole works.

Sawing at last. A dovetail saw is simply a fine-toothed backsaw, but use what you have. Saw precisely parallel to the lines, touching them but leaving them intact. Saw diagonally at first and watch that you leave the line on both faces.

The ends where the half-pins fit will come off with two more cuts from the saw, but the rest of the pin spaces need chisel work. You could remove most of the wood with a coping saw or, in heavy work, use an auger, but normally this is all push chisel work. If the pin spaces are 3/8 inch wide at their base and taper down from that, the largest chisel you can use is one about 5/16 inch wide and beveled on the sides because you must start a bit clear of the scribed line.

Try working with two chisels, starting by pushing straight down with the wider chisel, flat face to the line. Then, with the narrower chisel held bevel down, push toward the bottom of the first cut and remove a chip. Working down, excavate halfway through. Flip the board over and make the same V-opening to meet the first one. Leave the narrow end intact to support the waste until the V-cuts meet — otherwise it might break out and tear the wood. Clean up and trim the pin sockets back to the line.

Now we'll cut the pins to fit into these sockets.

See that the board for the pins is not cupped, clamping a batten onto it if necessary to hold it flat. Set it in the vise as you hold the end grain flush with

left: Set the tails on the joining board and mark the pins.

right: Cut the sides of the pins with a dovetail saw, and remove the waste with a coping saw.

left: Set the tails on the joining board and mark the pins.

right: Cut the sides of the pins with a dovetail saw, and remove the waste with a coping saw.

a piece of scrap or a plane lying on its side. Push this scrap or plane back across the bench to support the back end of the tail board, the super board of the upcoming superimposition.

Align the board bearing the tails on the end of the pin board. See that you are well and truly aligned to the scribed line with the extra 1/32 inch hanging over. A pencil can't reach into the tiny pin spaces, so scribe the width of the openings onto the end grain of the pin board with a knife, cutting dead flush to the walls of the sockets. Don't let the board move until they are all marked.

Remove the tail board and elevate the pin board enough that you can carry the lines square down to the depth mark with the try square. Mark the waste pieces with penciled Xs. You are now about to remove big pieces and leave small ones. Accurate sawing on the waste sides of these lines will make the joint fit without trimming. Split the lines with the edge of your saw kerf, and the whole should fit up fine.

The waste from the broad sockets for the dovetails is large enough to make the rough cut with a coping saw worthwhile. Work from the face side with the teeth cutting on the pull stroke. It may be that your coping saw cuts a wider kerf than the dovetail saw, so keep it pulled to the waste side as you work your way down to make the turn across the grain.

The broad bottoms of these sockets for the tails form visible parts of the joint and need to be straight and clean. Lay the piece on a scrap block on the bench and pare toward the middle with the freshly sharpened chisel set right in the depth line for the final cut. Finally, you stand the piece up in the vise again and shave with a diagonal shearing cut of the chisel to smooth the bottom.

Test the fit. Don't bevel the ends of the pins to make the fit easier—you've got only 1/32 inch to play with. Instead, pare back the hidden, inside corners of the dovetails. This beveling strengthens the edges of the tails and gives a little clearance for any stuff in the corners. Watch for a fat fit that could cause a split, particularly against the half-pins at the ends. Use a cabinet file to trim if you need to, but mind its corners.

Set a batten across all the tails to spread the impact and protect the tails as you drive them up with the mallet. You may want to use bar clamps to draw the joint up instead. First time out, bring the joint all the way closed before tapping it apart, applying glue and re-closing and squaring it. With more experience you can just make a partial test fit before gluing. After the chest is joined and

Chisel flush to the gauged lines.
Bevel the inside corners of the dovetails.
Tap the joint closed.
"Kerfing in" a box made with mitered corner dovetails.

the glue fully set, trim the protruding ends of the tails and pins with a block plane, working from the outside in so you don't splinter off any ends.

Through dovetails in plain flat boards are the simplest expression of the joint. In practice, there are complications.

If you have a groove on the inside of the chest, you must leave an extra shoulder at the bottom of the dovetail socket to fill the wood removed by that groove. This makes a shallower, slightly weaker and odd-looking joint. You may be better off stopping your grooves short of the ends of the chest so the dovetails can remain whole. If you have a rabbet running around the inside of the rim of the chest, leave an extension of the dovetailed piece to fill the gap in the half-pin.

You can also deal with a rabbet by cutting a plain, butted miter into the halfpin of the dovetailed joint. This miter allows you to cut uninterrupted exterior moldings as well. Your brain has to change gears to do this, from square cuts to diagonal. Cut the miter a little fat and then kerf it in by repeatedly sawing the crack and tapping it together until the dovetails close.

Woodworking Tools and Installation Tips

Woodworking Tools and Installation Tips

There are a lot of things that either needs to be repaired, or put together when youre a homeowner. If youre a new homeowner, and have just gotten out of apartment style living, you might want to take this list with you to the hardware store. From remolding jobs to putting together furniture you can use these 5 power tools to get your stuff together. Dont forget too that youll need a few extra tools for other jobs around the house.

Get My Free Ebook

Post a comment