Dovetails are prime joints. They are strong, have a long history of use and great appearance, are strong, and have cachet. Dovetails are used in boxes, drawers, carcasses. Oh, and did I mention that dovetails are strong?
But for many woodworkers, cutting dovetails the traditional way -- with saw and chisels -- is an insurmountable challenge.
If you are in that group, there are plenty of router accessories on the market to help you. There are so many, in fact, and they have so many variations in setup and operation, that I'm going to narrow my focus to the most common: the half-blind dovetail jig.
The typical half-blind dovetail jig consists of a metal base with two clamping bars to hold the workpieces. A comb-like template rests on the top to guide the router in cutting both pieces at once.
|
The half-blind dovetail jig cuts pins and tails at the same time with the same bit. This model has a rigid extruded aluminum base and a durable phenolic template. Its large knobs are easier on the hands during extended dovetailing sessions than the wing nuts found on cheap jigs. The jig is mounted on a shop-made platform that expands workpiece support and incorporates positioning fences on the front and the top.
|
The biggest differences from brand to brand and model to model are the quality of the materials and hardware, as well as the precision with which the jig is made and assembled. The cheap ones have flimsy stamped parts, threads that strip, wing nuts that chew at your fingers. The model shown in the photos has a rigid extruded aluminum base and a durable phenolic template. Its large clamp knobs are easy on the hands during extended dovetailing sessions. Some jigs have an extra template for 1/4" half-blind dovetails, and a few have them for 1/4" and 1/2" box joints as well.
Besides the jig, you need a router, a 1/2" 14° dovetail bit, and a guide bushing. Usually a 7/16" O.D. bushing is required, though occasionally a larger bushing is called for. The appropriate bit and guide are typically packaged with the jig, and in most instances, you'll find they are generic. Because the working end of the bit is larger than the opening in the template guide, you have to install it after the template guide. That means there's benefit in using a long-shanked bit, though that's not what is packaged with the jig typically.
 |
| A 1/2" dovetail bit doesn't fit through a 7/16" template guide. Most guides are steel, which will damage the bit's carbide, so you must install and adjust the bit with care. |
You can use any router. I've routed dovetails with a laminate trimmer, but typically use a 1-1/2- to 2-horsepower fixed-base model. The ability to plunge is irrelevant in this operation, and plunge routers generally are awkward for work on the edge (which this work is) owing to their high centers of gravity. Brute power doesn't contribute much, if anything. But don't go buy a new router just for dovetailing.
Setting Up Your Jig
Every half-blind dovetail jig I've ever seen needed to be attached to a base (something like a piece of 3/4" plywood), which could then be clamped to a workbench.
If you are expecting to use your dovetail jig a lot -- you've got dozens and dozens of drawers on your To Do list -- it's worthwhile to spend a little more time and build a platform for the jig (see the Drawing). The platform expands the surfaces that support the pieces you are dovetailing, and adds fences to supplement the alignment pins on the jig.
The payoff is that you'll be able to align the pieces in the jig more
accurately and with less fussing. You'll save time, and probably will
waste less material.
|
While details may be different, the dovetail jig shown here is typical of half-blind jigs. The foundation is a rigid stamped or extruded metal chassis with three pairs of studs for mounting two clamping bars and the template. It also has two pairs of guide pins or bars.
The guide pins -- a pair on the left and a pair on the right -- locate the workpieces, so the tailboard is offset 7/16" from the socketboard. The clamping bar that holds the socket-board mounts on a pair of studs on top of the chassis. A duplicate bar for holding the tailboards mounts on studs on the front of the chassis. A second pair of studs on the chassis front support the template.
If the jig takes more than one template -- say, a 1/4" template as well as the standard 1/2" one -- the guide pins will be adjustable, so you can set the proper offset for the chosen joint.
The clamping bars are secured with wingnuts or knobs. Large knobs or plastic wingnuts are far easier on your fingers than metal wingnuts. Don't minimize the significance of this.
At minimum, you should mount the jig on an oversize board that you can clamp to a workbench. But a modest additional investment of materials and jig-building time can pay dividends in the long run. Add expanded support surfaces for both the tail- and socketboards, and equip them with fences to positively align the boards.
|
|
Stock thickness doesn't affect router-cut half-blind dovetails. You can use one thickness for the socketboard, a different thickness for the tailboard. Shown here (top to bottom) are a 3/4" tailboard joined to 7/8" socketboard; 1/2" joined to 3/4"; 1/2" plywood joined to 3/4"; and 3/8" joined to 1/2". Only if you vary the thickness of the tailboards during a joint cutting session do you have to alter the jig setup.
|
Routing Dovetails
When the urge to rout dovetails seizes you, get out your jig and clamp it at the edge of your workbench. Presumably, you'll have stored the manual or instruction sheet and the appropriate bit and template guide with the jig.
Select your materials and make sure all like parts are jointed and planed uniformly. Not all the parts must be the same thickness. The fronts can be 3/4" thick, and the sides and backs 1/2", for example. Or 3/4" and 5/8". Everything can be 11/16". Just be certain the fronts are consistently sized, the sides are consistently sized, and the backs are consistently sized, too.
|
For the sake of appearance (it won't affect the strength of the joint), you want to begin and end with a half pin. But routed half-blind dovetails are inflexible. The 1/2" dovetail lays out on 7/8" centers. That is, the distance from the center of one pin to the center of the next is 7/8". You can't alter their size to distribute them evenly. What you have to do is scale the height of your assemblies in increments of 7/8".
|
Set Up the Router
Get out your router and make sure it has the correct collet installed. You probably won't be using a 1/2"-shank bit for this work.
 |
| Install the guide bushing before the bit, and make sure it is tight. Adjust the router so the collet is close to — but not touching — the bushing. Insert the bit shank — you've got to use a 1/4"-shank bit — through the bushing and into the collet. You want to extend the shank well into the collet, yet allow leeway for cut depth adjustment. |
 |
| In setting the depth of cut, you must account for the template thickness as well as the cut itself. Use a small machinist's square, graduated in 64ths, to set the bit extension, measuring from the baseplate. Turn the bit slowly by hand to ensure the bit doesn't contact the guide. |
Install the guide bushing. Adjust the router so the collet is relatively close to the bushing. Carefully insert the dovetail bit through the bushing and into the collet. Tighten the collet nut.
Adjust the depth of cut next. When you do this, turn the bit slowly by hand to absolutely ensure that the bit doesn't contact the bushing. In most instances -- not all, but most -- the cutting end of the bit is too large to pass through the bushing. If you use a steel bushing, it will damage the bit's carbide, so you want to avoid contact.
Check your jig's instruction for the recommended depth-of-cut setting. It's often in the 21/32" to 23/32" range, depending upon the thickness of the template.
A good generic starting point is 3/8" plus the template thickness (to get an accurate measurement of the template, use dial calipers).
Clamp the Work in the Jig
The workpieces have to be clamped in the jig in a particular way. One board is clamped to the top of the jig, the other to the front.
When you cut following the template, tails are formed on the front board, and sockets for the tails are cut into the top board.
So the socket piece -- and that's always the drawer front or back -- is on top. The tail piece -- the drawer side -- is at the front.
The alignment of the pieces is critical: The tail board overlaps the end of the socket board. The tail board's end must be flush with the upper face of the socket board. The boards must be perpendicular to each other.
In addition, the tail board is offset. Both boards are clamped in the jig with their "inside" faces out.
Here's the easiest way to do it. Roughly position the tail piece in the jig, with its top end well above the jig. Slip the socket piece under the top clamping bar, and butt it tightly against the tail piece. Clamp it firmly. Now loosen the clamp holding the tail piece and lower it until its end is flush with the other workpiece. Clamp it firmly.
 |
 |
| Line up the workpieces carefully as you clamp them in the jig. The
socket piece (a drawer's front, for example) lies facedown on top of
the jig. The tail piece (the drawer side) is held against the front of
the jig, and it overlaps the end of the socket piece. Its outer face is
against the jig. |
Make sure the pieces are aligned tight against the pins. The socket piece's end must be square and tight against the tail piece, and the end of the tail piece must be flush with the surface of the socket piece. Tighten the clamp bars so the pieces can't move. |
Both pieces need to be against the alignment pins or stops. These pins align the parts so they are offset exactly 7/16". (This is half the center-to-center spacing of standard router-cut half-blind dovetails [7/8"]. It's the distance the parts must be offset to produce a half-pin at the start of the joint and have the edges of the assembled joint be flush.) Every jig has these pins -- they're adjustable if your jig takes more than one template -- and it has a pair on the right and on the left. Use the pair on the left for now.
 |
 |
Both parts must be snug against the guide pins; this is where the
extra fences on a shop-made platform are beneficial. An accurate offset
between the parts is critical to having the edges of the assembled joint
be flush.
|
To balance the clamping pressure and to keep the template from
sagging, fit a spacer made with scraps of the working stock into the
unused side of the jig. I press together the pieces from test cuts, set
the resulting joint in the jig (which does require dismounting one of
the clamp bars), then slide it from side to side as I work the good
stock.
|
The fact that these critical alignment devices are pins and not elongated fences doesn't make it easy to align the work in the jig. The supplementary fences on the shop-made platform make up for this shortcoming.
 |
| On most jigs, the template is attached to a pair of L-shaped forked brackets. The forks drop onto studs projecting from the jig chassis. Make sure the template is seated flat on the work and that its back edge is parallel to the top clamp bar. Tighten the knobs or wingnuts to hold the template. |
 |
| Typically, the template brackets drop onto the studs in front of adjustment nuts. You turn the nuts to alter the fore-and-aft position of the template; this adjustment controls how deep the tails penetrate the sockets. Turn the nuts in to increase the socket depth, out to decrease it. |
Positioning the Template
The template rests on top of the work. It must set flat on the work. The fore-and-aft alignment is critical to the fit of the joint.
The most common mounting features an L-shaped bracket at each end of the template. The bracket extensions are slotted so they drop onto studs projecting from the jig chassis and can be secured with locking knobs. This holds the template so it doesn't shift as you rout.
To adjust the fore-and-aft position of the template, you turn a nut that's between the chassis and the template bracket on the stud. These studs usually are 1/4"-20 bolts, so a full turn of the nut will move the template in or out 50 thousandths of an inch.
The trick is ensuring that the template is parallel to the front edge of the jig. If it isn't, the sockets will be deeper at one end of the joint than at the other. That'll make you nuts! Don't fiddle with this adjustment yet. Use the out-of-the-box setting for your initial test cuts, then adjust as necessary.
Cut a Test Joint
This will be a test cut, but it sets the pattern for the production cuts that are to follow.
|
Chipping along the shoulder of the tail piece is a problem. As the bit exits a template slot, it pulls perpendicularly off the shoulder, lifting chips away from the surface. To eliminate the chipping, make a shallow scoring cut across the tail piece first thing. A climb cut — where you feed the router from right to left — is most effective here. Just be sure the router doesn't get away from you.
|
|
Routing the tails and sockets takes a matter of seconds. Move along the template, feeding the router into each slot and keeping the guide tight against the template as you come out of one slot and round the finger into the next slot. Any little bump on either tail or socket will prevent assembly of the joint.
|
|
Upon completing the cut, pop off the template and take a good look at the cut. If you see a little bump on a tail, or that you failed to get a socket cut to the full depth, you can usually replace the template and recut those spots.
|
Rest the router on the template, with its bit clear of the work. Switch on the router, and make a quick, shallow scoring cut across the tail piece, feeding from right to left (yes, this is a climb cut).
The purpose of this cut is to prevent tearout along what will be the inside shoulder. What often happens is that the bit blows out splinters as it emerges from each slot of the template. If there's not a shoulder yet, these splinters can run down the face of the drawer side, defacing it.
Now rout the dovetails, slot by slot, beginning on the left and working to the right. Feed the router into each slot of the template, then back it out. Keep the router firmly against the template as you round the tip of each template finger; you want to completely form each tail — no little lumps.
I usually zip back through the slots after the first pass, just to be sure I didn't pull out of a slot too soon, leaving that socket only partially cut.
Don't just lift the router from the template. The bit will ruin both the cut and the template. Instead, turn off the power and pull the router toward you, getting it well clear of the jig before lifting it.
Take a good look at the work and be sure you haven't missed a spot. (If you have, re-rout it now, before moving anything.) Only then should you remove the template, unclamp the work, and test assemble the joint.
Fine-Tune the Setup
Chances are, your setup needs a little fine-tuning. You slip the two test pieces together, and something's not quite right. Perhaps the fit is too loose. Or too tight. Or the sockets aren't deep enough. Or the parts are a little offset. All of these ills are cured with some fine-tuning.
The bit's cut depth is the primary control on fit. If the cut depth is wrong, either the tails won't fit into the sockets at all, or they'll rattle around in them. The way it works is shown in the Drawing, "Setting Depth of Cut." The cut -- the socket -- is always the size of the cutter. But when you alter the depth of the cut, the width of the material left between sockets changes. Because you are cutting both tails and sockets at the same time, the "material between the sockets" is in fact the tail.
In practice, this aspect of the setup is at the same time deceptive and frustrating. The transition from no fit to perfect fit is abrupt -- just a 1/32" change can make all the difference. What often happens is that you lose confidence in the adjustment regimen after three or four incremental changes with no apparent effect. "Well, this isn't getting me anywhere!" you think, and start adjusting in the other direction. And you seesaw between increasing and decreasing the cut depth, never hit the right setting, get totally frustrated, and shelve the %#$@*& jig, never to use it again.
This is where a router with precise controls is essential. Your initial setting may well have been measured in 32nds. Any adjustment changes both the tail and the socket. An adjustment of 1/64" might be just what you need. Can you make an adjustment that fine with your router?
Take heart. Remember that woodworkers have been using these jigs for decades, and that routers have been pretty primitive tools for most of that time. You can do it. Be patient, methodical, and persistent. Here's what you do:
- Reduce the cut depth to loosen the fit.
- Increase the cut depth to tighten the fit.
Once the depth of cut is dead-on, you must adjust the template's fore-and-aft position. This controls the relationship of the faces. With the template perfectly positioned, half the cut is in the tailboard, half in the socketboard (a.k.a the pinboard). Consequently, the tail just fills the socket; the tailboard face is flush with the pinboard's end. Back the template up: the pin is short and the socket is long. Advance the template: the pin is long, the socket short.
Your jig's instruction sheet should explain exactly how to accomplish these adjustments on your jig. The most common method, as I mentioned, is to turn a nut that's behind the template mounting bracket on the mounting stud.
The top and bottom edges should be flush when the joint is assembled. If they aren't, you may not have had the workpieces snug against the alignment pins. Or the pins may be slightly misadjusted.
Any other problems you have will stem from misalignment of the workpieces in the jig. Make sure the top surface of the socket piece is flush with the top end of the tail piece, that they are at right angles to each other, that the template is square to the workpieces, and so forth.
|
 |
| When adjusting the socket depth, you theoretically want the surfaces to come flush when the joint is assembled. But as a practical matter, a perfect flush fit may be easier to achieve if you deliberately have one surface just proud of the other. If you've fitted a drawer front to its opening, for example, it's better to have the tail piece just proud of the socket piece (left). That way, a pass with the belt sander or hand plane will bring the joint flush, without changing the fit you've established. On the other hand, you can get that perfect flush fit with less sanding if the socket piece is proud (right).
|
When you've successfully fine-tuned the setup using the alignment pins on the left, cut a test joint using the right end of the jig. Do any additional tuning needed there.
Dovetailing the Good Wood
Before starting on the actual project parts, make sure you're organized. The parts are worked "inside out." Some are cut on the right side of the jig, others on the left. It's easy to get mixed up, whether you're dovetailing one drawer or 50.
A good way to avoid confusion is to label the parts on what will be their inside faces, as shown in the drawing "Organizing the Parts." Being able to read the labels when the parts are in the jig means you've got them oriented correctly. If you are doing drawers, the sides always go on the front, and the fronts and backs always go on the top.
And you need to label more than part names. Consider that each drawer or box has four joints. When you are doing machine-cut dovetails, two of the four joints must be cut on the left side of the jig and two on the right side. You don't want to get them mixed up.
A simple labeling system is shown in the drawing. Where you put the labels is as important as what they are. The letters are always associated with a particular part. Put the letter at the bottom so you know which edge goes against the alignment pins. On the jig itself, mark the two-letter combinations beside each pair of alignment pins, as indicated in the Drawing. As you clamp the parts into the jig, orient the letters toward the pins, and check the combination. If it isn't on your list of two, you are at the wrong end of the jig.
|
 |
Dovetail jigs are "handed." The top edges of your parts must always be oriented to the outside, with the inner surfaces exposed. Thus, the joints on the left of your assembly must be cut on the left end of the jig (left), while the right side joints must be cut on the jig's right (right). Methodically marking the parts, as well as drawing a setup diagram on the jig, can reduce goof-ups that waste materials and time.
|