Once you've collected the tools to do the job, it's time to start laying out the cuts. There are three basic variations on the dovetail joint: through dovetail, half-blind, and mitered (or full-blind).
Although much of the process is very similar for all three variations, we're limiting this article to through dovetails. Half blind dovetails (which are used mainly in drawer construction) will be covered in the next issue. And mitered dovetails won't be covered at all because they have extremely limited application (and they're really kind of a waste of time).
through dovetails. The method described here for cutting through dovetails may not be the best. It's certainly not the fastest. But it is satisfying work . . . done with hand tools.
A through dovetail joint consists of two halves: the pins and the tails. The worst part about laying out a dovetail is getting a clear picture in your mind of what these two halves look like and how they fit together. This just takes a little getting used to.
When viewed from the face sides of the boards, the pins of the dovetail (the board on the right in the photo) look just like the rectangular pins of a box joint. The tails (the board on the left in the photo) look like a dove's tail (hence the name of the joint).
Just to keep you on your toes, when viewed from the ends of the boards the pins look like tails, and the tails look like pins. But this confusion will clear up after you've cut one or two dovetail joints.
Now the question arises: Which board gets the pins, and which board gets the tails? And does it make any difference? Although a dovetail is commonly considered a very strong joint, it is only strong in one direction. (Here I mean the mechanical or interlocking strength of the joint. Once it's glued up it's nearly impossible to get apart in any direction.)
The direction of strength is toward the pins. To illustrate, refer to the drawing at right. Dovetails are normally used to join four boards at right angles to form a box. If this joint were on a drawer, for example, the pins would be cut on the drawer front where the mechanical strength of the joint holds the drawer together as it's pulled open. If the joint were on a wall-hung cabinet the pins would be cut on the bottom which is the direction of the weight of the contents.
However, the direction of mechanical
strength of the joint may not be the primary consideration. If the box is meant to support weight from the outside (as with the Shaker Step Stool in this issue), the direction of pressure (or weight) is more important. This has to do with the size and placement of the tails. The tails, in this case must be wide enough to support the weight (downward pressure) on the face of the board, and positioned so they take the brunt of the weight.
direction of weight f
In some cases both direction of strength and direction of pressure must be considered — as with the coffee table in this issue. The pins are on the legs to keep them from splaying out, which wrorks out nicely because the tails must be on the top to support the wreight.
What's the first step in laying out a dovetail? At this point I'm supposed to launch into a discussion about pins and tails, and angles, and such. But the first step (indeed. the first three steps) have nothing to do with pins, tails, or angles.
1. truing the boards. The first (and often neglected) step is to true up the boards you'll be working with. I rip the boards to width, making sure both edges are ripped square. (The edges can be smoothed on a jointer or with a hand plane, but I usually wait until after the dovetails are cut for the final smoothing.)
Next, both faces of the boards should be planed or sanded to remove any defects (such as 'ripples' left by a surface planer), or to remove any 'cup' or twist in the boards. Also, make sure the thickness (particularly at the ends of the boards) is equal from one edge to the other.
In other words, the boards should be flat and smooth — to the point that all they need is a little finish sanding. This will ensure things don't get goofed up during the layout phase.
2. CUT TO LENGTH. Now the boards can be cut to length. However, the final length of each board depends in part on step three (which deals with marking the base line, or shoulders of the joint). But for now, let's assume the boards are cut to length for a box. The key thing here is to make sure the ends of the boards are cut square with the edges.
If neither the inside or outside dimensions of the box is absolutely critical, then the boards can be cut to length without much concern if the actual final dimensions vary a little.
However, in drawer work, especially when the drawer must fit in a specific opening, the procedure followed in Step 3 must be taken into consideration first.
If all of this is too much, the real point of Step 2 is to make sure the ends of all boards are square with the edges.
3. mark the shoulders. The boards are true, the ends are cut off square. Nowt all that remains is marking the base line (the shoulders) of the pins and tails. This base line is actually the bottom of the cut on both pieces, and in effect dictates the final dimensions of the box.
The base line also dictates the amount of work you must do during the final cleaning up stage. Without getting bogged down in too much detail, you have three choices. The base lines can be marked exactly at direction of weight f
the thickness of the boards, or a tiny smidgen more than the thickness, or a tiny smidgen less.
How the base lines are marked is important for two reasons. The base lines determine the final measurements (the final length) of the boards you're joining together. If you're building a drawer, for example, this measurement becomes critical because the distance between the base lines actually determine the final width of the drawer.
The second reason has to do with the amount of work you have to go through to clean up the finished joint. Let's say, for example, that you're going to build a drawer. All four corners are joined with through dovetails. The pins are cut on the drawer's front and back, and the tails are cut on the sides.
The basic procedure for marking the base lines is to use the thickness of the board for the tails (in this case, the sides) to set the marking gauge. Thus, when the base line is marked on the drawer's front, the distance between the base line and the end of the board is equal to the thickness of the drawer's sides.
Most books say to set the marking gauge a little more (just a hair more) than the thickness of the second board (the drawer's side). The result is that the pins will stick out just a hair beyond the face of the sides when the joint is complete. They must then be cut, filed or planed down flush.
I like to mark the shoulders just a tiny smidgen less than the thickness of the second board. This means the ends of the pins are recessed slightly, lb clean up the finished joint, it's now quite easy to use a plane to clean up the joint. After planing the sides a little bit, the plane gets down to the end grain on the pins, making it nice and smooth. Also you'll be removing the shoulder (scratch) line at the same time.
By this time you're probably getting tired of reading all this preliminary stuff about dovetails. But I would like to make a few-more general comments concerning layout.
Laying out the joint — the size and placement of the pins and tails — is well worth some time and thought. If you rush into the actual cutting, you may end up with a joint that's cut precisely, but looks clumsy, or worse . . . boring.
The best procedure is to draw the pins and tails on a piece of paper ( or on some scrap wood). You should mark out all the details of the size and placement — and feel comfortable with them — before taking saw in hand.
marking the pieces. After cutting the pieces to size and truing them up, it is very helpful to mark the inside and outside faces of each board to avoid confusion. 1 simply w rite in large letters "IN"' and "OUT' near the end of each board where the dovetail is to be cut.
Most of the time you'll be cutting dovetails on several boards to form a box or drawer. Since this is all handwork, the size of the pins and tails will undoubtedly vary from board to board. It's best to clearly mark the two boards (the corners) that will go together.
w idth of pin vs. tail. One way to lay out the cuts for a dovetail is to use a ruler to divide the board for the pins into equal spaces. Then the pins and the spaces between the pins (which will be the tails) are laid out at equal widths. This is easy but very boring. Since the pins and tails are nearly the same size, the dovetails look as if they are machine-made, as shown at the top in the drawing.
It's a matter of individual preference, but I prefer the pins to be quite narrow-compared to the tails. As a general rule I use a minimum 1:4 ratio for the relationship between the pins (1) and tails (4). For
1:4 ratio for pins to tails
! & i
pins equal width, tails increase at center
example, if the narrow est part of the pins (the outside face) is V«" wide, then the tails should be at least 1" wide.
When it seems appropriate, I think it's nice to keep all the pins the same size, but vary the width of the tails. The tails nearest the edges of the board are the smallest, while those on the middle of the board are wider. (The layout of the joints on the Coffee T&ble are done this way.)
As you lay out the position of the pins, there should be a half pin on the two outer edges. (Half pins are not necessarily one-half the width of any other pin, it's just that they're cut on only one side). The position and spacing of all the other pins (those betw een the two half pins) is a matter of choice.
After laying this all out on paper, I transfer the marks for the position of the pins with a 12" steel ruler. These marks will indicate the narrowest width of the pins. However, you can save a lot of hassle later if the narrowest part of the pins is marked off with the chisel you're going to use to chop out the waste.
As showrn in the drawing (above, right), the marks are placed just a smidgen outside the width of the chisel to allow some room. (This method is discussed more in the section on cutting the tails.)
angles. The last consideration is the angle used for layout. The general rule is that a 1:5 angle is used on soft woods, and a 1:7 or 1:8 is used on hardwoods. The difference has something to do with the strength of the wood.
I prefer a 1:5 angle on any wood just because I think it looks nice. Once again this a matter of personal (visual) preference. A 1:5 angle translates to 78V^°, while a 1:8 angle is about 83°. That may seem like nit-picking, but there is a definite visual difference. Anything less than 1:5 makes the 'neck' of the tails look disturbingly weak, while more than 1:8 looks like a box joint.
To set the sliding bevel at the proper angle, I use a small piece of plywood. First, draw a line exactly 90° to a good clean edge. Along this line mark a point 5" (or 8", or whatever you want) from the edge. Then draw another line perpendicular to the first one, and mark a point 1" to the left or right. Position the body of the sliding bevel along the edge of the plywood and then adjust the arm to the mark that gives you the angle you want.
pins or tails. Which do you cut first, the pins or the tails? In the case of through dovetails, it's generally accepted that it doesn't make much difference which is cut first. However, I mark and cut the pins first for three reasons.
First, I think the pins are easier to cut and I like to get started with the easy part. Second, whichever half is marked first (the pins in my case) is used to mark the lines for the second cuts (the tails). I think it's much less awkward to position and hold the boards if the pins are cut first and used to mark the lines for the tails. The third reason is that I find it easier to check the accuracy of the finished cuts on the pins (and do any correcting) than it is with the tails.
Now you're ready to cut the pins.
mark lines to outside of chisel chisel
chisel mark lines to outside of chisel
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