How do you get the perfect fit? What works for me is to first cut the joint to fit on the snug side. The idea is that you want to be able to get the tails started over the pins with some firm pressure, but not much farther without extra force. At this point,
Rub the Tails. To find the tight spots between the pins and tails, first use the side of a pencil to mark along the inside edge of the tails.
or gentle taps from a mallet will seat the joint tightly.
TOO TIGHT. If your completed joint is so tight that only forceful hammering will drive it together, you can expect problems. The tail piece can actually be split by the wedging action of tight pins. Or the outside edge of a tail can "blow out" as the joint is forced together.
The High Spots. When you press the tails over the pins, the graphite will rub off on the high spots and show you right where to trim.
When you use through dovetails on a project, cutting them is only the first step. The real challenge comes in doing that little bit of extra work that gives you a seamless fit between the pins and the tails.
Whether you cut your dovetails by hand or with a jig, as I did for the tool chest on page 32, the final "tweaking" that gives you a perfect fit doesn't have to be tricky or tedious. It just takes a little patience and a few simple tips and tricks.
A GOOD DRY FIT. The first thing you need to think about is what kind of dry fit will lead to an easy assembly and a perfect-looking joint. What I try to shoot for is a fit that takes only light pressure to assemble. The tails should fit oveT the pins easily, requiring only firm hand pressure to force the joint most of the way home. A few light blows from a fist
some careful trimining with a sharp chisel will get you to a perfect fit.
WHERE TO TRIM. You don't want to start trimming without knowing where the "tight spots" are that need work. The simple marking trick shown in the drawings on the opposite page solves this problem.
You'll notice that I'm marking and then trimming the tight spots on fine pins. Since the sides of tine pins are usually better exposed, it's easier to see the graphite that's rubbed off on the high spots. And it's easier to get at the pins to trim them to fit.
TRIM TO FIT. Once you know where to trim, you can get started. For this "fine tuning," my tool of choice is generally a Vi'-wide chisel (photo at left). A narrow chisel allows you to make controlled cuts over a small area and get into tight corners. And it's easier to see what you're doing.
When I start to trim away the high spots, I pare from the side (cross-grain) rather than the end. Working crossgrain, you won't have to worry about the grain direction of the pin face. With a sharp chisel and a light touch, you can slice the wood fibers cleanly and easily.
UP THE SLOPE. I do as much of the work as possible working up the slope of the pin (photo at left). This seems to give me a little better control. But you want to avoid cutting
Reverse Directions. After doing most of the trimming up the slope, reverse directions to complete the job.
clear across the sharp corner of the pin. It's likely to chip off instead of cut cleanly. So I'll stop short of the edge and then come at it from the other direction (left drawing above).
WATCH THE EDGES. When trimming the pins, I always try to be very careful near the edges. The bevels on the pins and tails can chip way too easily. If possible, I stay clear of the edges and limit my cuts to the inner face (left drawing). But if you have to trim clear to an edge to get a good fit, always work from the "outside in." This way, the wood is backed up and won't chip out.
TRIM AND TEST. A perfect fit doesn't come all at once. Pare a little bit and then test the fit. If the joint is still too tight, go through the marking
A Slight Undercut Undercutting the faces between the pins ensures the joint will close up tightly.
process again and trim a bit more. But patience at this point pays big dividends when it comes to the final assembly. It often takes me several rounds of trimming and testing before I get it right.
UNDERCUT. For me, the final step just adds a little insurance. I take my chisel and undercut the space between the pins slightly, as shown in the right drawing above. This ensures that the pins and tails will pull up tightly when clamped. You can avoid gaps by leaving a narrow "flat" along the outside edges
Now, one corner is a perfect fit and you're ready to move on to the next. When all four comers are ready to go, the glue-up tips in the box below will help you finish the job. E£9
How To; A Perfect Assembly
Just a Little Glue. A bead of glue on the ends of the pins and the mating edges of tails will spread across the joint when the pieces are assembled.
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