How to Cut Through-Dovetails That Actually Fit: The Marking-Gauge Workflow

Sunday in the shop, coffee's on….. and I've got dovetails on my mind. A dovetailed tool chest, a seat box, a locker box for the boat: it's the same corner joint every time, and every time it either fits right off the saw or it doesn't. Here's the thing nobody tells you when you start. Most gappy dovetails are lost at layout, not at the saw. So today it's the through-dovetail start to finish, built around the one tool that decides the fit before you ever cut: the marking gauge.

Why it matters: The slope of the tails is what locks the corner and draws the pin board up tight (Chris Gochnour, Fine Woodworking), and the long-grain glue surfaces do the rest (Lonnie Bird, Popular Woodworking). Bird puts it plain: dovetailing is just sawing and chiseling to a line, and if the line is wrong the joint won't fit. The gauge line is the line your chisel drops into on both boards. Set it once off the wood itself, use it everywhere, and half the battle's won. Get it wrong and you're filling gaps with glue and sawdust, and everybody can see it from across the room.

Materials

• Two boards dressed flat, the same thickness all the way across, with the ends cut square (Lee Valley). For a chest, the tails go on the front and back and the pins go on the ends (Gochnour).
• Practice scraps first. Lee Valley says skip the really soft stuff while you're learning, because the fibers crush; poplar, walnut or cherry are friendlier.
• A sharp 0.5 mm pencil, to darken lines and mark the waste
• PVA glue for a shop chest (Lee Valley's call in their instructions)

Tools

• A marking gauge, wheel or pin, and sharp. A dull one tears the end grain instead of cutting it (Bird). If your two boards aren't the same thickness, use two gauges, one for each.
• A marking knife (a striking knife is best, says Lee Valley)
• A sliding bevel or a dovetail marker in 1:6 and 1:8
• A combination square, and a pair of dividers for spacing the tails (Gochnour)
• A dovetail saw. Dovetailing is a ripping cut, so it should be rip-filed; Lie-Nielsen's is 15 points per inch with a .026 in. kerf. A Japanese dozuki pull saw works fine too (Bird).
• Bevel-edge chisels, including a narrow one, 3/8 or 1/2 in., for chopping, plus a mallet. Bird likes a short chisel and a round 12-ounce mallet.
• A block plane, to bring the proud ends flush after glue-up

Steps

1. Mark the boards before anything else. Inside and outside faces, top and bottom, which board gets tails and which gets pins (Gochnour, Lee Valley). A cabinetmaker's triangle on each pair takes ten seconds and saves the one mistake you can't fix: assembling a perfect joint upside down.
2. Set the gauge off the wood, not a ruler. Pinch the mating board between the fence and the cutter (Lee Valley). That's your baseline depth. Gochnour sets it to the exact thickness of the pin board so nothing stands proud to get in the way of the clamps. Bob Van Dyke (Fine Woodworking) says the most common practice is a hair more, so the pins and tails stand a little proud and get planed flush. How much is a hair? Woodsmith suggests 1/64 in. for beginners, Canadian Woodworking about 1/32 in. Go 1/32 to 1/16 in. over and you're into deliberately proud pins, a look of its own (Van Dyke). Then lock the gauge and leave it alone until both boards are marked. If the boards differ in thickness, the tail board gets gauged to the pin board's thickness and the pin board to the tail board's.
3. Gauge the baselines on both boards. On the tail board, run the line around all four surfaces: both faces and both edges. On the pin board, both faces (Lee Valley, Bird). Keep the gauge head hard against the end, and make several light passes instead of one heavy one so you don't tear the grain (Bird). A pencil over the line helps tired eyes.
4. Lay out the tails. Leave at least 1/4 in. at each edge for the half-pins so the boards don't split at assembly (Lee Valley). Gochnour sizes half-pins 1/4 to 3/8 in. and inside pins 1/8 to 1/4 in. at their narrow end, spaced 1-1/4 to 2 in. on center for a big case like a chest. Walk the spacing off with dividers. For the slope, the traditional ratios are 1:6 for softwood and 1:8 for hardwood (Gochnour, Lee Valley). That's about 9.5° and 7.1°; the exact numbers are arctan(1/6) = 9.46° and arctan(1/8) = 7.13°. To set a bevel without a protractor, square a line in from the edge of a board and mark 8 in. up it, then mark 1 in. along the edge from where the line starts, and join the two marks. Stock on the edge, blade on that line, and you've got 1:8 (Gochnour sets his off the 1-in. and 6-in. marks for 1:6). A white pine chest gets 1:6; a mahogany or oak seat box gets 1:8. Don't lose sleep over it: Fine Woodworking says anything from 7° to 15° works in any wood, and Christopher Schwarz cuts his at 14°. Square the lines across the end grain and put an X in every piece of waste (Lee Valley).
5. Saw on the waste side and leave the line. The line belongs to the tail. Saw slow, with long strokes and very little downward pressure, and let the saw track (Lie-Nielsen). Bird angles the saw, not the board: clamp the board level, make every cut that leans one way, then every cut that leans the other. Keep the saw level as you come down to the baseline and stop right on it (Lee Valley). Then lay the board flat and saw the half-pin waste off the ends, square, without nicking the tails.
6. Chop to the line. A saw kerf or two down the middle of the waste gives the chips somewhere to go (Bird, and a Fine Woodworking reader tip). With the board flat, start the narrow chisel about 1/16 in. back from the baseline and drive it about halfway through. Then set the edge right in the gauge line, which it'll drop into, lean it a hair for a slight undercut, and chop again (Bird, Lee Valley). Flip the board and do the same from the other face. Undercut the middle, never the faces: a nicked corner shows forever. When you're done you should see a whisker of the gauge line left at the edge (Bird). No line, you went too far, or not far enough.
7. Transfer the tails to the pins with a knife. Pin board in the vise, outside face toward you, its end flush with a prop beside it, a scrap or a plane on its side (Lee Valley). Lay the tail board on top, edges flush, and put its baseline exactly on the inside face of the pin board (Gochnour). If the baseline sits on the end grain, the joint will be too tight. If it hangs past the inside face, the pins come out small and the joint's loose. Hold it hard, or clamp it, and knife around each tail with several light cuts (Lee Valley). Square those marks down the face to the baseline (Gochnour) and X the waste right away. Saw on the wrong side of a pin line and you've bought yourself a loose joint (Lee Valley).
8. Saw and chop the pins. Same rule: saw on the waste side so the knife line stays on the pin. On the pin board the saw stays plumb, straight down the length of the board; the angle is across the end grain. Down to the baseline, level, then chop the waste exactly as you did the tails, without letting the chisel bite into the angled pins (Lee Valley).
9. Test fit with pencil lead, then glue and flush it. Scribble pencil on the sides of the tails, push the joint together by hand until it starts to resist, then pull it apart. Wherever the lead rubbed off onto the pins, that's what's binding; take it down with a chisel or a file and try again (Gochnour, Fine Woodworking). A good one goes together with very little effort (Lee Valley): thumbs, or a few light taps of a dead-blow on a wide case (Bird). Glue it up, and once it's dry, plane the proud ends flush. Work from the outside edge in toward the board so you don't blow out the unsupported fibers at the back (Katz-Moses Tools).

MOAM's shop note: The most common mistake I see isn't bad sawing. It's a gauge that got bumped between the first board and the second, or a waste piece that never got its X and got sawn on the wrong side of the line. Set the gauge once, mark every baseline on every board, and only then put it down. Pro trick from Bob Van Dyke, who learned it from Steve Latta: cut a very shallow rabbet across the inside face of the tail board, right on the gauge line. That little shoulder hooks over the pin board and puts the baseline exactly where it belongs while you knife the transfer. A strip of 1/4-in. MDF clamped on the baseline does the same job. And for the record, Paul Sellers skips gauge lines altogether. He calls them bruised wood and uses a knifewall instead. Fair enough on fine furniture. On a tool chest or a boat box, that little line is honest work, and I'll leave it.

Sources: Chris Gochnour, "Laying Out Dovetails," Fine Woodworking #190, and "File Joints for a Perfect Fit," Fine Woodworking #247; Bob Van Dyke, "More Than One Way to Cut a Dovetail," Fine Woodworking #311; "Designing Dovetails for Strength and Style," Fine Woodworking; "Relief Cut Makes it Easy to Chop Out Dovetail Waste," Fine Woodworking #276; Lonnie Bird, "How to Cut Dovetails by Hand," Popular Woodworking; Glen D. Huey, "Dovetail Layout: What Ratio or Degree?" and Christopher Schwarz, "Dovetail Angles are Style, Not Substance," Popular Woodworking; Lee Valley/Veritas, Dovetail Saw Guide instructions and Dovetail Markers; Lie-Nielsen Toolworks, Dovetail Saw; Paul Sellers, "Gauge lines on dovetails"; Woodsmith, "Hand Cut Dovetails"; Canadian Woodworking, "Hand Cut Dovetails"; Katz-Moses Tools, "Cutting Your First Dovetails."

MOAM Out.

Tools for this tip

As an Amazon Associate I earn from qualifying purchases.

• Taytools wheel marking gauge, solid brass head: one setting, pinched off the mating board, for every baseline on both boards
• Narex double-bevel marking knife: knifing the tails onto the pin board with light, repeated cuts
• Gyokucho 770-3500 razor dozuki saw (fine-tooth pull saw for dovetails): a thin-kerf pull saw that tracks on the waste side of the line
• Narex Premium bevel-edge chisel set (4 pc): chopping the waste to the gauge line and paring the fit
• Starrett 12-inch combination square (11H-12-4R): squaring lines across the end grain and down to the baseline

Use whatever you already have in the shop; these are just the ones that fit this job.