Adjustable Dovetail Gauge

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This article is from Issue 65 of Woodcraft Magazine.

Two quick-set angles and everything in between

Overall dimensions: 9⁄16"w × 51⁄4"d × 61⁄4"h

I use a lot of hand-cut dovetails for my furniture, and for two good reasons: they’re strong and, when the joinery is exposed, they’re beautiful. To make laying out easier, I designed this shop-made dovetail gauge that ensures accuracy and speeds up the process of marking tails or pins. As a bonus, it’s a beautiful addition to any hand-tool collection.

This gauge is made with a mahogany head and a rosewood blade. An angled mortise in the head registers the blade at one of two favorite dovetail angles (in my case 5° and 14°), or it can be set to any angle in between. A friction-fit allows pivoting the blade without tools. The head provides bearing on both sides of the blade, so the tool can be flipped to mark out complementary angles.

The long blade allows marking out dovetails for everything from typical drawers and cases to wooden vises for a workbench, and other thick pieces that demand long tails and pins.

Construction of the gauge is simple, as there’s no fussy mortising involved in making the head. Instead, you simply laminate four strips of wood together, mitering the two in the middle and leaving space between them to create the mortise. For the critical friction-fit of the blade, all you need are a few swipes with a sharp plane.

When mitering the end of the gauge blade, use a hold-down board, resting its far end on a shim of equal thickness to the workpiece. MDF underneath prevents tear-out.

Make the head and blade

1 Select straight-grained stock for the head. I used mahogany, but any favorite hardwood will suffice. Starting with an oversized blank roughly 1 × 11⁄4 × 12" long, resaw it into three pieces about 1⁄4" thick, and mark them for reassembly in the same orientation later.

2 Pick an even denser wood for the blade, such as rosewood, wenge, or even a dense domestic wood such as hard maple or beech, again selecting straight grained stock. Mill the blade to about 1⁄4 × 7⁄8 × 12" long for now.

3 Thickness-plane the head pieces and the blade, taking very fine passes and planing the head pieces to 3⁄16" thick. Stop planing the blade on the last few passes, leaving it thicker than the head pieces by 1⁄32" or so for now. You’ll hand plane it to final thickness later.

4 Joint, rip, and crosscut the blade to the final width and length shown in Figure 1.

5 Sand the ends and narrow edges of the blade through 320 grit, keeping the edges square. Don’t touch the faces for now.

6 Separate the middle head stock piece in two, using a mitersaw to cut the two different miters at the center of the piece (Photo A).

Note: Dovetail angles ranging from 7° to 14° are traditional, but I used a 5°/14° combination because I prefer 5° for thicker casework, and 14° for small drawers and boxes.

Glue and clamp the middle piece with the more acute miter first, and then butt the blade against it and attach the opposing middle piece with its tip touching the blade.
After the glue cures, cap the assembly with the remaining head piece, using both full-length clamping blocks and checking for edge alignment.

Gluing up the head

7 Make four clamping blocks from 1⁄2" MDF or plywood sized to the width of the head pieces. Make two of the blocks an inch or so shorter than the outer head pieces, and two blocks an inch shorter than the middle pieces. (The shorter lengths allow better visibility during glue-up.)

8 Spread a thin film of glue on one face of the inner head piece that has the more acute miter. Place it on an outer head piece with the mitered end near the center, and the long edges aligned. Then clamp the pieces together between a long and a short clamping block.

9 Place the blade against the miter on the attached piece, and then glue the opposite inner head piece in place with the tip of its miter touching the blade. Clamp it as shown in Photo B, remove the blade, and set the assembly aside for at least an hour.

10 Remove the clamps and spread glue on the middle head pieces. Add the second outer piece, and clamp the parts together as before, but use both long clamping blocks this time (Photo C).

11 Once the glue has dried, pare away any squeeze-out from inside the mortise using a narrow chisel, and then plane or joint the long edges flush. Be careful not to remove too much material or you’ll widen the mouth of the mortise.

12 Lay out the curved ends on the head, as shown in Figure 1, keeping the mortise centered. Bandsaw the ends just shy of your layout lines, and then sand to them.

13 Finally, round over any sharp edges and smooth all the surfaces by sanding through 320 grit. I sanded small 1⁄16" chamfers on the ends of the head using 320-grit sandpaper wrapped around a hard block.

Planing against a stop strip thinner than 3⁄16", take fine, full-length shavings from each face of the blade in turn until you achieve a friction fit in the mortise.

Fit the blade and finish up

1 Use a sharp block plane to finesse the thickness of the blade for a solid friction-fit in the head. As shown in Figure 2, first adjust the plane for a very light cut, and take a full-length shaving from each face of the blade (Photo D). Check the fit, and keep taking full-length shavings until both ends almost enter the longer end of the mortise, or do so with a fair amount of force.

2 Starting about 2" in from each end and on both sides of the blade, take a single very fine shaving outward. Check the fit and, if necessary, repeat the process until each end of the blade slides easily into the mortise and the blade snugs up tight at its center.

3 Sand the planed faces of the blade with 320 grit, touching the center only lightly to avoid altering its fit. Sand the edges, but not too much, as they need to remain crisp for accurate marking. Finally, sand a 1⁄16" bevel on the ends of the blade.

4 Finish the blade and head, applying a couple coats of a penetrating finish such as oil or thinned wiping varnish, letting it soak in before wiping off the excess. Smooth between dried coats with 0000 steel wool, apply wax, and buff it out.

5 To set the gauge to one of the two fixed angles, grasp the ends of the blade with both hands, wrapping your thumbs around the appropriate end of the head, and squeeze the blade against the end of the mortise. 

About Our Author

Andy Rae is an award-winning furnituremaker whose career spans several decades. He has authored a number of books on woodworking, including Choosing & Using Hand Tools (Sterling Publishing) and Furniture and Cabinet Construction (Taunton Press). He lives in the mountains of western North Carolina.


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