Make a Depth Gauge
For most of us, measuring depth is just a matter of putting a ruler into the mortise and taking a reading. However, there are times when even our skinniest ruler won’t fit. That’s where a depth gauge comes in.
Knowing the depth of mortises or stopped holes is important for joinery. While there are lots of versions out there, from expensive ones for machinists to cheap bargain-rack types, we are woodworkers and we can make one that not only works well, but looks great.
With all the necessary hardware on hand, Der-Garabedian lays out the shape of his gauge on graph paper, applies the paper to the solid workpiece, then cuts out the body of the gauge.
To secure the brass plate to the base of the gauge, use epoxy – light clamping pressure is best when using epoxy. During this stage ensure the brass extends beyond the solid wood gauge on all sides.
After drilling the hole for the insert nut, drive the insert nut into the hole. Some wax will assist you, especially if the wood you’re using is fairly dense.
Hole for Depth Rod
While drilling the hole for the depth rod, insert a brass bolt into the insert nut. The bolt will stop the inner threads on the insert nut from being bent out of shape and becoming unusable.
Though the epoxy will likely keep the brass secured to the gauge body without any problems, Der-Garabedian liked the look, and the added insurance, of a few carefully counter-sunk screws.
On an edge or drum sander, shape the body of the gauge to its final shape. The edges of the body and brass should be flush after this step.
Some hardware required
As with most projects that require hardware, it’s a good idea to have it on hand before starting. Your local metal supplier, or craft shop, will have some 1/8″ thick flat brass 1″ wide. You’ll also need to pick up a 1/8″ diameter brass rod. The shortest these come are usually 12″ and should cost about $5 and $2, respectively. Lee Valley Tools will have the rest including 1/4-20 insert nuts (00M90.01), a 1/4-20 knurled screw (00M91.01) and a 1/4-20 brass bolt (44Z09.03) but these items are also available at other specialty hardware stores across the country.
The process of creating a depth gauge is not difficult, but requires a specific order of operations. Mill a piece of hardwood to 3/4″ x 1-1/2″ x 12″. The extra length is just so the blank can be power-planed to thickness. Black walnut adds a nice bit of contrast to brass, but most solids – especially exotics – look great beside brass. Draw a pleasing shape on some graph paper, cut it out and attach it to your blank with either double- sided tape or spray adhesive. A good width for the gauge is 4″. Continue your center line onto the blank and draw crosshairs marking the location of the depth rod’s through-hole and the location of the insert nut. The depth rod’s hole is centered across the thickness of the blank, in this case 3/8″. Center the insert nut, making sure to leave enough material around it so as to not split the wood when screwing it home.
Time for brass
Cut your brass plate adding 1/16″ on all sides with a hacksaw. The extra width and length allows you to flush all the surfaces down the road. Sand one face of the plate with 120x sandpaper, leaving a rough surface for the adhesive to bond to. Mix a small batch of 5-minute epoxy and lightly clamp the brass plate to the blank, making sure there is over-hang around your drawn shape. Once the epoxy has cured, lightly sand the brass bottom of the gauge using 280x sandpaper. Take care to keep it flat and not create a wedge.
Next, use a 3/8″ bit and drill 1/2″ deep into the face of the gauge for the insert nut at your marked point. Use a block underneath your blank to keep the body perpendicular to the drill bit. You’ll also want to secure the gauge during the boring process. Apply a bit of wax to the threads of the nut and screw it in, making sure to keep it straight. As our depth rod is 1/8″ and we want it to slide smoothly, drill a 9/64″ hole from top to bottom. Threading a 1/4-20 brass bolt into the insert nut before this operation will keep the female threads from being damaged.
While there are no stresses being placed between the hardwood body and brass plate, the epoxy should be more than strong enough to secure the two. However, adding a couple of #4 x 1/2″ flat-head brass screws adds a nice touch. Remember to counter-sink for the heads of the screws.
Sand the back of the gauge with a belt sander until the brass plate is flush with the hardwood body. Take your assembly to the bandsaw and rough-cut the shape close to your outline. Head back to your power sander and sand the body until you achieve your sketched shape. Remove the graph paper and flush the front of the brass plate with the body.
Ease the edges of the gauge, including the brass bottom, and rub on a bit of wax for protection. Another option would be to add a few coats of your favourite finish. Slide your depth rod in, lightly pinch it with the knurled screw and your depth gauge is ready for use.