PROCESS

STEP 1:

Headstock preparation – Cut the wood for the headstock slightly oversized. Clearly mark the centre point on both faces and plane both faces and all eight edges true and square to final dimensions. If you aren’t sure how to lay out an equal-sided octagon with your compass, search for one of the excellent tutorials on YouTube.

Lay out the shape of the cam on both faces of the headstock, accurately following the CAD drawings. Scribe all cam headstock lines crisply and clearly.

If you’re using a dark-wood species for the headstock, make use of 3M blue painter’s tape and lay it carefully and firmly on to the two faces of the workpiece. Once you’ve scribed the cut lines, you simply remove the tape that’s on the waste areas, leaving well-defined layout lines on both sides of the headstock.

STEP 2:

Headstock drilling – Using a 19 mm Forstner bit, drill your beam hole. We recommend doing this on a drill press to ensure the hole is exactly 90° to the faces of the headstock. (Tip: Drill slowly and cut to just over half the thickness of the workpiece. Turn it over and complete the process by drilling from the other side, thus eliminating any tear-out on the faces of the headstock.)

STEP 3:

Making the beam – Setting your headstock aside, it’s now time to create the beam. If you have a lathe, the beam is quick and easy to produce. The final length of the beam is entirely up to you; we chose a length of 270 mm. If you don’t have access to a lathe, making the beam is a little more difficult, but a lot more fun.

Lathe: Turn and sand your beam to an exact diameter of 20 mm. This measurement is critical for the beam to work correctly within the headstock aperture.

By hand: Plane the beam exactly square to 21 mm (oversize) and longer than your required length. Mark the centre of the beam on either end and draw clear circles with a compass at a radius of 10 mm. Then plane the beam with a jack plane to form an octagon, by reducing it at the four facemating edges. Now you’ll have a stick that’s beginning to resemble a large dowel. Next, plane the beam with a small hand plane, using shallow passes until you have removed all of the high points, taking care to work to the circles that you drew on the ends. Follow this up with sandpaper using the 20 mm hole template as a guide. (Tip: A simple method to ensure accuracy of the beam’s diameter throughout its length, whether making it by hand or on a lathe, is to drill an accurate 20 mm hole in a scrap piece of wood that is at least 12 mm thick. Use this as a template to guide your reduction of the beam, until it just slides neatly and comfortably through the template throughout its length without being too loose and without binding at all.)

STEP 4:

Cutting and faring the eccentric cam in the beam – Clamp the beam between two pieces of foursquared stock, a bit longer than your beam. Using a sharp marking gauge and one of the clamped pieces as your reference surface, scribe a line down the centre of your beam according to your scribed layout marks on both ends. This will form the leading edge of the cam. Using a sharp chisel, reduce the beam throughout its length by 0.5 mm ahead of the cam’s leading edge, creating a shoulder. With a shoulder plane, further reduce the surface in front of the cam’s leading edge to a depth of 1 mm. Now, ‘fare’ this area of the beam according to your scribed layout lines with a shoulder plane, card scraper and a little sandpaper as required, gradually faring it in to the 19 mm diameter scribed circle. When viewed from an end, the beam should roughly resemble a large ‘comma’. (Note: When creating the final cam shapes, you’re partially reducing the diameter of part of the beam, and partially enlarging the diameter of part of the hole in the headstock.)

STEP 5:

Cutting and faring the eccentric cam aperture in the headstock – Using a small square file, carefully file away the area behind the shoulder line of the cam to a depth of 1 mm. Using a small half-round file, enlarge the hole according to your layout scribe lines, faring the hole perfectly smoothly.

STEP 6:

Test, fit, test, fit… – Keep faring the headstock aperture until it fits the beam. Note, you should testfit only in the position when the cam shoulders of the two parts are mating. When the beam slides comfortably in the headstock in this position throughout its length, you are done. Now, with a very slight twist of the beam in the headstock, you’ll be able to lock the gauge in any desired position. Unlocking, on the other hand, is simply the reverse action. It only takes a little force to lock the gauge.

STEP 7:

Making and fitting the scribing pin – This component of your gauge should ideally be a hard piece of metal that is sharpened to a fine point. We used a standard drywall screw and hand filed it to suit. We then drilled a hole and countersunk the screw into the beam

12 mm from the end.

STEP 8:

Finishing – Once you’re entirely happy with the action and finish of your new tool, apply your favourite finish to the project. We used Osmo Polyx-Oil 3011 Clear Gloss Hard Wax Oil. We applied three extremely thin (almost non-existent) applications with a non-abrasive pad, and after ten minutes we burnished each application hard by hand with dry, lint-free paper pads. Each application of the Osmo Polyx-Oil was left to cure for a full eight hours, before applying the following coat.

Above: Sawing the Macassar ebony headstock. Below: Drilling out the Macassar ebony headstock on the drill press for accuracy.

Finishing the marking gauge parts with Osmo Polyx hard wax oil.

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MAY / JUNE 2021 Above left: The MDF template used for exact hole sizes. Left: Crisp layout of the eccentric beam profile. Right: Scribing the cam edge using two boards as the parallel reference.

Using a shoulder plane to create the cam profile throughout the length of the beam.