Mystery of the Marking Gauge

Many commercial gauges are missing excellent features found on traditional versions.
By Dean Jansa
Pages: 36-39

From the December 2006 issue #159
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Note: For the complete article including the special segments on “Types of Gauges” and “Marking Gauge Pins – Where’s the Flat?” download the complete PDF of the article.

The simple marking gauge, often overlooked, even taken for granted, is critical in the hand-tool shop. It allows you to create uniform surfaces quickly with planes, to accurately transfer measurements from one board to another and to help duplicate measurements across similar parts.

Inventories of 18th-century toolmakers show that they made gauges for sale, but the inventories also show quantities of marking gauge pins that woodworkers would use to build their own gauges. Despite the fact that these pins are no longer commonly found for sale, you can build a gauge – a gauge superior to mass-produced gauges – with common shop sundries and wood from your offcut pile.

Building a Gauge
I chose to copy a marking gauge found in the tool chest of Benjamin Seaton, an 18th-century English chest that has survived with most of the original tools intact. This simple gauge, sometimes referred to as a “French gauge,” offers features often absent on modern gauges: You can adjust and lock the gauge with one hand thanks to a captive wedge, and the head has a comfortable shape, which helps you direct pressure and control the depth of cut.

The basic dimensions of the gauge as shown are not set in stone. Feel free to modify the dimensions to fit your needs. For example, I made my gauge arms a bit shorter than the original Seaton gauges so they would fit in my tool chest’s trays. I recommend you make the arm’s width and thickness match a chisel width available in your kit. The head of the gauge can be scaled to fit your hand.

Gauges made of beech and birch were common, however hard and soft maple, cherry and mahogany work as well. Use 6/4 stock for the head of the gauge and straight-grained 4/4 stock for the arm. Pins made from 4d finishing nails or cut brads are soft and easy to shape; however, they do not hold an edge as long as a harder material. Twist drill bits (I use 5⁄64″) are easy to shape on a grinder and take and hold an edge well. Use the photos and illustrations on the right to build the gauge.

Using the Gauge
The head shape and captive wedge of the Seaton gauge offer benefits compared to a modern mass-produced gauge. I hold the gauge with my thumb and index finger, wrapping my hand over the top of the head. My free fingers fall naturally around the arm. Holding the gauge like this allows me to lock, unlock and adjust the gauge with one hand. The reason for the bevel on the bottom of the head – indeed, the reason for the overall shape of the gauge – became clear to me the moment I held a completed gauge. It was an “a-ha” moment in my shop.

With your hand in this position you can scoot the head forward or backward with your thumb. If the head slides too freely on the arm, lightly engage the wedge to create friction. Once the desired setting is achieved, press the wedge with your thumb. A final light tap on your workbench firmly locks the gauge. A quick tap on the opposite side of the wedge unlocks the gauge.

In use, the gauge’s pin is rarely perfectly perpendicular to the work, rather it trails behind the arm. The closer to vertical the pin, the deeper the gauge cuts. You control this angle by rolling your wrist about the gauge arm.

When making long-grain marks I make my first pass with the pin barely engaged with the wood. If a deeper mark is required – in coarse-grained wood for example – I make a second pass with a more aggressive angle of attack. Cross-grain marking requires a lighter touch to avoid tear-out. Despite shaping my pins like small knives, I still use a very low angle of attack for cross-grain marking.

You can use this wrist-rolling technique to speed up marking mortises. Mark the start and end points of the mortise with a marking knife. Next set the gauge to the appropriate offset from the face. With the gauge’s pin very lightly touching the wood, drag the gauge until you feel the pin drop into the mortise start point. Roll your wrist to deepen the cut and mark until you feel the pin intersect with the mortise endpoint.

Gauging, Not Measuring
Gauging is the use of a tool to transfer a measurement from one board or surface to another. For example, in casework you set a marking gauge with the mating board when marking dovetail baselines. Using a gauge to lay out dovetail baselines eliminates errors by avoiding transferring measurements from a ruler.

Creating Uniform Surfaces
Uniformly thick boards can be quickly made by hand using this gauge as a guide. Begin by flattening one face of the board. Then use the gauge much like a dial caliper and find the thinnest spot in the board. Set your gauge at that point, mark the thickness around the board’s four edges, and plane down to the mark. Working this way saves any extra effort needed to create a uniform board. You are removing only the minimum amount of material necessary for uniformity. Not all 4/4 lumber need be 3⁄4″ thick.

Repeatable Measurements
Creating a number of boards of the same thickness or width follows a similar set of steps. Set the gauge to a board of the desired thickness or width and mark each remaining board with the gauge. The gauge will be correct. Each mark will be exactly the same as the last. Your results are repeatable.

Combining gauging, uniformity and repeatability speeds your work. If you need a number of uniformly thick boards, begin by flattening one face of each board. Then find the thinnest spot on the entire group of boards.

Mark the remaining boards with this setting and plane each board to the mark.

Large panel glue-ups can also use this technique. Face joint the individual boards. Match plane the edge joints and glue up the panel.

After glue-up, make any necessary adjustments to the face side of the panel. Again, find the thinnest spot remaining in the panel with your gauge, mark the panel thickness, and plane to the mark. This eliminates planing the non-face side of the boards twice.

Conclusion
The simple marking gauge is a critical tool in the hand-tool shop. From stock preparation to cutting dovetails, the gauge plays its role. It improves your speed and minimizes your effort with planes. It offers lessons about building accurately by defining what you need to produce accuracy: parts that fit other parts (gauging), parts that are all the same (repeatability), or parts that have uniform surfaces (uniformity).

Despite its many tasks, the marking gauge is simple to build, yet has features that should not be overlooked: Pin shape, head shape and single-handed use.

With these features in mind, building your own gauge is easy. I’ll bet you can’t stop with just one. Make some out of your favorite exotic wood to avoid losing them in the pile of shavings you’re sure to make. PW

From the December 2006 issue #159
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