Graphical Construction Glossary >> Tools. >> Hand Tools >> Mortise Gauge

Mortise Gauge

A joinery tool for marking mortise joints or similar parallel lines. It has two adjustable gauge points on one side an a single gauge point on the other side of the main bar.

A typical hardwood and brass mortice gauge Photo thanks to Wikimedia Commons, User: asant

Used for marking any parallel lines, and in particular of course mortises.

• The width of the mortise is always set first. If the mortise is to be cut by hand, then use the same chisel held close to the gauge points to set the gauge, using the finger screw at the bottom of the beam.
• If you are going to be marking out a door edge for a mortise lock then use first the lock itself (with a touch of clearance) to set the width of the mortise, then use the face plate of the lock to set the gauge, (this time exactly) for the faceplate cut out.
• When the mortise width has been set nip the big locking screw up approximately in the right very lightly.
• Using thumb pressure on either side of the gauge body and checking from both sides of the stock (wood) the gauge is then set dead central to the stock.

Most of these mortise gauges have a single gauge point on the opposite side of the beam, but don't make the mistake of thinking this one tool will do the job of a marking gauge as well. It will but a separate marking gauge is essential. Invariably you will have the mortise one set up and not want to disturb the setting.

The gauge above is identical to the one that I bought as an apprentice joiner in the late 1950's, (as far as memory goes ;-). Some types have a knurled brass thumbscrew instead of the old slotted screw head seen here to lock the gauge. The screw head means that a screwdriver has to be found to adjust it, the screw slots get worn and because they had a large slot it meant that a large screwdriver was needed. This quite often lead to over tightening and damage to the gauge itself.

Rosewood was the wood of choice for quality tools and beech was used for cheaper ones.

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