This gauge uses purpleheart for the fence and quartersawn white oak for the shaft. Choose a hard wood that works easily without excessive chipping or tear out for the fence blank. After machining the blank, it is re-sawn and glued together to form the mortise for the shaft. Keep this in mind when selecting your wood and try to choose a species and cut that will hide the glue line when completed. The dense straight grain of purpleheart serves this purpose nicely.
The three pieces that make up the marking gauge are relatively small and working with small pieces on power tools raises additional safety issues. To reduce the risk, use a longer blank than necessary to machine the parts for the fence. This will enable you to make several gauges – a couple for yourself and several for gifts. You could alternatively make up a jig to hold the small pieces.
- Mill the fence blank (A) to be perfectly straight and square. Square up both ends at this time, the actual length is not crucial.
- Set up a 3/8″ Onsrud bit in a table mounted router. Place the fence so there is a 1/8″ gap between the bit and the cutter. Raise the cutter to project barely 1⁄16″ above the table. Use a feather board to maintain constant pressure down against the table and against the fence.
- Make one pass along the length of the board. There should be a 1/8″ strip of wood remaining at the edge of the piece. This is a runner that keeps the board level during subsequent passes.
- Move the fence back and make another pass. Keep doing this until the groove is 5/8″ wide.
- When the last pass has been completed, raise the bit to project 5⁄16″ from the top and make another pass.
- Move the fence 1/4″ toward the bit and make one more pass. This will result in a 5⁄16″ x 5/8″ groove running the length of the board.
- Use a table saw to rip the runner from the edge of the piece.
- Using a mitre saw or a cross cut sled on a table saw, cut the two pieces that make up the fence from the blank.
- Glue these two halves together to form the fence with a perfectly square mortise through the middle. Pay attention when applying the clamps – the glue acts as a lubricant and the parts will tend to shift.
- Drill a 1/8″ pilot hole through the fence over the compression gap.
- Counterbore one side to accept a 1/4-20 threaded insert. Drill only as deep as needed for the insert.
- From the other side, drill a clearance hole that will accept a 1/4″ threaded rod.
- Ease all of the corners around the perimeter of the fence, and even out any irregularity at the glue line. Ease the edges of the face slightly but leave the edges of the mortise as they are.