WoodSkills Issue 02 - Page 53

The mortise is bored down 3/4 inches, the thickness of the nut. All that remains is to chisel out the wood forming the outline of each six-sided nut. If you do not have access to a drill press, use a drilling guide. A drilling guide is a tall block of wood with a 3/4-inch diameter hole drilled vertically through. The hole must be perpendicular to the face of the drilling guide. The guide is clamped to the jaw surface and a Forstner bit and drill are used to bore a 3/4-inch diameter hole. I use this technique to bore holes in workbench tops since the top is too large to place on a drill press table. It is critical to mortise the six-sided nut into the rear jaw to slightly below the level of the surface. This keeps the nut from interfering with clamping operations. Some trial and error is involved in creating the mortise deep enough. A small ruler fit into the mortise can be used to determine the depth and wood left to remove. Bevel-edge and mortise chisels were used to clean the mortise out. Since the jaws are hard maple, mortise chisels excel at this operation. With softer wood, I might get away with using only bevel-edge chisels.

Bevel-edge chisels were used to outline the cut and heavier mortise chisels removed the waste. This step is tedious, but the results are worth it. Having the nut completely housed is aesthetically pleasing and strong. The alternative is to create a square mortise nut and fit the nut into the mortise. This procedure is outlined in the Benchcrafted instructions. In this photo, a cleaned up mortise is seen, as well as a mortise chisel used to hog wood out. There is trial and error in fitting the large six-sided nut to the mortise since it needs to sit below the face of the rear jaw. This operation is performed on both screw holes in the rear jaw. The recommended width of the front and rear jaws was gleaned from Benchcrafted instructions. The instructions call for a rear jaw width of 5 1/2 inches and a front jaw width of 5 5/8 inches. The extra 1/8-inch width of the front jaw allows it to overhang the edge of the workbench for alignment. The distance from the center of each screw hole to the top and outside edge of rear or fixed jaw is:

2.75 inches from top (1/2 of the width of the jaw itself @ 5.5 inches)

3.5 inches from outside edge (allows for handwheel to fit within edges)

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Mortise for captive six-sided nut created using bevel-edge and mortise chisels