This jig is used to cut open bridle-joint mortises in frame members. It solves many of the problems inherent with sliding jigs, which tend to be complicated to make and adjust, and sometimes wobble during the cut. The only disadvantage is that the jig leaves a slight concavity at the bottom of the mortise, as shown in the sketch. This space doesn’t show in the finished joint, however, and since it’s end grain, the missing wood isn’t critical to joint strength.

Make the jig by screwing a hardwood fence to an 8-in. wide piece of 3/4-in. plywood. Clamp the jig to the rip fence so that the frame member to be mortised will be centered over the saw arbor. Adjust the rip fence so that the sawblade is the proper cheek thickness from the jig.

To cut the mortise, hold the workpiece firmly against the plywood, with its back edge tight to the hardwood fence. Plunge the work down the fence onto the blade. Draw it up, flip it and cut the other cheek. On narrow stock, this will complete the mortise. For wider stock, chisel out the waste.

Frederick J. Miller, Chatsworth, Ont., Canada

Fine Woodworking Magazine, December 1984 No. 49

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