ADJUSTABLE MORTISING JIG
Modification of a Woodsmith plan.
SHOP OWNER: Yair Feldmann
LOCATION: Raanana, Israel
Only after completing the Adjustable Mortising Jig (Woodsmith No. 147, June 2003), did I realize the following problem: since the total length of my standard cutting bit is about 2” and the top of the jig is ¾-inch plywood, the depth of the mortises I can produce is very limited! Add to this that about ¾-inch of the bit is “stolen” by the shank inside the collet plus another ¼-inch by the Plexiglas router base of the jig, and you see my problem.
I solved the problem by changing the way the router is held in place, while still making use of the jig's base and main idea. My router is a Black & Decker KW800 plunge router, and I assume you can do the same with other brands and models as well.
First, I built a hardwood frame as you can see in the pictures. In the lower (closer to me) part of the frame, on both sides, I drilled two holes and inserted two metal rods – originally the rods of the edge-guide of the router. These rods enable perfect and smooth travel of the router sliding right, and left. If I want to use the router without the jig, I simply pull the rods out from the frame, and the router is easily released.
I added two pieces of a plastic ruler (one from each side of the frame) to determine the offset of the mortise from the zero point, corresponding with the face of the stock to be mortised. I attached a third ruler to the center cleat of the frame, so I can determine the length of the mortise, either by watching the ruler while mortising, or by clamping a small piece of wood at the desired point to stop the router on its travel from left to right.
To mortise, I simply clamp the stock, set the bit's depth, set the distance of the mortise from the stock face, tighten the frame with the four studded knobs, determine the travel of the router and here I go!. . . Yair Feldmann
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