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Mortising is a good job for a plunge router with electronic speed control. You can slow down the bit to compensate for the low feed rates that mortising generally entails. And that will prolong the life of the bit you use.

Mortising can be really hard on bits. Wood is a surprisingly good insulator. The heat generated as the bit cuts a mortise isn't dissipated through the material; it's retained in that confined pocket. The danger here isn't burning of the wood so much as dulling of the cutter. Bum marks are going to be concealed inside the joint, but a dull cutter hampers your ability ro even make the joint.

Mortises aren't very long, but they usually are deep. It Is hard to both plunge the bit and move it back and forth quickly. Heat builds up.

The alternative is to slow the bit down. Try running the router at about 15.000 rpm. It won't really affect the practical cutting rate, but it'll be easier on your hit.

A dandy way to mortise legs is in this trough like fixture. The fixture is held in a vise, and it in turn holds the leg. A stop clamped at the end of the trough helps you position each leg without a lot of to-do. The router's edge guide locales the mortise. And stops screwcd to the bach keep you from inadvertently routing loo long a mortise.

locate stw»5 equidistant from the centerline mark. the space. between them should equal the length of the rooter's edm. guide plus the mortise's length.

CLAMP THI5 TROUGH-STYLE. MORTISING FIXTURE. IN YOUR WORKBENCH VISE.

bottom locate stw»5 equidistant from the centerline mark. the space. between them should equal the length of the rooter's edm. guide plus the mortise's length.

AUWi this mark.

CLAMP THI5 TROUGH-STYLE. MORTISING FIXTURE. IN YOUR WORKBENCH VISE.

bottom

Cutting Angled Mortises
Simply by staggering the height of the fixture's sides, you can tilt the router without sacrificing its stability, so you can rout angled mortises. The edge guide references the taller side to position the mortise, but also to keep the router from skidding off thejig.

The construction of the fixture should be evident from looking at Trough-Style Mortising Fixture. It's a good idea to assemble it with screws—no glue—so you can replace one of the sides for cutting angled mortises.

Template Systems

Using a template to guide and con-irol a mortising operation has several advantages. It isn't the ideal approach for ever)' mortise, but there are occasions when it is absolutely the best.

The major disadvantage is that the template thickness steals depth from the mortise. If the maximum depth you can achieve with a particular bit is W: inches, then using a '/i-inch-thick template reduces the achievable depth to 1 inch. Obvi ously, you'll want to use the thinnest template material you can for this application.

So what arc the advantages? You can cut moniscs of a consistent length and width, without fiddling with edge guides. If you arc mortising narrow stock, the template itself can provide support for the router, and it can serve as a clamping base for the workpiece. With a template, you can rout mortises that are wider than the bit diameter. You can rout aesthetically pleasing through mortises of the sort you'd use in a plank bench.

The chapter "Template-Guided Work" has all the details on the best materials to use for templates, on scaling them to use with guide bushings, and so on. For mort ising, given that you want to conserve as much of the depth capacity as possible, use 'A-inch hardboard or plywood for the template. If the guide bushing's collar is less than '/«inch high, you can get by with '/e-inch material for the template if you apply strips of ^-inch stock around t he edges to reinforce it. In any case, cut the tem-

A through mortise can be template-guided. Use the crossing centerlines on the template to align it with similar lines on the workpiece. After the router work is completed, square the mortise comers with <a chisel.

TABLE ROUTED MORTISES

plate blank so it's three or four limes longer and wider than the moriise.

Workout the dimensions of the mortise you want, then bump it up to the size of the template opening that's necessary, given the bit and guide bushing you'll be using. In mortising operations, it's a good idea to use a large-diameter bushing so that the chips augercd out of the mortise can escape through the gap between bit and bushing. To bump up the mortise size to template size, subtract the diameter of the bit from the outside diameter of the bushing and add the difference to both the length and width of the monise.

Lay out the template opening on the template blank. As you lay out the opening, scribe indelible cen-teriines through the length and width of the opening, extending them well beyond the opening. These will later help you align the template for a monising cut. Routing is probably the cleanest way to make the opening. You can use a T-square with stops to control this cut.

To use the template, you simply clamp it to the work. Use a plunge router, the appropriate guide bushing, and, of course, an upcut spiral bit to make the cut.

If the mortise isn't too deep and the workpieccs aren't too hig and heavy, you can ma he an oversized template from '/2-inch plywood. Screw a locating cleat to the underside of the template, and clamp the template to the router bench, as shown. Clamp the work against the cleat, and rout. Here, a ¡wsi-tioning block is clamped to the cleat and a Vise-Crip C-clamp is used to clamp the walnut workpiece in place.

How you position and clamp the template depends a lot on the nature of the workpiece. If you arc monising narrow frame members, glue and screw a cleat to the underside of the template to both position the template and provide clamping surface. If you are monising a bench scat, you can align the ccntcrlines of the template with matching center-lines scribed on the workpiece, and simply clamp the template to the work. In most situations, double-sided carpet tape will do a good job of holding the template in place.

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