Synopsis: Create mortises with a plunge router with this universal jig by Philip Morley. The jig’s top moves in and out on runners, which makes positioning the mortises easy, and knobs lock down the top at the desired setting. A pair of sliding stops built into the top make it simple to set the length of a mortise.
I designed this jig as an affordable and accurate way to create mortises with a plunge router, usually for slip-tenon construction. Because it uses a guide-bushing system, the jig is universal—it’s not specific to any particular router. The jig’s vertical front panel has a grid of dovetailed grooves to accept MatchFit clamps, so you can clamp the workpiece anywhere on it easily and securely.
The jig’s top moves in and out on runners, which makes positioning the mortises easy, and knobs lock down the top at the desired setting. A pair of sliding stops built into the top make it simple to set the length of a mortise. I create spacers for commonly used mortise lengths so I can set the stops quickly with no measuring. Centerlines on the spacers, the top of the jig, and the stops make setup simple, and make it easy to repeat setups precisely.
I use a 5 ⁄ 8-in. OD guide bushing and choose bits with enough extra length to compensate for the 3 ⁄ 4-in. thickness of the jig’s top. I find I get the best results using a 1 ⁄ 2-in.-dia. bit, or a 3 ⁄ 8-in.-dia. bit with a 3 ⁄ 8-in. shank.
Built with Baltic-birch plywood (except for its hardwood runners) and assembled with butt joints and screws, the jig is quick to make yet rigid and durable. Designed to be used with guide bushings, it can accommodate virtually any style of plunge router.
Microjig MatchFit Dovetail Fixture and Jig Clamps - 2 Piece
- Clamp Throat Depth: 2-3/8" - Clamp Capacity: 0 to 5-1/4" - Clamp Pressure: 595 lb. open at 4" - Minimum Dovetail Slot Length: 3-3/4" - Dovetail Profile for Clamp: 1/2" x 14°
Price: $45.00 at the time of writing
A sturdy base
Top of the jig
Most of the jig’s critical machining is in the top, and it occurs at the router table. In preparation for that routing, be certain to saw out the top so its ends are perfectly parallel to each other and square to the front edge. Any error here will directly affect the accuracy of the jig.
Bottom view of top
Twin slots in the top
To accommodate front-to-back adjustment of the top, rout two stopped slots for the threaded studs. At the router table, with a 5 ⁄ 16-in.-dia. spiral bit, cut the slots in several passes between a pair of stop blocks, lowering the workpiece onto the bit at the beginning of the pass and lifting it off at the end.
Single slot for the bushing
Use a 5 ⁄ 8-in. spiral bit to rout a stopped slot for the guide bushing. As with the adjuster slots, use stop blocks and make a plunge cut in stages.
Make ways for the runners
Cut 3 ⁄ 4-in.-wide throughdadoes in the underside of the top to accept the runners attached to the subtop.
Fix the runners to the subtop
After counterboring and through-drilling the runners at the drill press, Morley attaches them to the subtop with pan-head screws. To locate the runners perfectly for screwing, he sets them in their dadoes in the top, applies double-sided tape to their exposed face, and sets the subtop in place, being sure the top and subtop ends and front edges are flush.
The front panel gets dovetail slots to accept MatchFit clamps. You’ll be clamping your workpieces to this surface, so be sure the piece of plywood you select for it is completely flat.
Philip Morley works wood in Wimberley, Texas. He is a lead teacher and co-owner at the Austin School of Furniture.
For more information and photos, please click the View PDF button below.
From Fine woodworking #301
More from Philip Morley
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It’s in the Details
Philip Morley discusses subtle details that some clients may not notice or appreciate. They take the most time and make it harder to make a living at woodworking, but he can’t help himself.
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Philip Morley’s small wall cabinet has sides that curve inward at the top, with an asymmetrical arrangement of drawers, door, and open shelves.
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