Shop-Made Mortising Jig
by Dan Phalen
Scappoose, Oregon - October 2010—While building my Mission Cabinet, I discovered a need for a mortising jig to rout the leg mortises. Here's what I built, with a few custom features in order to take advantage of jig fixtures and hardware I already had. It's not real pretty, but it does the job accurately and efficiently.
Plans available NOW!
Jig Body
Let's start with the body, a simple 16" x 6 1/2" box with the base extended to either side a couple of inches for bench clamps.
I used simple shelf straps from the hardware store for my runners, and dadoed grooves in the underside of the table to allow front-to-back adjustment for router bit positioning.
Here's a view of the backside of the front plate, showing four of the eight 5/16" T-nuts inserted into countersunk holes. These T-nuts accept the 5/16" knobs that tighten the hold-down system.
The hole pattern for the 5/16" T-nuts in the Front plate.
Table
The table is a piece of 12" x 16" x 3/4" shop ply. The groove for the router base is 1/4" deep, but its width depends on your particular router base diameter.
My DW616 has a flattened side to follow straight edges like this, so my groove width is 5 1/2" offset from the front by about 1-1/4".
The sliding stops are made from 1/4" hardboard. They are fastened to the table with 1/4" threaded knobs that screw into 1/4" T-nuts embedded in the table's underside. Each stop is slotted to permit right-left adjustment for alignment with the workpiece mortise marks.
Making Mortises
First mark the workpiece to indicate the centerline for the mortise and the ends where the tenon shoulder fits.
Next, drill a hole at each end of the mortise to the mortise depth using a drill press or a handheld power drill. This step will help you guide the router bit for setting the left and right stops.
Place the piece in the jig and shove the hold-down plate upward until the workpiece fits tight against the table underside. Lock it in place with the rubber-tipped hold-down.
Positioning right-to-left and centering the bit depend on (a) the size and shape of your workpiece, and (b) your drill bit diameter and router base shape.
Now you're ready to adjust the stops so that the router base touches each stop without moving the bit beyond the mortise top and bottom
Always use a plunge router with depth stops so you can cut the mortise depth in increments.
Conclusion
This mortise jig has become one of my primary go-to tools in the shop. Easy to build, simple and straightforward setup. Be sure to download MY PLANS.
Thanks for looking and I hope you enjoyed your visit.
Questions or comments?
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