Introduction: Versatile Router Mortising Jig
This is the latest incarnation of a mortising jig I have been developing over many years. It is fast, accurate, and I can cut identical parts repeatedly, all exactly the same. I can also use it for mortices in end-grain, so that I can use floating tenons if I want to. That makes angled M&Ts a whole lot easier. The jig consits of:
1. A top block which is clamped to the bench. I use holdfasts but you could also trap it between dogs. There is a groove at the back to restict the lateral movement of the router and a T-track in the top to accomodate travel stops.
2. A vertical front board against which the workpiece is clamped
3. A front block which supports the workpiece. It also has a T-track, which carries the positioning stop and two toggle clamps. This block can be adjusted up and down, or repositioned vertically, or at an angle, for end-grain mortising.
Step 1: Make the Top Block
The length of the top block depends slightly on how you plan to hold it, but mine is about 600 x 70 x 50mm
(24 x 2¾ x 2") long. It is fixed to a Base which is longer at each end so that it can be clamped down. Behind it is a gap and a retaining strip. These need to be sized to suit your particular router, but mine is a 10mm gap with a 600 x 20 x 20 retaining strip.
The router fence is fitted with an auxilliary face which protrudes downward so thet it rides in the groove. This keeps the router on the straight and narrow and stops it wandering.
A 3/4" T-Track is let into the top. It must be dead flush with the top surface - too high and the router will wobble.
Step 2: Make the Front Panel
The front panel has two vertical slots for the front block, with a rebate (rabbet) at the back to accommodate a flange nut. Mine is M8. The Imperial equivalent is 5/16".
There is a similar slot, but curved. This so that the front bed can be mounted for cutting end-grain mortices for floating tenon joinery.
The front panel is then screwed to the top block and base.
Step 3: Make the Front Block
The front block supports the workpiece. A pair of holes line up with the slots in the front panel so that it can be clamped with a pair of Bristol levers, with flange nut behind. There is enough play so that workpieces can be held at an angle, as you might for table legs, for example.
There is also a third hole which lines up with the curved slot in the front panel for end-grain work.
A T-track supports the positioning stop and a pair of toggle clamps.
You may have to chamfer the left hand end for end-grain work, if it impedes the travel of your router.
Step 4: Add the Clamps and Stops
The toggle clamps are attached to a small piece of steel, drilled and tapped to match. For horizonal work they can just be left easy in the T-track, but you will have to snug them up for vertical work. Depending on your particular toggle clamps, you may wish to modify the heads. Mine a pair of bottle-tops filled with hot glue!
The are two travel stops which ride in the top block and determine the length of the mortice. They have a rectangular key set into the underside. This allows the stop to slide nicely without wracking and stops it rotating in use.
There is another stop for the front block. This allows mutiple parts to be located in exactly the same position. The vertical slot allows me to use it with a piece of sacrificial scrap underneath the workpiece if I am cutting through mortices.
Step 5: Setup for Horizontal Mortising
Attach the front block to the front panel using a pair of Bristol levers and flange nuts.. Lay the workpiece on the block, with a sacrificial piece underneath if necessary, and adjust it all so that the workpiece is flush with the top and the working area is somewhere around the centre of the jig. Set the positioning stop in place and adjust the toggle clamps to fit the workpiece.
With the router fence inthe groove, adjust the lateral position to cut the mortice where you want it. I use a setting pin to help me but you can do it by eye.
Move the cutter to the front end of the block and set one of the travel stops, then do the sme at the rear end. Make sure that all you knobs and levers are secure.
Set the cutting depth and away you go!
Step 6: Setup for End-grain Mortising
The front bed can be mounted either vertically or swung at an angle for end-grain mortising. The toggle clamps will need to be snugged up otherwise they just drop onto the floor. The positioning stop goes underneath to support the workpiece.
Adjust the router and stops as before and cut the mortise.
Step 7: Done!
Enjoy the fruits of your labours.
If you have any queries, just ask and I'll try to help.
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