A Finger Joint Jig for the Router Table

The author doesn’t get his fingers burnt with his latest router jointing jig

a jig and hose
A safe and easy to use jig for router tables

Finger joints are an excellent means of making small boxes, and a router in a table is a good way of cutting the joints. There are commercially available jigs for this, but like most of the workshop made ones I have seen, they mostly lack any form of guarding for the exposed cutter. I cannot see where my fingers are in relation to the cutter from behind the jig, so I wanted to make something that would be much safer, and also incorporate a facility for extraction. This design draws on ideas from many other jigs I have seen, and combines those ideas to make what I consider to be a safe, easy-to-use and effective jig. The jig is designed to fit my router table that was described in Woodworking Crafts, issue 13, and to cut 12mm fingers. It could easily be modified to fit any commercial or user-built table and altered to suit different sized finger joints.

Things you will need

  • 10mm and 18mm MDF
  • 2 x oak strips – 1 @ 20 x 20mm – 1 to be cut and planed
  • Sharp bevel edged chisel
  • Drill
  • Mounting screws
  • Clamps
  • Router cutter
  • Extractor or vacuum
  • PPE
  • Glue
a plan for a joint
Exploded view of the fence

Making the base

sheets and strips of wood
Start by making the base. The main components for the base are a sheet of 10mm MDF and two oak strips, one 20 x 20mm. These run against the edge of the table, the other cut and planed to run smoothly in the mitre slot of my table
Two strips of wood on a board of MDF
Pre-drill the strips to avoid splitting when screwing. Drill and countersink both of the oak strips at three points to accept the mounting screws and clear up any breakout at the exit holes with a sharp bevel edged chisel.
A drill driving a screw into pieces of wood
With the edge strip temporarily clamped to the top surface of the MDF board, carefully align the mitre slot strip and screw it to the bottom of the board. Flip the board over and, with the mitre slot strip located in the slot, clamp the edge strip to its correct position on the bottom of the board
clamps holding down pieces of wood whilst being drilled
Next, flip the board back over again, with the strip still clamped to it ready to be screwed into its final position
a handle sticking out of a piece of wood
Fit the router cutter that will be used to cut the fingers to the table and use it to cut its own slot in the base of the jig. Begin with the cutter just below the surface
a man turning a handle over a piece of wood
Adjusting the height of the router cutter. Carefully position and align the jig base and then, holding down the board with your hands well clear of the cutter area, raise the cutter through the board to begin the cut
hoovering up dust from a piece of wood
Complete the cut by sliding the base against the cutter until the slot is the length you require. Use an extractor or vacuum to collect the dust and always wear suitable respiratory protection when working with MDF

The fence

The fence is made using two 18mm MDF boards, biscuit jointed together. Take care to cut these square and be sure to make the biscuit joints as accurately as possible.

biscuits in pieces of MDF

Any inaccuracies will be compounded when it is used to make joints.

gluing a piece of wood using a right angle
Glue and clamp the fence components together carefully, checking for square, then leave it overnight to set completely before moving on to the next step
Pieces of wood at various angles
Once dry, screw and glue the hardwood support blocks in place to give added strength to the fence, to keep it square against the forces that will be applied when cutting. Carry out a final check to make sure everything is square and true
a large piece of wood which is MDF
The fence must be fitted to the base absolutely dead square to the cutter slot, or inaccurate joints will result. Squareness is facilitated by cutting a peg to fit exactly into the width of the slot. This peg will also be used to form part of the jig so its thickness should be just slightly less than the thinnest boards you intend to use in your finger joint projects. The fit of the width in the slot is critical so cut slightly oversize and plane down until a perfect fit is achieved.
clamps and pieces of wood with a hoover in the corner
With the peg located in the slot use a square to accurately position the fence, then clamp to the base. Take great care at this stage to achieve perfect alignment with the slot
clamps holding wood together, and a drill and screw
Once accurately clamped, turn over the assembly and attach the fence to the base by means of countersunk screws. Make sure the countersinks are deep enough so that the screw heads are just below the surface to enable the jig to slide freely
various pieces of hardware
Use a piece of plywood or MDF, with two 8mm wide slots to take a dowel and the mounting bolt, to make the guard and extractor assembly. Use a Forstner bit to cut a hole for the extractor outlet and screw the extractor port, which was made by cutting the end from stepped hose adaptor, over the outlet hole

Using the jig

a handle coming out of a piece of wood
To use the jig, fit an appropriately sized cutter in the router collet and adjust so the cutting height is equal to the thickness of the jig base, plus the material that is to be used
a set up jig
Hold or clamp the workpiece against the fence with the edge butted up against the peg and run the jig through the cutter to make the first finger slot. Then position the first slot over the peg and cut the second slot. Repeat this process until all of the slots are cut
a man holding together pieces of wood on a jig
To achieve a perfect fit, position the last notch of the first workpiece over the peg and butt the second workpiece against it and cut the first notch in the second workpiece. Then continue as for the first piece to cut the remainder of the slots
two pieces of wood at right angle
The result should be a perfect fitting joint, every time

Summary

And there you have it. A jig that enables you to make accurate joints whilst keeping your hands well away from the dangerous parts. Of course, diligence is required when working with any tools, so don’t become complacent whilst working with the jig.

Further reading

Words: Walter Hall

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