Making and Using a Finger Joint Jig for the Router Table
Walter Hall doesn’t get his fingers burnt with his latest router jointing jig
Walter Hall doesn’t get his fingers burnt with his latest router jointing jig
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, but 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
Making the jig
1. 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, to run against the edge of the table, the other cut and planed to run smoothly in the mitre slot of my table
2. 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
3. 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
4. Next, flip the board back over again, with the strip still clamped to it ready to be screwed into its final position
5. 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
6. 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
7. 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
8. 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. Any inaccuracies will be compounded when it is used to make joints
9. 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
10. 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
11. 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
12. 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
13. 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
14. 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
1. 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
2. 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
3. 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.
4. The result should be a perfect fitting joint every time
