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Finger Joint Jigs


Plate 1. Matthias Wandel's screw advance box joint jig.


Obsession


I think Matthias Wandel has to take full responsibility for the weeks I've spent trying to perfect a finger joint jig. What a wonderful machine. But of course I must improve it!

There were two issues Mr Wandel pointed out. First was play in the gears. He solved this with a spring I believe. The second issue was it took a long time to return the carriage to the start position. I think he solved that too with some cool gears.

But everything can be improved, or at least I like to try.

All these jigs are for my Delta bench top table saw.

Plate 2. Typewriter carriage.


Typewriter Carriage


The rack and pinion gear off a typewriter would advance a bit at a time and be repeatable. Solved the play and quick return issues, just as it did for typing.

Trouble is the amount of space the gear advanced was not the same as the saw blade width. So I abandoned the typewriter carriage.

Plate 3. Prototype I.


Hard Index Prototype


index

Plate 4.

Rectangle spacers of ¼" aluminum, drilled in the center and strung on ¼" threaded rod. The rectangles can be flipped up or down to make a the rack part of a rack and pinion gear, the stylus would be the pinion.

This worked well. The width of the spacers and saw blade had to be exactly the same. I mounted 2 blades onto my saw to get the ¼" width. This is not something the manufacturer suggests, but it seemed "safe", as if table saws could some how be "safe".

This setup allowed just one finger pattern, but that was probably OK as it is the classic pattern. But the stylus had to be tight in between the spacers which made moving the carriage for each cut difficult and I assumed the spacers would wear.

Now I saw the "gears" weren't really needed at all.

Plate 5.


Paper Index Prototype


stylus

Plate 6.

Instead of aluminum spacers I could just amount a piece of paper to the fence with the cut pattern. Line up the stylus, lock the carriage, make the cut and repeat.

Worked OK. I wanted to improve the stylus. I kept forgetting which side of blade it represented.

I also had a problem with the blades cutting at slightly different depths. It made jagged bottoms instead of nice square flat bottoms.

Plate 7.


Final (For Now)


This set up uses a single saw blade to get a flatter bottom. I move the stylus to nibble away joints. Fingers can be in any thickness, or any pattern.

The single blade made flatter bottoms but they aren't perfectly flat. Probably good enough for most jobs, but I'm still thinking of improvements.

I also added a magnifying glass so I could really line up the stylus perfectly. This is not a very mechanical process. Where you position relative to the line results in tighter or looser joints. Tight is good for solid wood, looser is better for plywoods as the cross grain plies in fingers can fall apart if too tight.

The reddish brown piece locks into position so it can be removed for storage.

The entire carriage rides on top of a normal table saw sled. Once the carriage is moved left or right and locked down the sled is pushed forward to make the cut.

Plate 8.


Magnification


The stylus is machined to the exact thickness of the blade. When the carriage is moved all the way to the right and the blade hits the side of the carriage it means the blade is at the edge of the wood to be cut. The pattern can then be moved under the the stylus to whatever pattern I want to cut.

The magnifying glass has a small part that is higher magnification. I use the large field to do rough position and the higer magnification to fine tune. And the higher magnification is directly above so my sight line has to be just about the same each time to see the stylus.

I mounted a small LED flashlight to eliminate shadows cast by the stylus.

Plate 9. Door handle.


Door Handles Are Handy


I've spent a lot of time over the years making handles for jigs. The handle in Plate 5 is one such crude handle.

I recently stumbled into using old door handles. These old handles have a square opening for a shaft. ⅜" threaded rod, which is fairly inexpensive, can be ground down to fit into that sqaure opening. A set screw or riviet can hold the rod in place. Great handle. Looks and feels nice. I also use cabinet knobs when a smaller knob is needed.

Plate 10.


Clamp to Hold Pieces


A board in the middle of the carriage is where the work pieces are clamped. It's in the middle so the blade doesn't cut through the front of the jig.