# Poor man's Rotary index jig



## Gaffboat (Mar 11, 2012)

I needed to drill holes around the edge of a circle as part of making small gears for an automaton project I'm working on and lining up each hole by hand was a pain.

While thinking about a better way, I spotted a wooden disk that was waste from an earlier project and realized it was the simple answer. It was cut from 3/4" (19mm) stock, was about 3" in diameter and already had a 1/4" (6mm) hole in the center. 

I used a scrap of 3/4" x 4" pine as a base and drilled a hole for a 1/4" dowel which is used as a spindle to mount the disk so it rotates freely on the spindle. The gear blank is attached to the disk after it is also mounted on the spindle. A registration line is drawn on the base from the spindle center.

On my PC I generated 3/4" wide strips of paper with reference marks equal to the number of teeth for each gear I needed. (see photo 1) When the strips were cut out, I attached them to the circumference of the disk with a bit of tape.

Paper templates were glued to the 1/4" birch ply being used for the gears and a 1/4" hole drilled in the center of the template. Photo 2 shows all the parts ready to be a assembled on the base and spindle. When the disk / index is and gear blank are mounted on the spindle and lined up for the first hole, the jig is just clamped to the drill press table.

Then the disk is rotated from index line to index line (photo 3). A hole is drilled when each index mark lines up with the registration line on the base. Photo 4 shows a gear blank with all the holes drilled and the final photo (5) shows the finished gears. One was made with 8 teeth, one with 10, and a larger partial gear would have 40 teeth if it were a complete circle.

A simple no-cost jig that gave me repeatable, consistently spaced holes in a circular layout with little effort.


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## harrysin (Jan 15, 2007)

Excellent as far as it goes Oliver but what happened to the shots showing HOW you routed the teeth?


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## Gaffboat (Mar 11, 2012)

harrysin said:


> Excellent as far as it goes Oliver but what happened to the shots showing HOW you routed the teeth?


Sorry Harry, I should have been more clear. This was a drill press and bandsaw operation (you can just see the drill bit in the top of the third photo in the original post). So far on this project, I have only used the router to cut a guide slot in the rack part of the rack and pinion drive. That was done with a plunge router and a template setup I learned from you. :yes4:


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## harrysin (Jan 15, 2007)

Now I fully understand thank you Oliver, and I even more reckon that you have done a really excellent job. It demonstrates that necessity really is the mother of invention.


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