Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hi Jim and Stoker,
The shouldered disc that the template is screwed to is free to turn on the shaft. It has 2 holes in it that align with the 2 rows of holes in the index plates. The index plate is secured to the shaft with a set screw. In operation the pin is placed in the first hole, the shaft is now secured to the helical template. The shaft is moved forward until the template contacts the bearing. Now by keeping forward pressure on the shaft, to keep the template against the roller wheel, the shaft is rolled against the template creating the helical motion. On the return stroke the same pressure is held against the roller wheel so the cutter tracks in the same cut.
Once returned to the start position the pin is pulled out and moved to the next index hole and the template disc is rotated until the pin drops into the corresponding hole then the procedure starts again.

As far as gear tooth cutters go most of my gears are no larger than 48 diametral pitch. That means the gear has 48 teeth per inch of diameter. The module formula is m=25.4\DP. Involute cutters come in sets of 8. This covers the proper gear tooth form from rack to infinity. A rack gear has a straight sided tooth with an angle corresponding to the pressure angle of the gear, 14.5 or 20 degrees. As the gears get smaller the involute curvature of the tooth gets more circular.
I only have a couple of commercially made involute cutters. These are 48 DP. I usually make up my own 'hob style' cutters for most of my gear cutting. I have made cutter all the way down to 80 DP. I draw the gear tooth form in my CAD program then take the dimensions and make a gear cutter from drill rod and harden it.
When cutting a particular spur gear, lets say it has 1.00" D.P. and has 48 teeth. You would use a #3- 48 DP cutter which will cut from 35-54 teeth. When cutting a helical gear with the same diameter and D.P. you would use a different numbered cutter due to the math in calculating the proper tooth spacing of the gear. There are charts that show how to calculate which cutter to use.
I hope this explains both questions.
gbritnell