Posted by Nick Kempley on January 16, 2023 at 09:59:52:

Much is made of machine constants as if they are a mystery. They are not; they are readily determined, as I found out when I acquired an old RS00.

First I used a handheld tacho to measure the hob shaft speed and then the input shaft to the index gears. This gave a ratio of 3:1. The count the numbers of turns of the index gear output shaft to one turn of the work piece, in my case 36. This gives the basic machine constant as 12 (36/3).

By comparing different equations for the differential ratio with different types of gear pitch (PD, MOD, etc.) in became clear that this is not a separate number, but simply requires the gear pitch to be expressed in teeth per millimetre of pitch circumference. So instead of a 6 digit decimal constant for DP gears you use the basic constant divided by pi times 25.4. If like my RS00 your machine doubles the constant when then differential is engaged, then it is doubled for both indexing and the differential gear calculation, so 12 becomes 24. For MOD gears use MOD times pi as the division of constant times sin.

I hope my findings prove of use to other acquires of undocumented machines.

Nick