Further thoughts Peter,

Assuming you have an 8 tpi leadscrew, and you can set up the outside gearing for the constant pi (3.142) you can then use the gearbox as direct reading in DP,. ie 20 tpi becomes 20 DP. If your leadscrew is 4 tpi then the gearing should be halved and a leadscrew of 6 tpi would need similar factoring.by 1.333.

An approximation would be using driver 55 to driven 35 ( pi divided by 2) and a second stage of driver twice the driven will give you the overall gearing ratio for pi.

Again, the errors are small and probably negligible over limited engagement.

I would check it out with a grazing cut before deeper cutting to confirm you are getting what you hope for!

Regards Brian.

Another thought Peter,

Staying with the pi divided by 2 approximation above , but ignoring the second multiplier stage, you could then set the gearbox to 10 tpi instead and still generate 20 DP.

It is the method Myford use for their gearbox ML7; the simplicity appeals to me and you have the entire range of the gearbox to make DP worms in all the other pitches as well if you were so minded..

Good luck in your contruction, a little different to the others using 40:1 gearing..

Best wishes Brian

Hello Peter,

The pi divided by 2 approach has the smaller error of 0.04% , over 50 turns it is a factor of 6 times more accurate than compared to a 4 mm pitch worm.

If you have the gears there are better approximations of pi than 22/7 which is what the 55/35 [ 11/7] gear ratio is based on.

I don't know what gears you have available, I could give you some better approximations with that information.

email me wood_y [at] btinternet.com all lower case, no spaces.

Regards Brian