10-02-2023, 07:50 PM
(10-02-2023, 05:56 PM)Pete O Wrote: If I may be so brave as to disagree with Willie, on a simple gear train it doesn't matter how many idlers there are- one tooth moves one tooth all the way through the gear train so a 10-tooth drive gear will drive a 100-tooth driven gear at a 1:10 ratio no matter how many idlers are used to take up the distance between them, odd numbers of idlers reverse the rotation and even numbers correct it. (When I was 15 I had an exam question that showed a gear train with about 5 idlers, gave the input RPM and asked the final RPM, I spent ages figuring out every ratio across the train to come up with the final RPM- which was the same as the input RPM with the same gear size! Live and learn.) Different with compound gears like the drive gear at the top of your photo, two gears of different sizes on the same spindle alters the RPM.
Right you are Pete. When I see at a change gear set on a lathe I'm already thinking compound gear sets. But then again what's in my head and what comes out of my keyboard doesn't always line up anyway. Good catch. Off to find my dunce hat now...
Willie