Gear Train for Two Tumbler Quick Change Gear Box

Hello,

I have been reading the forum for the last couple weeks. I have since joined so I can access all the info. here.

I have a South Bend Heavy 10 Collet lathe.

I have a simple question regarding the gear train from the spindle to the stud, to the idler, to the screw. Doesn't the actually number of teeth matter on each of these gears? For example, I know the stud gear is 20 for the majority of threads. But what about the idler. I have an 80 on it. I also have an 86. The book just states a "large gear in the idler" and a "small gear on the screw" (paraphrasing).

I am actually more interested in a super slow feed rate for a fine finish than cutting threads. It just seems one tooth more or less would affect the tpi and/or the feed rate.

Thanks, B-Fifty2

Stud and screw (input to gear box) gears are the functional tooth counts. Idler's only job is to connect the two. Any number of teeth as long as it is physically the right size to do this connecting job.

This all changes when the idler is a pair of gears (differing tooth counts, attached to each other), at which time the gear train is said to be COMPOUNDED

If you don't have this book, you need it and you need to know what is in it. On edit: I see on page 74 the 10" 1" collet machine goes down to 480 TPI - which means the lowest feed rate of any South Bend not fitted with special gears

http://campkahler.com/files/How_to_Run_a_Lathe_SB_1of2.pdf
http://campkahler.com/files/How_to_Run_a_Lathe_SB_2of2.pdf