View Full Version : P/A for South Bend change gears

10-04-2005, 12:55 PM
I searched the archives a bit, and found some interesting discussion/enlightenment about finding the specs for a gear, like pressure angle.

My problem is a relatively simple one. I finally have nearly everything I need to retrofit my South Bend 9 with a quick change box. Unfortunately, I need a 20T gear, which is not part of the old change gear set.

John Stevenson mentioned a while back that most machines use a P/A of 14 until WW2, then it was mostly 20 after. I believe my lathe was made in 1942.

Anybody know offhand what the P/A is for South Bend 9 change gears? Armed with this info, maybe I can pick one out of stock from someplace like Boston Gear.

Thanks, guys.


10-04-2005, 01:02 PM
Virutally positive it's 14 1/2.

10-04-2005, 01:43 PM
All you need is to get the same ratio. You should be able to do that with the change gears.

10-04-2005, 02:23 PM
Use the 16 tooth stud gear to drive the 32 tooth change gear. This gives a two to one ratio. You need a 2.8 to 1 for the QC gearbox. So make a compound gear with the 32 and the 40 tooth to drive the 56 on the gearbox input. The 40 driving the 56 is a 1.4 to 1 ratio. It will work much the same as my metric trick gear except in your case the ratio is exact. You may need to figure out an idler gear or two on the banjo.

See here on how to make the compound gear using your existing change gears. You should have it done in minutes.


10-04-2005, 10:02 PM
As always, you all come through in fine fashion. South Bend wants $64 for the 20T gear that actually goes with the machine. I figure if I go with that and eBay the old "manual change" set, it's a wash. Problem is, I'm sure if I do that, I'll need them. Now I see why. Thanks, Evan.