# South Bend feed rate

• posted
My circa 1930 SB 9" lathe w/single lever quick change gear box says that to
determine longitudinal feed rate to multiply the tpi by 3.25. When I
multiply 3.25 times 96 tpi I get 312. What does this number mean? As a
check, I multiplied 48 tpi by 3.25 and the number is 156, which is smaller
than for 96 tpi. Seems to me that 48 tpi should feed faster. Note: I am a
hobbyist and so far I just experiment to find the best feed rate, and have
found that 96 tpi works fine for mild steel. Thanks.
• posted
Jim, There is a gear reduction in the apron when engaging the lead screw with the feed clutch of 3.25 to 1 in comparison to directly engaging the lead screw with the half nut. South Bend means 1" / 96TPI / 3.25 = .003205 inches per spindle revolution. It's easy. You just have to learn to think South Bend. Good luck, Steve
> My circa 1930 SB 9" lathe w/single lever quick change gear box says that > to determine longitudinal feed rate to multiply the tpi by 3.25. When I > multiply 3.25 times 96 tpi I get 312. What does this number mean? As a > check, I multiplied 48 tpi by 3.25 and the number is 156, which is smaller > than for 96 tpi. Seems to me that 48 tpi should feed faster. Note: I am a > hobbyist and so far I just experiment to find the best feed rate, and have > found that 96 tpi works fine for mild steel. Thanks. > > >
• posted
TPI corresponds to turns/inch, feed is specified in inches/turn. The plate stops short of telling you that you need to take the reciprocal of TPI x 3.25 to get the carriage advance in inches per revolution of the spindle.
1 / 48 x 3.25 = .0064 in / rev 1 / 96 x 3.25 = .0032 in / rev
Ned Simmons
• posted
> Jim, > There is a gear reduction in the apron when engaging the lead screw with > the feed clutch of 3.25 to 1 in comparison to directly engaging the lead > screw with the half nut. South Bend means 1" / 96TPI / 3.25 = .003205 > inches per spindle revolution. It's easy. You just have to learn to think > South Bend. > Good luck, > Steve >
>> My circa 1930 SB 9" lathe w/single lever quick change gear box says that >> to determine longitudinal feed rate to multiply the tpi by 3.25. When I >> multiply 3.25 times 96 tpi I get 312. What does this number mean? As a >> check, I multiplied 48 tpi by 3.25 and the number is 156, which is >> smaller than for 96 tpi. Seems to me that 48 tpi should feed faster. >> Note: I am a hobbyist and so far I just experiment to find the best feed >> rate, and have found that 96 tpi works fine for mild steel. Thanks. >> >> >>
• posted
I see how to figure this now. Thanks for your timely reply.
Jim

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