1. Home
  2. ⏣ General Metalworking
  3. South Bend feed rate

South Bend feed rate

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.

Reply to
Jim and Jackie Instone
Loading thread data ...

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

Reply to
Steve Lusardi

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

Reply to
Ned Simmons

Reply to
Jim and Jackie Instone

I see how to figure this now. Thanks for your timely reply.

Jim

Reply to
Jim and Jackie Instone

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.