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SB Thread Dial Questions

kdtop3

Plastic
Joined
Jan 30, 2021
Location
Tennessee, USA
Hey All,

I am refurbishing a 1935 SB lathe with 15" swing and 6 ft bed. Link below. I have been told it is a model N and was given this link to an old catelog: http://www.wswells.com/data/bulletin/bulletin_100/bl_100.pdf

I have just realized that it is missing its threading dial. :(

I am away from my shop, and I would actually measure before proceeding, but a table in the above manual seems to indicate that the lead screw is 1 1/8" diameter and 6 threads/inch.


Ebay has many 3D printed threading dials, but they don't seem correct for my model.

Questions:

1) How do I figure out the geometry of the setup? Specifically, how many teeth does the engagement gear need? And how many divisions on the display dial?

2) Are there tables that tell how to use the dial? Where I trained, the lathe had a sticker with a table that told things like (making this up off the top of my head): If threading 2,4,6,8,12,16,32 TPI, then start at any mark. But if 3,6,9,15 TPI then start on even marks, and so on. I am guessing the exact details of relationship between the threaded TPI and the thread dial is given by some formula. Does anyone know how to figure this out?

3) Does anyone know if there are drawings of SB lathes with dimensions etc that might give some better information?

Thanks in advance
Kevin (KST)


Here is a link to playlist of my restoration episodes:
South Bend Lathe Restoration - YouTube
 








 
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