In article ,
GTO69RA4 wrote:
One threading chart, as ordered:

http://members.aol.com/gto69ra4/Photos/davis_chart.jpg

A little fuzzy but legible. This one reads a little differently than the newer
machines I'm familar with. Can you help my thick head out with decoding it? Not
having the lathe's complete gear train assembled doesn't help.

It is rather puzzling.

I would guess that the "NO" column represents the three
positions of the lever on the headstock.

Looking at the "cut" column, which I presume is the
thread-per-inch, and finding three that use the same gear in the "LE"
column, the ratios of the headstock lever are 1:1, 1:2 and 1:4.

The note "User 16 gear to compound" may refer to the tumbler for
forward/reverse for the threading train, and a 32 tooth gear on a common
bushing with the 16 tooth gear.

The LE. column is a gear mounted on the leadscrew at a guess.
It looks as though the smallest vs the largest gear on that has a ratio
of diameters of 2.5:1.

They seem to use the "2" position and a 64-tooth gear, instead
of the alternative of the "3" position and a 32-tooth gear to get 16
TPI, probably because it is easier to get torque into the leadscrew with
a larger gear.

Probably someone could take the time to calculate the proper
geartrain if you told them the thread pitch of the leadscrew, and the
number of teeth on the gears on the spindle and the reverse tumbler
assembly.

An end-on photo of the headstock would help by showing the "harp"
on which the gears mount, and show whether there is enough other stuff
there to help figure things out.

A pretty good range of threads, though there are relatively
uncommon threads which would take some more game playing with the extra
gears, such as 27 TPI, and you seem to not have anything over 40 TPI.

Good Luck,
DoN.
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