Change gears charts for inch threading on the 7x mini-lathe

Charts show gears combination and error %. In order to make inch threads on a mini-lathe with a metric leadscrew, additional 21, 55, 57 and 65 teeth gears are needed.

To calculate change-gears combination for inch threading on a lathe with imperial leadscrew you can use the following formula:
Thread Picth = Leadscrew Pitch (TPI) / ((A/B) x (C/D))

Change gears charts for metric threading on the 7x mini-lathe

Inch threading on lathes with metric 1.5mm pitch leadscrew

Simplified chart

For the mini-lathe banjo and with the original gear set plus 21, 55, 57 and 65 teeth gears.

THREAD A B C D ERROR % REAL TPI
80 TPI 20 65 55 80 0.0606 80.048
72 TPI 40 55 21 65 0.0914 -
64 TPI 45 55 21 65 0.0923 -
56 TPI 35 65 45 80 0.1669 55.907
48 TPI 60 55 21 65 0.0924 -
44 TPI - - - - - -
40 TPI 30 60 55 65 0.0606 40.024
36 TPI 80 55 21 65 0.0928 -
32 TPI 50 65 55 80 0.0606 32.019
28 TPI 35 55 57 60 0.0355 28.010
24 TPI 50 60 55 65 0.0603 24.015
20 TPI 55 40 40 65 0.0606 20.012
18 TPI 50 45 55 65 0.0605 18.011
16 TPI 50 40 55 65 0.0606 16.010
14 TPI 57 30 35 55 0.0355 14.005
12 TPI 50 30 55 65 0.0603 12.007
11 TPI 50 30 60 65 0.0605 11.007
10 TPI - - - - - -
9 TPI - - - - - -
8 TPI 57 35 65 50 0.0225 7.998

Extended chart

These combinations don't fit the mini-lathe banjo, though can be used with other banjo styles..

THREAD A B C D ERROR % REAL TPI
44 TPI 55 50 21 60 0.0399 43.983
44 TPI 55 60 21 50 0.0399 43.983
10 TPI 20 45 80 21 0.0125 10.001
10 TPI 20 21 80 45 0.0125 10.001
10 TPI 80 21 20 45 0.0125 10.001
9 TPI 45 57 50 21 0.0946 9.009
9 TPI 45 21 50 57 0.0946 9.009
9 TPI 50 21 45 57 0.0946 9.009