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 threading on any lathe you can use the following formula:
TPI = (B/A) x (D/C) x leadscrew pitch.

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