One of my complaints about my Cowells lathe is that with its metric leadscrew I cannot cut the standard BA and imperial threads that I use on most of my models.
The lathe comes as standard with 5 change wheels:64, 56, 32, 20, 16 teeth. The thread cutting set adds additional 50, 40, 35, 30 (2), 32 and a 25 teeth gears
This allows the following threads to be cut:
Driver 1. Driver 2 mm Pitch Inch Pitch T.P.I Driver 1.Driver 2 mm Pitch Inch Pitch T.P.I.
20T 64T 0.312 .0123 81.28 30T 30T 1.000 .0393 25.40
25T 64T 0.390 .0153 65.02 32T 30T 1.066 .0419 23.8
20T 50T 0.4 .0157 63.5 35T 32T 1.093 .0430 23.22
30T 64T 0.468 .0184 54.20 40T 35T 1.143 .0449 22.22
20T 40T 0.5 .0196 50.8 35T 30T 1.166 .0459 21.77
35T 64T. 0.546 .0215 46.44 30T 25T 1.20 .0472 21.16
20T 35T 0.571 .0224 44.45 25T 20T 1.250 .0492 20.32
30T 50T 0.600 .0236 42.33 32T 25T 1.28 .0503 19.84
20T 32T 0.825 .0246 40.64 40T 30T 1.333 .0524 19.05
32T 50T 0.64 .0251 36.69 35T 25T 1.4 .0551 18.14
20T 30T 0.666 .0262 38.10 50T 35T 1.428 .0562 17.78
35T 50T 0.7 .0275 36.28 30T 20T 1.50 .0590 16.93
25T 35T 0.714 .0281 36.56 50T 32T 1.562 .0615 16.25
30T 40T 0.750 .0295 33.87 32T 20T 1.60 .0629 15.87
50T 64T. 0 781 .0307 32.52 35T 20T 1.75 .0688 14.51
20T 25T 0.800 .0314 31.75 64T 35T 1.828 .0719 13.89
25T 30T 0.833 .0328 30.48 64T 32T 2 .0787 12.70
30T 35T 0.875 .0337 29.63 64T 30T 2.133 .0839 11.90
36T 40T 0.875 .0344 29.03 50T 20T 2.500 .0984 10.16
32T 35T 0.914 .0359 27.78 64T 25T 2.56 .1007 9.93
30T 32T 0.937 .0369 27.09 64T 20T 3.2 .1259 7.93
These are the threads I hope to cut:
Thread TPI required metric pitch
OBA 25.41 1
1BA 28.2 0.9
2BA 31.4 0.81
3BA 34.8 0.73
4BA 38.5 0.66
5BA 43.1 0.59
6BA 47.9 0.53
7BA 52.9 0.48
8BA 59.1 0.43
9BA 65.1 0.39
10BA 72.6 0.35
11BA 81.9 0.31
12BA ?? 0.28 (Alan S gives 90.91)
14BA ?? 0.23 ( " 110.4)
16BA 133.7 0.19
Plus: 40TPI, 32TPI and 26TPI.
So any help in calculating the gears I need to cut these would be appreciated
.
Jo
Edit: to add some extra numbers from Alan Stepheny's site after Tel pointed them out
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