Gallery, Projects and General > How to's

Imperial threads on a metric lathe...

**John Hill**:

One of the many things I have learned here on Madmodders is that the orthadox way of cutting imperial threads on a metric lathe requires the spindle to be stopped at the end of each pass and the carriage motored back to the start position by reversing the lathe.

Having an active mind and all that I was wondering how else this could be done? Supposing for example you cannot easily reverse your lathe! Obviously if the carriage was disengaged and manually wound back to the start the spindle could be allowed to continue to spin and eventually a synchronisation point would come around again and which point the half nuts could be re-engaged and the second cut commenced. The question is how long to wait? So I did the calculations:

This is a list of inch thread pitches from 10 through 60 threads per inch, the equivalent metric pitch and the number of revolutions of a 3mm pitch metric feed screw between one synchronisation point and the next.

10Tpi = 2.540000000mm 50 turns

11Tpi = 2.309090901mm 55 turns

12Tpi = 2.116666667mm 540 turns

13Tpi = 1.953846155mm 195 turns

14Tpi = 1.814285711mm 210 turns

15Tpi = 1.693333333mm 225 turns

16Tpi = 1.587500000mm 80 turns

17Tpi = 1.494117642mm 85 turns

18Tpi = 1.411111111mm 90 turns

19Tpi = 1.336842106mm 95 turns

20Tpi = 1.270000000mm 100 turns

21Tpi = 1.209523801mm 315 turns

22Tpi = 1.154545455mm 110 turns

23Tpi = 1.104347826mm 345 turns

24Tpi = 1.058333333mm 1080 turns

25Tpi = 1.016000000mm 125 turns

26Tpi = 0.976923077mm 390 turns

27Tpi = 0.940740741mm 675 turns

28Tpi = 0.907142857mm 420 turns

29Tpi = 0.875862067mm 145 turns

30Tpi = 0.846666667mm 450 turns

31Tpi = 0.819354837mm 155 turns

32Tpi = 0.793750000mm 160 turns

33Tpi = 0.769696967mm 165 turns

34Tpi = 0.747058822mm 170 turns

35Tpi = 0.725714286mm 1575 turns

36Tpi = 0.705555556mm 180 turns

37Tpi = 0.686486486mm 185 turns

38Tpi = 0.668421059mm 190 turns

39Tpi = 0.651282051mm 585 turns

40Tpi = 0.635000000mm 200 turns

41Tpi = 0.619512191mm 205 turns

42Tpi = 0.604761905mm 630 turns

43Tpi = 0.590697675mm 215 turns

44Tpi = 0.577272727mm 220 turns

45Tpi = 0.564444444mm 225 turns

46Tpi = 0.552173918mm 690 turns

47Tpi = 0.540425534mm 705 turns

48Tpi = 0.529166667mm 2160 turns

49Tpi = 0.518367346mm 2205 turns

50Tpi = 0.508000000mm 250 turns

51Tpi = 0.498039215mm 255 turns

52Tpi = 0.488461538mm 780 turns

53Tpi = 0.479245288mm 265 turns

54Tpi = 0.470370377mm 1350 turns

55Tpi = 0.461818182mm 275 turns

56Tpi = 0.453571429mm 840 turns

57Tpi = 0.445614039mm 285 turns

58Tpi = 0.437931039mm 290 turns

59Tpi = 0.430508471mm 885 turns

60Tpi = 0.423333333mm 900 turns

The first thing to notice is that although there are som rather long intervals there are a suprising number around 100-200. The 49TPI interval is about 20 feet and the much more common(?) 48TPI is almost as long.

The challenge now is to devise some form of counter or other indicator device to indicate when the synchronisation point is coming up. :scratch:

[LATER] Unfortunately it seems my logic was all wrong....

**Tinker**:

how about the other way around for my dad's old South Bend?

**John Hill**:

Tinker, do you know the feed screw pitch?

**John Hill**:

From discussion on another site it appears my logic may be all to heck and that the answer is really 127 turns in every case! :doh:

**sbwhart**:

Hi John

Great bit of calculation as for a counter how about hooking up a claculator as per your idea, I bet you've got that one sorted already, you little Bodger.

:D

Nice one

Have fun

Stew

Navigation

[0] Message Index

[#] Next page

Go to full version