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| Imperial threads on a metric lathe... |
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| 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 |
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