RideTheGearTrain free online software was used to set up the gear train for single-point turning a metric 8mm-1.25mm pitch thread on an imperial lathe with an 8 TPI lead screw. How to avoid disengaging the half-nuts on the lead screw, and avoiding use of the thread dial indicator. This makes use of the ability to run the motor in reverse.
Three previous videos in this playlist explain how to modify a single phase capacitor motor to run in reverse and how to install a DC motors with speed control. The DC motor makes screw cutting much easier, as demonstrated in this video.
COMMENT:
@Kev7325 pointed out something that he found confusing. It is not really an error, but it may be confusing. RideTheGearTrain.com showed the correct solution and provided a diagram of how the gear train should be set up. But this is followed by a short video clip of my actual gear train at 2:30 minutes, and it had not been set up that way. It was still set up for cutting imperial threads on this imperial lathe.
However if you continue watching to 3:30 minutes there is an explanation and it shows how the gear train has to be altered. In the 2:30 minute video clip the 127 tooth gear was acting as an idler gear which does not affect the overall gear ratio. To make the imperial lathe cut a metric thread it is necessary to remove the 56 tooth leadscrew gear, put a spacer behind it, and make it mesh with the 100 tooth gear instead of the 127T gear. That gives the correct setup for cutting metric threads. This process of changeing the gear train is clearly shown at 3:30 minutes.
Checking the calculation of the gear train gear ratio:
GTR = 20/127 x 100/56. This introduces the ratio 100/127. Note that 127/100 =1.27 and if this is multiplied by 2 gives 2.54 and there are 2.54 cm in one inch. So this is like dividing by 2.54.
