Worm Drive Dividing Attachment for Mini Lathe

[Frank S]

Rob R calculating the ratio of a worm gear drive is done the same way you would calculate any gear train. divide the number of teeth on the worm wheel by the number of teeth on the worm only on a worm the teeth number is the number of tooth or thread starts the most common worms have 1 to 4 starts so to get and 8 to 1 it would mean a worm wheel would have 48 teeth and the worm would have to have 6 starts, if you have an 80 tooth gear and a worm with 1 start you would have an 80 to 1 with 2 starts it would be 40 to 1, with 4 starts 20-1 so to get 8 to 1 without adding an additional gear to a train the worm would have to have 10 starts. Not very practical as the pitch angle of the threads on the worm to match as close as possible the circular or modular pitch of the worm wheel or in your case a spur gear are going to dictate the diameter of the worm plus the angle that the worm must be mounted in relationship to the spur gear
worm gear drives using either spur gears or helical gears and worms instead of a worm wheel have been done for many years but there is a trade off in in contact area and mounting angles