Worm Drive Dividing Attachment for Mini Lathe

[old_toolmaker]

rebuilder1954,

I made an error stating an 8:1 ratio. What I meant to say is that the worm is 8 threads per inch. That actual ratio in my case is 45:1 (45 turns of the worm = 1 revolution of the spindle). The worm turns the 40 tooth idler gear which does not change the ratio but only the direction. The ratio is determined by the spindle gear vs worm pitch. The circular pitch of or actual tooth spacing for a 1 module gear is .12368". This is very close to .125" so the 8 tpi worm will mesh close enough with the metric module 1 gear. I suppose I could have cut an exact metric pitch but in use I have not noticed any visible error when marking dials One turn of the worm advances the spindle gear by one tooth. I hope this helps clear that up.