My Grizzly G0709 comes with what they call a "Universal Change Gear Box" which lets owners swap between English and Metric threading by the turn of a knob. I admit to not researching it well; looking at the parts lists for the headstock and QCGB I don't see a 127 tooth gear for a "perfect" conversion. Most likely one of the "close enough" combos of gears. Anyway, here's my threading chart and quadrant gears:
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27 is 3 x 3 x 3 while 18 is 2 x 3 x 3 (yes, statements of the obvious); ratio between the two is 3 to 2 (factor out the 9's). I thought about replacing my 66 (2 x 3 x 11) tooth gear with a 44 (2 x 2 x 11) tooth gear in gear box setting "F" to speed things up by 1.5 and take 36 tpi down to 27 tpi? I'm thinking the faster the lead screw turns relative to the spindle, the coarser the thread. Spinning the lead screw faster by 1.5 should result in a coarser thread. I know my math is off because 36 / 1.5 is 24, not 27. . . So I really need a ratio of 1.3333?
Am I thinking this through correctly?
Bruce