On Feb 23, 2:20 pm, Michael Gray wrote:
I have a Cummins 7x12 minilathe and a nicely hand-ground Acme profile tool
I made. Right, so I have to cut a worm at 6.4 tpi. the change gears
with my 16 tpi leadscrew will be:

(30/50) x (40/60)

Can SKS tell me how to set this up so the gears actually mesh? Do I have
to somehow interpose an idler in there somewhere?

Help!
Mike in BC



Mike,
There are two adjustments. When you remove the cover, there is a nut
lower than the change gears.
Called an "adjuster" in this photo, (page 27 "Changing Gears") (PDF
page 29)
http://www.grizzly.com/images/manuals/g8688_m.pdf
That adjuster allows you to correctly set the engagement of the gears
"A" and "B"
There is a nut on the backside of the shaft holding gears "B" and "C",
that nut will allow you to set the clearance of gears "C" and "D".
Proper running clearance is one layer of thin paper. Set "C" and "D"
first.

I don't see that gear combination or pitch. So, like cutting metric
threads on any American leadscrew lathe, DON'T OPEN THE HALF NUT. You
will lose sync, (and have a ~1/27 chance of finding it again.) You
must stop the head, back the tool out, and reverse the rotation to
move back to the start.

Good luck,
Dave