[time-nuts] metric / English

Chris Albertson albertson.chris at gmail.com
Fri Dec 16 13:00:58 EST 2011

On Fri, Dec 16, 2011 at 8:48 AM, Brooke Clarke <brooke at pacific.net> wrote:
> Hi Don:
> Sure converting lengths is easy and I have metric, English and weird taps
> and dies, but how do you turn metric threads?

How would you cut 40 tpi or 24 tpi?  You put in the "correct" gears to
drive the lead screw so the tool moves at the desired rate

To cut metric threads they use a gear with the correct ratio to drive
the lead screw.  Yes if the lead screw is 1/8 inch the drive gears
will have some odd ratio but it works.   The reason it works is
because back in 1959 they re-defined the inch to be an EXACTLY 25.4mm.
  From then on gears with integer number of teeth will do the
metric/imperial conversion perfectly.

I think I said a while back that any machine shop that can't figure
this out has likely already gone out of business.

Chris Albertson
Redondo Beach, California

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