[ARC5] Part 6743 - tuning cranks and flexible drive cables.

[J. Forster]

27 TPI is an easy, whole number set of gears (3x9) just as 28 (4x7).  The
feed is geared off the headstock and TPIs tend to be in the ratio of
product of small whole numbers. The most complex gear set I've seen is
254:100 (or 127:50) for cutting Metric.

Just think about it:

#2-56 = 7x8
#4-40 = 5x8
#6-32 = 4x8
#10-24 = 4x6
1/4-20 = 4x5

etc.

-John

===================

[snip]

Signal Corps engineers - the rationale is lost to the ages now.
> Interestingly enough, most lathes still have a 27 TPI setting, at least
> the ones I'm familiar with.
>
> Best of luck,
>    - Mike  KC4TOS