PITCH GEARBOX TUMBLER PITCH ERROR
REQ. SETTING GEAR RESULT %
0.75 48 34 0.7497 -0.046
0.90 40 34 0.8996 -0.046
1.00 36 34 0.9995 -0.046
1.25 28 33 1.2473 -0.214
1.50 24 34 1.4993 -0.046
1.75 20 33 1.7462 -0.214
2.00 18 34 1.9991 -0.046
2.50 14 33 2.4946 -0.214
3.00 12 34 2.9986 -0.046
Cutting metric threads is not the only situation where it will be necessary to set
up the changewheels to cut, what is in imperial terms, a complex value. Another requirement
is when cutting a worm gear. Here though the similarity ends, as whilst there will
be just one required value for a metric pitch this is not the case for a worm gear.
Because of the difference turning worm gears and the changewheel combinations required
are dealt with on separate pages.
When Cutting a Thread
The details in these pages have been given primarily to enable the viewer to better
understand the process of choosing changewheel combinations for complex thread pitches.
I would though suggest that faced with the need to cut such a thread that he of
she looks at my pages that provide the results for all possible combinations of available
gears. These based on gears having 20 to 75 teeth by fives plus 21 teeth and 38 teeth
If you are missing a few of these gears you can still select the combinations that
use only the gears that you have.
There are two sets of lists one for a lathe having an imperial leadscrew and the
other a metric leadscrew.
When cutting a metric thread on a lathe with an 8 TPI leadscrew use the Imperial
list and convert the metric pitch required to an Imperial TPI. Typically, for a 1.5mm
pitch divide 25.4 by 1.5 giving a value of 16.93333 TPI and look up this value. You
will find that as the listing also uses 21 tooth gears, there are more, and more
accurate, values than were listed in Table two.