lower lever has eight positions, each of which places
multiplying the longitudinal feeds by 0.375, as noted
a different gear in the gear train and hence produces
on the index plate.
eight different gear ratios. The three positions of the
On a lathe with a separate feed rod, a feed-thread
upper level produce three different gear ratios for each
shifting lever located at the gear box connects the
of the 8 changes obtained with the lower lever, thus
drive to the feed rod or the lead screw as desired.
When the feed rod is engaged, the lead screw is
double this range by using a sliding compound gear that
disengaged and vice versa.
provides a high- and low-gear ratio in the main gear
train. This gives two ratios for every combination
You can cut metric threads on some lathes that
have an English lead screw (threads per inch
machined on it) by transposing a set of gears in the
The index chart on the gear box also shows the
lead screw to the spindle gear train that provides the
various rates of power longitudinal feed per spindle
correct conversion ratio. You can find information on
revolution that you can get by using the feed
this in handbooks for machinists, in the equipment
technical manual, and through direct correspondence
note that the finest longitudinal feed is 0.0030 inch
with the equipment manufacturer.
per revolution of spindle, the next finest is 0.0032
inch, and so on. To arrange the gear box for power
COMPOUND REST
longitudinal feed, select the feed you wish to use and
follow the same procedure explained for cutting
screw threads, except that you engage the power feed
The compound rest provides a rigid, adjustable
lever instead of the half-nuts. Cross-feeds are not
mounting for the cutting tool. The compound rest
listed on the chart but you can determine them by
6-10