LATHE OPERATIONS - OD1645 - LESSON 1/TASK 3
each are to be multiplied by a convenient number, will be the number of
teeth in the four gears; the stud gear and the second intermediate gear
representing the smaller term, and the first intermediate gear and the lead
screw gear representing the larger term of the ratio.
For example, to cut 80 threads per inch with a lathe having a lead screw of
8 threads per inch, the ratio would be 8:80 (8 units to 80 units).
Factoring each term, 8=2X4 (factors), and 80=8X10 (factors).
multiplying 2, 4, 8, and 10 each by a convenient number, say 12, the result
is the ratio, 24X48: 96X120. The gearing then must be:
First intermediate gear-----------96
Second intermediate gear----------48
Lead screw gear------------------120
(4) Engaging the Feed. The carriage is connected to the lead screw of the
lathe for threading operations by engaging the half-nut on the carriage
apron with the lead screw. A control is available to reverse the direction
of the lead screw, and it should be determined that the screw turns in the
direction, for left-band or right-hand threading, as desired.
cutter bit from right to left to produce a right-hand thread.
cutter bit from left to right to produce a left-hand thread.
Direction of Feed.
(1) For standard 600 threads of the Sharpe V-type, the American (National)
Standard form and the Unified form, the cutter bit should be moved in at an
angle of 29 so that the left side of the bit does most of the cutting and a
free-curling chip may result.
The direction is controlled by setting the
compound rest at the 29 angle before adjusting the cutter bit perpendicular
to the workpiece axis. The depth of cut is then controlled by the compound
rest feed handle.
(2) For Acme and 29 worm threads, the compound rest is set at one-half of
the included angle (14 1/2) and is fed in with the compound rest.
(3) For square threads, the cutter bit is fed into the workpiece at an
angle perpendicular to the workpiece axis.