LATHE OPERATIONS - OD1645 - LESSON 1/TASK 3
SIMPLE AND COMPOUND GEAR TRAINS.
(a) Simple Gear Train (figure 45).
1 The basic gears which control the ratio between the spindle speed
and the lead screw speed are the stud gear and the lead screw gear.
stud gear mounts to a shaft which revolves at the same speed as the spindle
and, therefore, can be considered in this discussion as representing spindle
speed in revolutions per minute. The lead screw gear is usually connected
directly to the lead screw and, therefore, moves at the same speed as the
lead screw. In a simple gear train, the stud gear and the lead screw gear
are meshed together or coupled by an idler gear. If the idler gear is used,
it can be of any size or number of teeth convenient for coupling since it
only transmits motion from one gear to the other and does not affect the
ratio of the stud or the lead screw gears.
2 The threads per inch of the lead screw must be known to compute
the gearing for a specific ratio. The rule for determining the number of
teeth of the stud gear and the lead screw gear for a simple gear train is as
follows: Multiply the number of threads per inch of the lead screw and the
number of threads to be cut by a common number. The products will be the
number of teeth that the stud gear and the lead screw gear should have,
respectively. For example, suppose that a