1. BY PRATIK SUDRA
GOVERNMENT ENGINEERING COLLEGE,VALSAD

2. Gear drives
 A gear is a toothed wheel with the teeth cut
on the periphery of a cylinder or a cone.
 Gears are mounted on the shafts with key.
 There are two gears mounted, one on each
of the driving and driven shaft.
 Therefore the teeth of one gear is mesh
with the teeth of the other gear.
 The rotation of gear will cause rotation of
the other in the opposite direction.

3. Advantages of gear drives
 Positive drives.
 High transmission efficiency.
 High velocity possible, even up to 60:1
 Velocity ratio will remain constant
throughout.
 Used for low, medium and high power
transmission.

4. Disadvantages of gear
drives
 Require lubrication.
 At very high speeds, produce noise and
vibrations.
 Manufacturing of gears is costly.
 The large number of gear wheels in gear
trains increased the weight of machine.
 Not suitable for shafts having large
centre distance.

5. Terms used in gears
 Pitch circle
 Pitch circle diameter.
 Pressure angle or
angle of obliquity.
 Circular pitch.
 Module.

6. Types of gears
 Spur gears
 Helical gears
 Spiral gears
 Bevel gears
 Worm and worm wheel gears
 Rack and pinion gears

7. Spur gears
 Teeth of the spur gears are
cut on the circumference of
the cylindrical discs.
 Can transmit higher power
because of the contact
between the mating gears is
along lie.
 Use
 transmitting power between
two shafts when the axes of
driving and driven shafts are
parallel & co-planar.
 Machine tools and automobile
gear boxes.

8. Helical
gears
 Teeth are cut in the form of the
helix around the gear.
 Teeth are not parallel to the shaft
axis.
 Two moving gears have identical
helix angle but opposite hand.
 Use
 Transmitting power between two
parallel ,non parallel, non-
intersecting shafts.
 Smooth and quiet running at high
speeds is required.
 Automobile power transmission.

9. Spiral gears
 Same as helical gears
and cut along helical
path.
 Point contact while
curvilinear contact in
case of helical gear
drive.
 Point contact in spiral
gears are more suitable
for transmitting less
power.
 Use:
 Transmit power between
two non-parallel non-
intersecting shafts.

10. Bevel gears
 Cut on conical surfaces.
 Teeth are varying in
cross-section along the
tooth width.
 The axis of two moving
gears are inclined in the
bevel gear.
 Use
 Transmitting power
between two shafts,
when the axis of two
shafs are inclined and
intersect each other.
 Widely use in
automobiles.

11. Worm and
worm wheel
gears
 A worm has one or more
number of helical threads
of trapezoidal shape cut on
it.
 Gear wheel with tooth
profile consists of a small
segment of helix with
engages with the worm.
 Use
 Transmitting power
between two shafts having
the axis at right angle and
non-coplaner.
 Machine tools like lathe,
milling ,drilling machines.

12. Rack and
pinion gears
 Rack is a rectangular bar
consist of a series of straight
teeth cut it.
 Rack is a spur gears infinite
diameter.
 Rack is mesh with another
small gear known as pinion.
 Use
 Convert rotary motion into linear
motion.
 Machine tools like lathe, drilling,
planning machines.
 Measuring instruments.