Gear drives transmit rotational motion between two shafts. Gears are mounted on parallel shafts and their teeth mesh to transfer rotation in opposite directions. Gear drives provide positive, efficient transmission of high torque and velocity over a constant ratio. While requiring lubrication and producing noise at high speeds, gear drives are used for low to high power transmission in machines like automobiles and manufacturing equipment. Common gear types include spur gears, helical gears, bevel gears, worm gears, and rack and pinion gears, which transmit motion between parallel, inclined, perpendicular, or rotary and linear shafts.

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.