Detailed introduction on tooth profile of gears. Advantages and disadvantages of each type of profile.

1. Tooth Profiles .
Presented by:-
Prakher singh
2011058 (10)
Kinematics of machine.

2. Gear Terminology .
1. Pitch:-
It is the theoretical circle on which all
calculations are based, the diameter of
pitch circle is called the effective diameter
or pitch diameter.
2. Tooth thickness:-
it is the thickness of the tooth measured
along the pitch surface.
3. Pressure angle:-
Pressure angle in relation to gear teeth, it
is the angle between the tooth face and the
gear wheel tangent.

3. 4. Flank:-
It is the side surface of gear lying below
pitch surface.
5. Dedendum:-
It is the radial depth of tooth from the
pitch circle to the root of the tooth.
6. Adendum:-
It is the radial height of the tooth from
pitch circle to top of the tooth.
7. Adendum circle:-
The circle which limits th top of the gear
tooth is known as addendum circle.
8. Dedendum circle:-
The circle which limits the bottom of the
gear tooth is called dedendum circle.

4. Tooth Profile .
A profile is one side of a tooth in a
crosssection between the outside
circle and the root circle ( dedendum
circle) .
Or
Usually a tooth profile is the curve of
intersection of a tooth surface and a
plane surface normal to the pitch
surface.

5. Conjugate profile .
If the tooth profile of a pair of gears are
so designed that a constant angular
velocity ratio is produced and
maintained during the operation , than
the gears are said to have conjugate
action.
“Hence the tooth of such gears which
perform the conjugate action, are said
to have the conjugate profile”.
The gears in which tooth profile is
conjugate, the tooth of such gears are
thicker at base for maximum moment.

6. ▪ Gears are mostly designed to have the conjugate action to transmit the
desired motion. For making a tooth with the conjugate profile “firstly an
arbitrary profile for one tooth is selected and then a profile of meshing
tooth is found which will give the conjugate action” .
▪ Conjugate profile have some disadvantages as;
1. Difficult to Manufacture.
2. Higher production cost.
3. Standardization is difficult
Some other profiles :-
1. Cycloidal profile.
2. Involute profile.

7. Cycloidal profile .
Cycloid curve.
Cycloid :-
A cycloid is a curve traced by a point on a
circle being rolled on straight line without
slipping.
A cycloid is a curve traced by a point on the
circumference of the circle which rolls
without slipping.
The gear tooth which trace cycloid curve on
its paring gear is said to have a cycloidal
profile.
Types of cycloidal profile :-
1. Epicycloidal profile.
2. Hypocycloidal profile.

8. 1. Elicycloidal profile .
If the circle rolls without slipping
outside the base circle the curve
traced by point on the
circumference is called
“epicycloid” and profile is said as
“epicycloidal profile”.
2. Hypocycloidal profile .
If the circle rolls without slipping
inside the base circle the curve
traced by the point on the
circumference of the base circle is
known as “hypocycloid” and
profile is said as “hypocycloidal
profile” .

9. Cycloidal tooth profile.
The gears in which tooth profile
is cycloidal, the tooth of such
gears are thicker at tip and
thinner at base.
Cycloidal gearing requires two
different curves to obtain
conjugate action.
NOTE :-

10. Involute profile .
The gears whose tooth trace an
involute curve during revolution or
during the process of meshing and
unmeshing with its paring gear the
profile of tooth of such gears is known
as involute profile.
Involute curve :-
An involute curve is obtained from
another given curve ,by attaching an
imaginary taut string to the given
curve and tracing its free end as it is
unwound from that given curve.
Involute curve.

11. Difference between involute and cycloidal
gear .
Cycloidal gear.
1. In cycloidal profile,pressure angle
varies from maximum at the
beginning of engagement,
reduces to zero at the pitch point
and again increases to maximum
at the end of engagement
resulting in improper running of
gears.
2. Due to complex manufacturing,
cycloidal gears are costlier.
Involute gear.
While in involute profile,pressure angle
remains constant throughout the
engagement period.This results in
smooth running of gears.
While involute gears are simple to
manufacture and thus are cheaper.

12. Thank you .