# CAM

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```					              Gears

Inter American University of Puerto Rico
Mechanism Design
MECN 4110

Chapter 9
Mechanical Transmissions
Chains    Belts        Gears
Types of Gears
Spur Gears   Pinion

Gear
Spur Gears - Types

External Set: Opposite   Internal Set: Movement
Movement            in the same direction
Pinion and Gear
The Fundamental Law of
Gearing
   The angular velocity
ratio between the gears
of a gearset remains             out    rin d in
constant throughout the     mV        
mesh.                            in    rout d out
   The angular velocity
ratio (mV) is equal to           in    rout d out
the ratio of the radius     mT        
of the input gear to that        out    rin d in
of the output gear
   The torque ratio (mT)
The Involute Tooth Form
   The cycloid     and the
involute:           curve
characteristics
   The involute is a curve
which can be generated
by unwrapping a taut
string from a cylinder
(called the evolute).
Features of this involute
curve:
The Involute Tooth Form
   The string is always tangent to the cylinder.
   The center of the curvature of the involute is
always at the point of tangency of the string
with the cylinder.
   A tangent to the involute is then always
normal to the string, the length os which is
the instantaneous radius of curvature of the
involute curve.
14.5o, 20o and 25o
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Gear Tooth Nomenclature
Contact Ratio

If mp is 1, then one tooth is leaving contact just as the next is beginning
contact. Spur gears [1-2]. The minimum contact ratio for a smooth operation
is 1.2. A minimum contact ratio of 1.4 is preferred and larger is better. Most
spur gearsets will have contact ratios between 1.4 to 2.

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