PPT: Gear | Design of Machine Elements - Mechanical Engineering PDF Download

 Page 1


INTRODUCTION
• Gears are broadly classified
into four groups, spur, helical,
bevel and worm gears. In
case of spur gears the teeth
are cut parallel to the axis of
the shaft. As the teeth are
parallel to the axis of shaft,
spur gears are used only
when the shafts are parallel.
The profile of the gear tooth
is in shape of involute curve
and it remains identical along
the entire width of the gear
wheel. Spur gears impose
radial loads on the shafts.
Page 2


INTRODUCTION
• Gears are broadly classified
into four groups, spur, helical,
bevel and worm gears. In
case of spur gears the teeth
are cut parallel to the axis of
the shaft. As the teeth are
parallel to the axis of shaft,
spur gears are used only
when the shafts are parallel.
The profile of the gear tooth
is in shape of involute curve
and it remains identical along
the entire width of the gear
wheel. Spur gears impose
radial loads on the shafts.
Gear Terminology
Page 3


INTRODUCTION
• Gears are broadly classified
into four groups, spur, helical,
bevel and worm gears. In
case of spur gears the teeth
are cut parallel to the axis of
the shaft. As the teeth are
parallel to the axis of shaft,
spur gears are used only
when the shafts are parallel.
The profile of the gear tooth
is in shape of involute curve
and it remains identical along
the entire width of the gear
wheel. Spur gears impose
radial loads on the shafts.
Gear Terminology
• Pitch surface : The surface of the imaginary
rolling cylinder (cone, etc.) that the toothed gear
may be considered to replace.
• Pitch circle: A right section of the pitch surface.
• Root (or dedendum) circle: The circle bounding
the spaces between the teeth, in a right section
of the gear.
• Addendum: The radial distance between the
pitch circle and the addendum circle.
• Dedendum: The radial distance between the
pitch circle and the root circle.
• Clearance: The difference between the
dedendum of one gear and the addendum of the
mating gear.
Page 4


INTRODUCTION
• Gears are broadly classified
into four groups, spur, helical,
bevel and worm gears. In
case of spur gears the teeth
are cut parallel to the axis of
the shaft. As the teeth are
parallel to the axis of shaft,
spur gears are used only
when the shafts are parallel.
The profile of the gear tooth
is in shape of involute curve
and it remains identical along
the entire width of the gear
wheel. Spur gears impose
radial loads on the shafts.
Gear Terminology
• Pitch surface : The surface of the imaginary
rolling cylinder (cone, etc.) that the toothed gear
may be considered to replace.
• Pitch circle: A right section of the pitch surface.
• Root (or dedendum) circle: The circle bounding
the spaces between the teeth, in a right section
of the gear.
• Addendum: The radial distance between the
pitch circle and the addendum circle.
• Dedendum: The radial distance between the
pitch circle and the root circle.
• Clearance: The difference between the
dedendum of one gear and the addendum of the
mating gear.
• Face of a tooth: That part of the tooth surface
lying outside the pitch surface.
• Flank of a tooth: The part of the tooth surface
lying inside the pitch surface.
• Circular thickness (tooth thickness) : The
thickness of the tooth measured on the pitch
circle. It is the length of an arc.
• Tooth space: The distance between adjacent
teeth measured on the pitch circle.
• Backlash: The difference between the circle
thickness of one gear and the tooth space of the
mating gear.
Page 5


INTRODUCTION
• Gears are broadly classified
into four groups, spur, helical,
bevel and worm gears. In
case of spur gears the teeth
are cut parallel to the axis of
the shaft. As the teeth are
parallel to the axis of shaft,
spur gears are used only
when the shafts are parallel.
The profile of the gear tooth
is in shape of involute curve
and it remains identical along
the entire width of the gear
wheel. Spur gears impose
radial loads on the shafts.
Gear Terminology
• Pitch surface : The surface of the imaginary
rolling cylinder (cone, etc.) that the toothed gear
may be considered to replace.
• Pitch circle: A right section of the pitch surface.
• Root (or dedendum) circle: The circle bounding
the spaces between the teeth, in a right section
of the gear.
• Addendum: The radial distance between the
pitch circle and the addendum circle.
• Dedendum: The radial distance between the
pitch circle and the root circle.
• Clearance: The difference between the
dedendum of one gear and the addendum of the
mating gear.
• Face of a tooth: That part of the tooth surface
lying outside the pitch surface.
• Flank of a tooth: The part of the tooth surface
lying inside the pitch surface.
• Circular thickness (tooth thickness) : The
thickness of the tooth measured on the pitch
circle. It is the length of an arc.
• Tooth space: The distance between adjacent
teeth measured on the pitch circle.
• Backlash: The difference between the circle
thickness of one gear and the tooth space of the
mating gear.
• Module (m): Pitch diameter divided by number
of teeth. The pitch diameter is usually specified in
inches or millimeters; in the former case the
module is the inverse of diametral pitch.
• Fillet : The small radius that connects the profile
of a tooth to the root circle.
• Pinion: The smaller of any pair of mating gears.
The larger of the pair is called simply the gear.
• Velocity ratio: The ratio of the number of
revolutions of the driving (or input) gear to the
number of revolutions of the driven (or output)
gear, in a unit of time.