Gear Terminology
(A)
Active Profile - Active profile refers to the part of the
gear tooth that in actual comes in touch with the profile of its mating
tooth some where along the line of action.
Addendum - Addendum is radial or the perpendicular
distance that is measured between the tip of the teeth and pitch circle.
Arc of Action - Arc of action is the arc of a pitch circle
via which the tooth moves from the time it first makes any contact with a
mating teeth till the time the contact with mating tooth stops.
Axial Pitch - Axial Pitch is referred to as the distance
measured in an axial plane surface between two corresponding and adjacent
tooth profiles.
(B)
Backlash - Backlash is the point of measure of the quantum
of width of a tooth space by which it exceeds the thickness of the engaging
tooth on pitch circles.
Base Circular Thickness - Base circular thickness is the
length of arc on a base circle between two involute curves resulting in the
profiles of a tooth.
Base Radius - Base radius refers to the radius of the
circle, the involute is generated from here only.
Basic Rack - Basic Rack is there for every pair of a
conjugate involute profile. This basic rack is essentially the profile of
the conjugate gear that has infinite pitch radius.
(C)
Circular Pitch - Circular Pitch means the distance along
the pitch circle or a pitch line, in between corresponding profiles of teeth
that are placed adjacently.
Circular Thickness - Circular thickness is the length of
an arc on a pitch circle that is in between the two sides of the gear tooth.
Contact Ratio - Contact ratio is the ratio formed by the
arc of action to a circular pitch.
Conjugate Action - Conjugate Action is a smooth type of
driving action which produces a constant and uniform angular velocity in a
driven member.
(D)
Dedendum - Dedendum refers to the perpendicular or radial
distance covered between a pitch circle and the tooth space's bottom
portion.
Diametral Pitch - Diametral pitch refers to a ratio that
is formed by the number of teeth to the number of inches in a pitch
diameter. The relation is fixed between a diametral pitch (P) and a circular
pitch (p), denoted by p=p/P.
Double-Helical Gear - Double Helical Gear is the gear of a
cylindrical form that has two sections of teeth, one is at the right hand
and the other is on the left hand, They engage in tandem with the teeth of
an identically designed mating gear.
(E)
Effective or (Active) Face Width - This is in actual the
width of a face which comes in touch with a mating gear.
Equal-Addendum Teeth - This is the teeth of two Gears that
are engaged and having similar addendum.
External Gear - External Gear is the gear that has a teeth
formed on a outer surface of a cylinder or even a cone.
(F)
Face Advance - Face advance refers to the distance on a
pitch circle which a gear tooth travels from the time when at one end the
pitch point contact is made till at the other end another pitch point
contact is made.
Face Contact Ratio - Face contact ratio refers to the
contact ratio made in an axial plane. It also refers to the ratio of the
face width to an axial pitch. In case of bevel and hypoid gears, it refers
to the ratio of face advance to a circular pitch.
Face Width - Face width is the length of a teeth in an
axial plane.
Fillet Curve - Fillet curve refers to a tooth profile's
concave portion, where it is able to join the bottom of a tooth space.
(G)
Gear Blank - Gear Blank is the work piece which is applied
for manufacturing a gear, before there is machining the gear teeth.
Gear Center - Gear center is the center of pitch circle.
Gear Ratio - Gear ratio is the ratio of the number of
tooth in mating gears.
Groove Depth - Groove depth is the depth of clearance
groove between the helices of two
helical gears.
Groove Width - Groove width refers to clearance groove
between the helices of two helical gears.
(H)
Helical Gear - A type of cylindrical gear that has helical
teeth.
Helical Rack - A type of rack that has teeth obliquely
placed to the direction of motion.
Helix Angle - It refers to the angle formed between a
tangent to a helix and the element of a cylinder.
Herringbone Gears - Herringbone is a type double helical
gear, with no clearance groove.
Hub Diameter - Hub diameter refers to the diameter of a
central part of the gear body that encloses the bore and extends the web,
spokes, or the body.
(I)
Inside Cylinder - Inside cylinder is the surface which
coincides with the top of a of teeth of an gear of the nature internal
cylindrical.
Interference - It refers to any type of contact made
between the mating teeth at any other point than that made along the line of
action.
Internal Diameter - It is basically the diameter of a
circle that consists of the top of teeth of
internal gears.
Involute Curve - This is very important term and is
referred to as the curve described by the end of a line which is unwound
from a circle's circumference. Base circle is the circle from where the said
line is unwound.
(L)
Lead - Lead is the axial advance made by the helix for one
complete turn. This is typified in the threads of a cylindrical worm or in
teeth of helical gears.
Lead Angle - The angle formed between a tangent to a pitch
helix and the rotational plane.
Length of Action - It is the distance measured on an
involute line of action via which the point of contact travels during the
action of tooth profiles.
Line of Action - It is the path of contact in case of
involute gears. A straight line that passes via the pitch point and tangent
to the base circles of two mating gears.
(M)
Modified Addendum Teeth - It refers to teeth of two
engaging gears, one or sometimes both of which have addendum that are
nonstandard.
Modified Contact Ratio - It is the contact ratio of
improvised tooth surfaces.
(N)
Normal Helix - It refers a helix on a pitch cylinder which
is normal to a pitch helix.
Normal Plane - The plane that is perpendicular to a
straight line or that forms a tangent to the curved line.
Normal Pressure Angle - It is the pressure angle in a
plane which is normal to the pitch line element.
Normal Tooth Profile - Normal tooth profile is the outline
taking place by the intersection of a tooth surface and a plane which is
perpendicular to a pitch line element.
(O)
Outside Diameter of Gear - It is essentially the diameter
of a circle, comprising the top of the teeth of an external type of gear.
Operating Pitch Diameters - It is the diameter of the
circle on a gear. It is proportional to the gear ratio and the center
distance(actual) at which there will be operation of the gear pair.
Operating Pressure Angle - Operating pressure angle is
ascertained by the center distance at which the gears operate.
Outside Helix Angle - This is the helix angle formed on
the outside cylinder.
(P)
Pinion - Pinion is a gear where number of teeth is small.
In two gears that mesh together one with that has the smaller number of
teeth is known as pinion.
Pitch, Circular - It is the distance measured on the
circumference of a pitch circle between the corresponding points of teeth
that are placed adjacently.
Pitch Circle - It is the circle via which the pitch point
have its center on axis of a gear.
Pitch Cylinder - Pitch cylinder is an imaginary cylinder
drawn in a in a gear which rolls without any slip on a pitch cylinder or a
pitch plane of the other gear.
Pitch Helix - Pitch helix is formed as a result of the
intersection of the thread or surface of a helical tooth with a pitch
cylinder.
(R)
Rack, General - A gear that has its teeth spaced along a
straight line. It is perfect for straight-line motion.
Root Circle - The circle comprising the bottom of tooth
spaces.
Root Cylinder - An imaginary cylinder which is tangent to
the bottom of tooth spaces in a cylindrical type of gear.
Root Radius - Refers to the radius of a root circle.
(S)
Single-Helical Gears - Helical gears that has teeth of on
one hand on each of the gear.
Spur Rack - A rack that has a straight teeth and at 90
degree to the direction of motion.
Surface of Action - An imaginary surface where a contact
takes place between two of the engaging tooth surfaces.
(T)
Tangent Plane - It refers to the plane tangent formed at
the tooth surface at the line of contact.
Tolerance, Tooth Alignment - It is the maximum permissible
amount of variation in tooth alignment. Values are normal to the surface of
tooth.
Tooth Bearing - The part of the tooth surface that
actually comes in touch.
Transverse Circular Thickness - It refers to the thickness
of the circular tooth in the plane of rotation.
(U)
Undercut - A sort of condition that is generated in gear
teeth when a part of the fillet curve is lying inside of a line. It is drawn
as a tangent to a true involute form at its lowest point. Undercut may be
introduced for facilitating the process of finishing.
(W)
Whole Depth (total depth) - It is the radial distance
between an outside circle and a root circle.
Working Depth - It is the extent of greatest depth to
which a tooth of a gear can move into the tooth space of the mating gear.
(Z)
Zone of Action - It the area (rectangular) in a plane of
action. It is restricted by the length of action or the face width.
