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Gear Metrology

Gear metrology

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Gear metrology

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Page 1: Gear metrology

Gear Metrology

Page 2: Gear metrology

Introduction Gears are mainly used for transmission of power or motion

from one shaft to another, without slip. Thus they are positive

in action and provide constant velocity ratio.

Terminology of Gear tooth

Addendum:- This is the radial distance from the pitch circle to

the tip of the tooth. Its value is equal to one module.

Clearance:- This is the radial distance from the tip of a tooth

to the bottom of a mating tooth space when the teeth are

symmetrically engaged. Its standard value is 0.157 m.

Dedendum:- This is the radial distance from the pitch circle to

the bottom of the tooth space.

Dedendum = Addendum + Clearance = m+0.157 m=1.153m.

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Face of Tooth:- It is that part of the tooth surface which is

above the pitch surface.

Flank of Tooth:- It is that part of the tooth surface which is

lying below the pitch surface.

Tooth thickness:- The thickness of tooth, measured along the

pitch circle.

Whole depth= Addendum + Dedendum

Working depth= Addendum + Dedendum - Clearance

Pitch circle:- In every pair of

gears in mesh, the two plain

wheels in contact are assumed

to exist; which are known as

pitch circle.

Pitch point:- It is the point of

contact between the pitch circle

of two gears in mesh.

Page 5: Gear metrology

Circular pitch:- It is the arc distance measured around the

pitch circle from a point on one tooth to a corresponding point

on the adjacent tooth.

Circular pitch = πd/T = πm

d = pitch circle diameter

T = no. of teeth

m = module = d/T

Diametral pitch = Number of teeth

Pitch circle diameter =

T

d

Module = (1/ Diametral pitch)

Back lash = The diameter through which a gear can be

rotated to bring its non-working flank in contact with the teeth

of mating gear.

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Pressure angle or angle of obliquity:- It is the angle which

common normal to the two teeth at the point of contact makes with common tangent to the two pitch circles at the pitch point.

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Tooth thickness measurement:- Since tooth thickness is

defined as length of an arc, it is not possible to measure it

directly. There are various methods of measuring the gear

tooth thickness.

(i) Measurement of tooth thickness by gear tooth vernier

calliper (Chordal thickness method)

(ii) Constant chord method

(iii)Base tangent method

(iv)Measurement by dimension over pins.

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Question :-

Calculate the setting of vernier for a straight spur gear having 40 teeth of

module 3.

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