EME 22342 Gear measurement Notes

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Measurement of Tooth Thickness of Gear

The tooth thickness is to be measured at the pitch circle hence it is not possible to measure it with

conventional vernier caliper or micrometer.

These are various methods of measuring gear tooth thickness.

a. Measurement of gear tooth thickness by using gear tooth vernier caliper (chordal thickness method)

b. Constant chord method

c. Base tangent method

d. Measurement by dimension over pins.

Gear Tooth Varnier Caliper (Chordal Thickness Method)

The tooth thickness is to be measured at the correct points on the tooth on the pitch line shown in

figure.

 It is the arc distance AB which is not possible to measure using simple vernier caliper, it will

not ensure vernier jaws to make perfect contact at A and B at the pitch curve.

       

Therefore modified vernier caliper was developed to measure the gear tooth thickness known as

gear tooth vernier caliper.

In this method, it will measure chordal thickness of gear tooth and chordal addendum.

3.1 Construction and Working of Gear tooth Caliper

It consists of two perpendicular vernier arms with vernier scale provided on each arm.

It is combination of horizontal vernier with vertical vernier and horizontal vernier  has lower jaws to hold the gear tooth during measurement.

The vertical vernier is provided with the slide or blade which moves in vertical direction on vernier scale provided on it.




Procedure for tooth thickness measurement

i. The slide of the vertical vernier is allowed to rest on top of the gear tooth.


ii. Then horizontal vernier jaws are allowed to touch the sides of the gear tooth, at the pitch line AB.

iii.The reading on horizontal vernier scale gives the value of chordal thickness of gear tooth, while reading on vertical vernier scale gives the chordal addendum these measured values are then compared with the specified values.


This method is simple and in expensive. The reading are to be taken for two/three gear teeth  randomly and  average is calculated.


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