GEAR MEASUREMENTSMECHANICAL MEASUREMENTS AND METROLOGY

- AKHIL KUMAR.S

CONTENTS1) INTRODUCTION2) NOMENCLATURE OF GEAR TEETH3) GEAR MEASUREMENT 3.1)Concentricity of gear teeth 3.2)Alignment of each tooth4) ROLLING GEAR TEST5) MEASUREMENTS OF INDIVIDUAL ELEMENTS OF A GEAR6) GEAR TOOTH VERNIER CALIPER

INTRODUCTION TO GEAR MEASUREMENTS

Gear is an mechanical device used for transmission of power and motion Gears can also be used to achieve variable speeds by using different drives They transmit power by meshing with other gear Manufactured precisely and accurately There are mainly two types of profiles are used for manufacturing of the gear teeth. They

are 1) Involute profile 2) Cycloidal profile

1) Involute Profile: Involute gear design was designed Leonhard Euler it is defined as the locus of a point on a straight line which rolls around the cylinder without slipping

2) Cycloidal Profile: It is defined as the curve traced by a point on the circumference of the circle which rolls without slipping on a fixed straight line

TERMINOLOGY OF GEAR TEETH1)PITCH CIRCLE: It is an imaginary circle by which pure rolling action. Would give the same motion as the actual gear2)PITCH CIRCLE DIAMETER: It is the diameter of the circle which by pure rolling action would produce the same motion as the toothed gear.3)PRESSURE ANGLE: It is the angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point4)ADDENDUM: It is the radial distance from the pitch circle to the tip of the tooth 5)DEDENDUM: It is the radial distance from the pitch circle to the bottom of the tooth Dedendum=Addendum + Clearance

6) CLEARANCE: it is defined as the radial distance from tip of a tooth to the bottom of the mating tooth space 7) FACE OF TOOTH: It is that part of the tooth surface which is above the pitch surface 8) FLANK OF THE TOOTH: It is that part of the tooth surface which is lying below the pitch surface 9) CIRCULAR PITCH: it is the distance measured on the circumference of the pitch circle from a point on one tooth to the corresponding point on the adjacent tooth 10) DIAMETRICAL PITCH: It is the ratio of number of teeth on the pitch circle to the diameter of the pitch circle Pd=T/D

11) MODULE:

It is the ratio of pitch circle diameter in millimeters to the number of teeth

m=D/T

12) TOTAL DEPTH: It is the radial distance between the addendum and dedendum circle13) TOOTH THICKNESS: it is the width of the tooth measured along the pitch circle from the intercept with one flank to its intercept with the other flank of the same tooth 14) FACE WIDTH: It is the width of the gear tooth measured parallel to its axis15) WORKING DEPTH: it is the radial distance from addendum circle to the clearance circle16) BACKLASH: It is the difference between the tooth space and the mating tooth thickness

CONCENTRICITY OF TEETH

• Mounting the gear between the bench centers, placing a standard roller in each tooth space and measuring the deviation using a dial indicator

• Using a projector in which case the teeth are brought against a stop and each image of the tooth on the screen should coincide with a line on the screen

• Using a gear testing fixture fitted with a spring loaded slide and dial indicator, in which the spring exerts a constant pressure on the mating teeth and the movements of the dial indicator gives the measure of the eccentricity of the teeth

ALLIGNMENT OF EACH TOOTH

a) Analytical method

1) It is a slow method and tedious

2) It is used to determining the following teeth elements.

profile, spacing, pitch, run out or eccentricity or concentricity, thickness of tooth, backlash

b)The functional method

1) Running test of gear with control or master gear

2) used to determine Composite error, vibration, noise level or variation in action

ROLLING GEAR TEST

Used in mass production of the gear wheels Less time and accurate results Variations of center distance when the gear to be tested is rotated

under spring pressure against a master gear Machine used is called as Parkinson gear tester Reveals any error in tooth form, pitch and concentricity of the pitch

circle Variations in center distance is utilized for determining the errors in

gear wheel by this machine

CONSTRUCTION

PARKINSON GEAR TESTER

Two carriages one fixed and other movable are mounted on the base The movable carriage is spring loaded towards the fixed carriage Two spindles are mounted in a parallel plane on each carriage and are

made to suit the bore of the gear wheels A dial gauge is made to rest against the movable carriage The two gears in mesh are then rotated by hand and variations in the

dial gauge readings are observed

Measurement of individual elements of gear

Tooth thickness is generally measured along the pitch circle and is therefore the pitch line thickness of the tooth

Following are various methods of measuring the gear tooth thickness a) measurement of tooth thickness by gear tooth Vernier caliper b) constant chord method c)base tangent method d)measurement by dimension over pins

GEAR TOOTH VERNIER CALIPER

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