L6 measurement of gear tooth

measurement of gear tooth parameters

1. Department of Mechanical Engineering JSS Academy of Technical Education, Bangalore-560060 MECHANICAL MEASUREMENTS AND METROLOGY (Course Code:18ME36B )

2. TEXT BOOKS Mechanical Measurements , Beckwith Marangoni and Lienhard , Pearson Education, 6th Ed., 2006 . Instrumentation, Measurement and Analysis , B C Nakra , K K Chaudhry, 4th Edition, McGraw Hill. Engineering Metrology , R.K. Jain, Khanna Publishers, Delhi, 2009 REFERENCE BOOKS: Engineering Metrology and Measurements , N.V.Raghavendra and L.Krishnamurthy , Oxford University Press.. Further Reference: National Programme on Technology Enhanced Learning ( NPTEL ) http://nptel.ac.in/courses/112104121/1

3. MECHANICAL MEASUREMENTS AND METROLOGY CHAPTER 6: Measurement of Gear Tooth

4. Learning Objectives To understand basic principle of measurement of Gear tooth parameters.

5. Module 2 Gear tooth Measurements Tooth thickness measurement using; Constant chord method Base tangent method Measurement of pitch, Concentricity, Run out and Involute profile . Gear roll tester for composite error.

6. Gear Tooth Measurements Gears are toothed wheels Used to transmit motion / power between two shafts with constant angular velocity ratio + Drives

7. Gear Tooth Measurements Classification of Gears Spur gears Helical gears Herringbone gears Worm and worm gears Bevel gears

8. Base circle Outside circle Pitch circle Root circle Addendum Dedendum Module Circular pitch Tooth thickness Face Flank

9. A basic understanding of the errors in spur gears during manufacturing is required before measurement of different elements of gears. ERRORS IN SPUR GEARS 1. Gear blank runout errors 2. Gear tooth profile errors 3. Gear tooth errors 4. Pitch errors 5. Runout errors 6. Lead errors 7. Assembly errors

10. ERRORS IN SPUR GEARS Gear blank runout errors: have radial runout on its OD surface, due to machining . Gear tooth profile errors: Deviation of the actual tooth profile from the ideal tooth profile. Gear tooth errors: Error in form of tooth thickness. Runout errors: Runout of the pitch circle

11. ERRORS IN SPUR GEARS Pitch errors: Single pitch error or Accumulated pitch error . Single pitch error: Actual measured pitch value Accumulated pitch error: Difference between theoretical summation over any no. of teeth intervals and summation of actual pitch measurement over the same interval of teeth. Lead errors : Deviation of the actual advance of the gear tooth profile from the ideal position.

12. MEASUREMENT OF GEAR ELEMENTS The following elements of gears are important for analytical inspection : 1. Runout 2. Pitch 3. Profile 4. Lead 5. Backlash 6. Tooth thickness

13. MEASUREMENT OF GEAR ELEMENTS Measurement of Runout Runout : Radial runout on the OD surface Runout is measured by a specified probe such as a cylinder, ball, cone, rack, or gear teeth. Measurement is made perpendicular to the surface of revolution .

14. MEASUREMENT OF GEAR ELEMENTS Measurement of Runout A common method of runout inspection, is by a single-probe check, shown in Fig. Uses an indicator with a single probe whose diameter makes contact with the flanks of adjacent teeth in the area of the pitch circle. Single-probe check

15. Measurement of Pitch Two types of instruments are used for checking the pitch. Pitch-measuring Instruments Pitch-checking Instrument

16. Measurement of Pitch Pitch-measuring Instrument Measurement of chordal pitch . Instrument comprises fixed finger and movable finger. The fingers can be set at two identical points on adjacent teeth along the pitch circle. Pitch variation is displayed on dial indicator. Limitation Readings are influenced by profile variations & runout of the gear

17. Measurement of Pitch Pitch-checking Instrument / dividing head fixed (anvil) movable Probe-1 Probe-2

18. Measurement of Pitch Pitch-checking Instrument A pitch-checking instrument is a dividing head , used to measure pitch variations. Has two probes - One fixed (anvil) Other movable (measuring feeler). Connected to dial indicator through levers The instrument is held by two adjacent support on the crests of the teeth. Tooth flank is held between the fixed anvil and the locating support. Measuring feeler (probe 2) senses the next corresponding flank . Instrument is used as a comparator, provides calculation of adjacent pitch error , actual pitch, and accumulated pitch error .

19. PARKINSON’S GEAR TESTER The gear being inspected is meshed with a standard gear , and a dial indicator is used to capture radial errors.

20. PARKINSON’S GEAR TESTER Standard gear is mounted on a fixed frame , the gear being inspected is fixed to a sliding carriage. Dial indicator primarily measure irregularities in the gear under inspection. A dial indicator of high resolution is used to measure the composite error , errors due to runout , tooth-to-tooth spacing , and profile variations .

21. PARKINSON’S GEAR TESTER A Vernier scale enables measurement of the centre distance up to 25 μm . The dial indicator is set to zero Gear under inspection is rotated . Radial variations are indicated by the dial indicator. This variation is plotted on a graph sheet, which indicates the radial variations in the gear for one complete rotation.

22. Tooth thickness measurement by Gear tooth Vernier N = No. of teeth M= Module Pitch circle radius = r p = = To find w (width) w = AC = AB+BC (since AB=BC) w= AC= 2AB From triangle OAB (since OA = r p ) AB = r p x Sin θ w = AC = 2AB = N M Sin ( )   r p θ

23. Tooth thickness measurement by Gear tooth Vernier To find h (height) h = OE - OB Eq.(1) OE = OD+DE OE= r p x m (m = addendum) OE = + m Eq.(2) From triangle OAB (since OA = r p ) OB = r p x Cos θ OB= Cos ( ) Eq.(3) Substitute (2) & (3) in (1) & simplifying h = [ 1+ - Cos ( )]   r p E D Chordal thickness and chordal height θ

24. Base Tangent Method / Measurement over multiple teeth

25. Base Tangent Method In this method, the span of a convenient No. of teeth is measured by David brown tangent comparator. The anvils of the comparator are first set of the base tangent length with the help of slip gauges . Then, slip gauges are replaced by the gear which is to be measured. Reading are taken by the comparator.

26. End of Module