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• Gear Tooth Caliper. (Refer Fig. 15.15). It is used to measure the thickness of gear teeth at the pitch line or chordal.thickness of teeth and the distance from the top of a tooth to the chord. The thickness of a tooth at pitch line and the addendum is measured by an adjustable tongue, each of which is adjusted independently by adjusting screw on graduated bars. Read more http://www.mechlook.com/measurement-and-testing-of-gears-measurement-of-individual-elements/
• In the above method, it is seen that both the chordal thickness and chordal addendum are depondent upon the number of teeth. Hence for measuring a large number of gears for set, each having different number of teeth would involve separate Calculations. Thus the procedure becomes laborious and time-consuming one. The constant chord method does away with these difficulties. Constant chord of a gear is measured where the tooth flanks touch the flanks of the basic rack. The teeth of the rack are straight and inclined to their centre lines at the pressure angle as shown in Fig. 15.16. Read more http://www.mechlook.com/measurement-and-testing-of-gears-measurement-of-individual-elements/
• Base Pitch. This is defined as the circular pitch of the teeth measured On the base circle. In Fig. 15.17, AB represents the portion of a gear base circle, CD and EF the sides of two teeth, Read more http://www.mechlook.com/measurement-and-testing-of-gears-measurement-of-individual-elements/

1. 1. MEASURMENTS AND TESTING OF GEARS
2. 2. Terminology of gear toothGear tooth mainly used for transmission of power and motion.
3. 3. Terminology of gear tooth
4. 4. Terminology of gear tooth
5. 5. Terminology of gear tooth1. Addendum2. Dedundum3. Tooth Thickness4. Pitch5. Top land6. Bottom Land7. Face Width8. Circular Pitch9. Pitch Circle10. Base Radius.
6. 6. Terminology of gear toothBase Circle. It is the circle from which involute form isgenerated. Only the base circle on a gear is fixed andunalterable.
7. 7. Terminology of gear toothBase Circle. It is the circle from which involute form isgenerated. Only the base circle on a gear is fixed andunalterable.
8. 8. DO-outside diameter, D- pitch diameter, DB- base diameter, DR- root diameter,
9. 9. Terminology of gear toothPitch Circle Diameter (P.C.D.). It is the diameter of a circlewhich by pure rolling action would produce the same motionas the toothed gear wheel. This is the most importantdiameter in gears.
10. 10. Terminology of gear toothModule. It is defined as the length of the pitch circle diameterper tooth. Thus if P.C.D. of gear be D and number of teeth N,thenmodule (m)=D∕N . It is generally expressed in mm.Diametral Pitch. It is expressed as the number of teeth perinch of the P.C.D.D.P.=D∕N , D expressed in inch.
11. 11. Terminology of gear toothCircular Pitch (C.P.). It is the arc distance measured aroundthe pitch circle from the flank of one tooth to a similar flank inthe next tooth..’. C.P. = ∏D∕N=∏m
12. 12. Terminology of gear toothAddendum. This is the radial distance from the pitch circle tothe tip of the tooth.Its value is equal to one module.
13. 13. Terminology of gear toothClearance. This is the radial distance from the tip of a tooth to thebottom of a mating tooth space when the teeth aresymmetri­cally engaged. Its standard value is 0.157 m.Dedendum.This is the radial distance from the pitch circle to the bottomof the tooth space.Dedendum=Addendum+ Clearance=m+0.157 m=l.157 m.
14. 14. Terminology of gear toothBlank Diameter.This is the diameter of the blank from which gear is a t. It isequal to P.C.D. plus twice the addenda.Blank diameter =P.C.D.+2m.=mN+2m = m(N+2).
15. 15. Terminology of gear toothTooth Thickness. This is the arc distance measured along thepitch circle from its intercept with one flank to its interceptwith t le other flank of the same tooth.Normally tooth thickness.=½ C.P.=∏m∕2
16. 16. Terminology of gear tooth Face of Tooth. It is that part of the tooth surface which isabove the pitch surface.Flank of the Tooth. It is that part of the tooth surface which islying below the pitch surface.
17. 17. Terminology of gear toothline of action. The teeth of a pair of gears in mesh, contact eachother along the common tangent to their base circles,this path is referred to as line of action.
18. 18. Terminology of gear toothPressure angle ø.The angle between the line of action and the commontangent to the pitch circles is known as pressure angle ø.Db=P.C.D × cosøDb=base circle dia
19. 19. Terminology of gear toothPressure angle ø.The angle between the line of action and the commontangent to the pitch circles is known as pressure angle ø.Db=P.C.D × cosøDb=base circle dia
20. 20. Terminology of gear toothBase Pitch. It is the distance measured around the base circlefrom the origin of the involute on the tooth to the origin of asimilar involute on the next tooth.Base Pitch=Base Circumference/ No. of teeth=∏×Db/N=∏×Dp cosø /N=∏mcosø.
21. 21. Terminology of gear toothInvolute Function.It is found from the fundamental principle of the involute, that it is the locus of the end of a thread (imaginary)unwound from the base circle.Involute function δ=tan ø—øWhere ø is the pressure angle.
22. 22. Terminology of gear toothHelix Angle : It is the acute angle between the tangent to thehelix and axis of the cylinder on which teeth are cut.
23. 23. Terminology of gear toothLead Angle : It is the acute angle between the tangent to thehelix and plane perpendicular to the axis of cylinder LEAD ANGLE= 90­helix angle
24. 24. Terminology of gear toothBack Lash : The distance through which a gear can be rotatedto bring its non­working flank in contact with the teeth ofmating gear
25. 25. Anti backlash gear
26. 26. Terminology of gear toothHelix Angle : It is the acute angle between the tangent to thehelix and axis of the cylinder on which teeth are cut.
27. 27. Sources of Errors in Manufacturing Gears The gears (gear teeth) are generally made by one of the following two methods : (i) Reproducing method (ii) Generating method,
28. 28. Sources of Errors in Manufacturing GearsGenerating method, in which the cutting tool (hob formsthe profiles of several teeth simultaneously duringconstant relative motion of the tool and blank.
29. 29. Sources of Errors in Manufacturing GearsReproducing method, in which the cutting tool is form­ed involve cutter, which forms the gear teeth profiles by reproduc­ing the shape of the cutter itself.In this method, each tooth space is cut independently ofthe other tooth spaces,
30. 30. Sources of Errors in Manufacturing GearsThe various sources of errors in thegear made by reproducing method canbe due to(i)incorrect profile on thecutting tool,(ii) incorrect positioning of thetool in relation to the work and(iii) incorrect indexing of theblank.
31. 31. Sources of Errors in Manufacturing GearsThe sources of error when gears aremade by generating method are : (i) Errors in the manufactureof the cutting tool(ii) errors in positioning thetool in relation to the work and (iii) errors in the relativemotion Of the tool and blankduring the generating
32. 32. Measurement of Individual elements Measurement of tooth thickness The permissible error or the tolerance on thickness of tooth is the variation of actual thickness of tooth from its theoretical value. The tooth thickness is generally measured at pitch circle and is therefore, the pitch line thickness of tooth. There are various methods of measuring the gear tooth thickness. (i) Measurement of tooth thickness by gear tooth vernier calliper. (ii) Constant chord method. (iii) Base tangent method. (iv) Measurement by dimension over pins. Gear Tooth Caliper. w=Nm. sin( 90∕N) d= = Nm ∕2[1+2∕N− cos(90∕ N)]
33. 33. Measurement of Individual elementsThe Constant Chord Method.c=constant chord=2A C=∏/ 2 m cos2 ød=addendum—PC=m—∏/ 4 m cos ø sin ø=m(1­ ∏/ 4 cos ø sin ø )
34. 34. Measurement of Individual elementsBase Pitch Measuring Instrument. Thisinstrument has three tips. One is the~!TX53measuring tip, other one is the sensitive tipwhose position can be adjusted by a screw andthe further movement of it is transmittedthrough a leverage system to the dialindicator; and the third tip is thesupplementary adjustable stop which is meantfor the stability of the instrument and its posi­tion cart also be adjusted by a screw. Thedistance between­the fixed and sensitive tip is set to be equivalentto the base pitch of the gear with the help ofslip gauges. The properly set­up instrument isapplied to the gear so that all the three tipscontact the tooth profile. The reading on dialindicator is the error in the base pitch.
35. 35. Measurement of Individual elements The Base Tangent Method. (‘David Brown’ tangent comparator). In this method, the span of a convenient number of teeth is measured with the help of the tangent comparator. This uses a single vernier calliper BD=Nm cos ø [tanø –ø −∏ ∕ 2N +∏ S ∕ N ]
36. 36. Measurement of Individual elements