gauges.pdf

gauges

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 KChaudhry, 4th Edition, McGraw Hill.
•Engineering Metrology, R.K. Jain, Khanna Publishers, Delhi, 2009
REFERENCE BOOKS:
•Engineering Metrology and Measurements, N.V.Raghavendraand 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 2: Limit Gauging

4. •Toequipwithknowledgeoflimitgauges.
Learning Objectives

5. •Explaintheprincipleoflimitgaugesanditsimportanceininspection.
Outcomes

6. Module 2
•Introductiontolimitgauges,Taylor’sprinciple,Typesoflimitgauges,
Numericalonlimitgaugedesign

7. INTRODUCTION
•Inmassproduction,componentsaremanufacturedwiththetolerancelimits,
suggestedbythedesignertofacilitateinterchangeability.
•Variousmeasuringinstrumentsareusedtomeasuretheactualdimensionsand
comparedwiththestandardspecifieddimensionstodecidetheacceptability.

8. INTRODUCTION
•Inmassproduction,gaugesareusedtocheckthecomplianceofthelimitsof
thepartwiththepermissivetolerancelimits,insteadofmeasuringtheactual
dimensions.
•Theterm‘limitgauging’signifiestheuseofgaugesforcheckingthelimitsofthe
components.

9. INTRODUCTION
•Limitgaugesensuresthatthecomponentsliewithinthepermissiblelimits,but
theydonotdeterminetheactualsizeordimensions.
•Gaugesarescalelessinspectiontools,whichareusedtocheckthe
conformanceofthepartsalongwiththeirformsandrelativepositionsofthe
surfacesofthepartstothelimits.

10. INTRODUCTION
•Thegaugesrequiredtocheckthedimensionsofthecomponentswithreference
totwosizesconformingtomaximumandminimumlimitsofthecomponents
(MMC).
•GOgaugesandNOGOorNOTGOgauges,whichcorrespond,totheMMLand
LMLofthecomponent,asdepictedinFig.

11. Gauging

12. Metal limits for hole gauging
Metal limits for shaft gauging

13. INTRODUCTION
•TheGOgaugemanufacturedtothemaximumlimitwillassemblewiththemating
part.
•TheNOTGOgaugecorrespondstothelowerlimitwillnot.
•Hencethenames,GOandNOTGOgauges.
Double-ended plug gaugesSingle-ended GO and NOT GO plug gauges

14. INTRODUCTION
Example:Pistonandcylinderassembly.
•Pluggauge,usedtocheckthecylinderbore,isacopyofthematingpart
(piston)w.r.t.formandsize.
•Gauge,designedasareplicaofthematingpart,tocheckthedimensions,known
as‘standardgauge’.

15. INTRODUCTION
•Theobjectiveindesigningthegaugesistomakecontinuousandaccurate
measurements.
•Clearance fits are preferred for a majority of the assembly operations.
1. MMLs are crucial for effective functioning of the parts.
2. If MMLs slightly exceeds the specified values, assembly becomes impossible.
•If GO gauges fail to assemble during inspection, the components should not be
accepted under any circumstances.

16. Classification of Gauges
(d)Accordingtotheirdesign
(i)Singleanddoublelimitgauges
(ii)Singleanddoubleendedgauges
(iii)Fixedandadjustablegauges
(a)Accordingtotheirtype
(i)Standardgauges
(ii)Limitgauges
(b)Accordingtotheirpurpose
(i)Workshop
(ii)Inspection
(iii)Reference/master/controlgauges
(c)Accordingtotheformofthetestedsurface
(i)Pluggaugesforcheckingholes
(ii)Snapandringgaugesforcheckingshafts
1. Plain gauges

17. Classification of Gauges
2. Adjustable-type gap gauges
3. Miscellaneous gauges
(a) Combined-limit gauges
(b) Taper gauges
(c) Position gauges
(d) Receiver gauges
(e) Contour gauges
(f) Profile gauges

18. Taylor’s Principle
•In1905,WilliamTaylordevelopedaconceptrelatingtogaugingofcomponents.
•Taylor’sprinciple,generallyappliedtotheprincipleoflimitgauging.
•Extensivelyusedinthedesignoflimitgauges.

19. Taylor’s Principle
Taylor’sprinciplestatesthat;
1.“GOgaugeisdesignedtocheckmaximummetalconditions,i.e.,LLHandHLS”.
2.Itshouldcheckasmanyrelateddimensions(form,size,andlocation/position),
aspossible.
3.“NOTGOgaugeisdesignedtocheckminimummetalconditions,i.e.,HLHand
LLS”.
4.Itshouldcheckonlyonedimensionatatime.

20. Taylor’s Principle
5.Duringinspection,theGOsideofthegaugeshouldentertheholewithoutany
forceandNOTGOsideshouldnotenterorpass.
6.ThebasicornominalsizeoftheGOsideofthegaugeconformstoLLHorHLS.
7.ThebasicornominalsizeoftheNOTGOgaugecorrespondstoHLHorLLS.

21. Taylor’s Principle

22. Taylor’s Principle
GO and NOT GO limits of plug gauge

23. Taylor’s Principle
GO and NOT GO limits of snap gauge

24. Important Points for Gauge Design
Pointstobeconsideredwhiledesigninggauges:
1.TheGOgaugesshouldbereplicaofthematingparts.
2.GOgauges,enablesseveralrelateddimensionstobecheckedsimultaneously.
3.Ininspection,GOgaugesmustbeputintoconditionsofmaximumimpassability.
4.NOTGOgaugescheckasingleelementoffeatureatatime.
5.Ininspection,NOTGOgaugesmustbeputintoconditionsofmaximumpassability.

25. Material for Gauges
•Hardandwearresistant,corrosionresistantforaprolongedlife
•Capableofmaintainingdimensionalstabilityandform
•Lowcoefficientofexpansion
•High-carbonsteel,Mildsteel,Chromium-platedetc.

26. Gauge Tolerance (Gauge Maker’s Tolerance)
•Inordertoaccommodatethesedimensionalvariations,ariseduetothe
limitationsofthemanufacturingprocess,sometolerancemustbeallowedinthe
manufactureofgauges,termedasgaugemaker’stoleranceorgaugetolerance
Gauge tolerance = 10% of the work tolerance.

27. Wear Allowance
•TheNOTGOgauge,arerarelyengagedwiththework,thereforedoesnot
undergoanywear.Hence,neednotprovideanallowanceforwearincaseof
NOTGOgauges.
•Wearallowanceof10%ofgaugetoleranceiswidelyacceptedinindustries.

28. Methods of Tolerance Specification on Gauges
ThepresentBritishsystemisinaccordancewithTaylor’sprincipleandiswidely
acceptedinindustries.
Guidelines
1.Thespecifiedtoleranceshouldbewideandconsistentwithsatisfactory
functioning,economicalproduction,andinspection.
2.Duringinspection,theworkthatliesoutsidethespecifiedlimitsshouldnotbe
accepted.

29. Methods of Tolerance Specification on Gauges

30. Methods of Tolerance Specification on Gauges
FromFig.
•TolerancezonefortheGOgaugesisplacedinsidetheworklimits.
•TolerancezoneforNOTGOgaugesisoutsidetheworklimits.
•AmarginisprovidedinbetweenthetolerancezoneforthegaugeandMMLof
theworktoaccommodatewearallowanceforGOgauges.
•WearallowanceshouldnotbepermittedbeyondtheMMLofthework.
•Themagnitudeofwearallowanceis10%ofthegaugetolerance.

31. DesignthegeneraltypeofGOandNOTGOgaugesasperthepresentBritish
systemfora40mmshaftandholepairdesignatedas40H8/d9,giventhat
(a)
(b)40mmliesinthediameterrangeof30–50mm
(c)IT8=25i
(d)IT9=40i
(e)upperdeviationofshaft=–16D
0.44
(f)wearallowanceassumedtobe10%ofgaugetolerance
Numerical

32. Solution
40 H8/d9
Standard diameter steps for 40 mm shaftlies in the range of 30–50 mm
D =
Fundamental tolerance unit = 1.571 μm
For hole quality H8, the fundamental tolerance is 25i= 39.275 μm

33. Fundamental deviation is zero.
Hole limits are;
LLH = 40 mm
HLH = 40.00 + 0.039 = 40.039 mm
Hole tolerance = 40.039 − 40 = 0.039 mm
For hole

34. Fundamental tolerance is 40i.
40i = 62.84 μm = 0.06284 mm ≈ 0.063 mm
For d shaft, FD= −16D
0.44
−79.9576 μm ≈ −0.07996 mm ≈ −0.080 mm
For shaft d9
Shaft limits are as follows;
HLS = (40 –FD) = (40 − 0.080) = 39.92 mm
LLS = 40 − (0.080 + 0.063) = 39.857 mm
Shaft tolerance = 39.92 − 39.857 = 0.063 mm

35. The disposition of tolerances is as shown in Fig

36. Gauge tolerance for Hole
•Gaugetolerance=10%ofworktolerance
•Gaugetoleranceforhole=10%of0.039=0.0039mm
•Wearallowanceforhole=10%ofGaugetolerance.
•Therefore,wearallowanceforhole=10%of0.0039=0.00039mm
Gauge tolerance for shaft
•Gauge tolerance for shaft = 10% of 0.063 = 0.0063 mm
•Wear allowance for shaft = 10% of 0.0063 = 0.00063 mm
Gauge tolerance

37. Design of GO Gauge
The limits of GO Plug gauge are as follows:
•Low limit = Basic size + Wear allowance
•Low limit = 40.00 + 0.00039 = 40.00039 mm
•High limit = Basic size + (Wear allowance + Gauge tolerance)
•High limit = 40.00 + (0.00039 + 0.0039) mm
= 40.00 + (0.00429) = 40.00429 mm
For hole:

38. Design of NOT-GO Gauge
The limits of NOT GO Plug gauge are as follows:
•Low limit = Basic size + Fundamental tolerance for hole
•Low limit = 40.00 + 0.039 = 40.039 mm
•High limit = Basic size + (Fundamental tolerance for hole + Gauge tolerance)
•High limit = 40.00 + (0.039 + 0.0039) mm
= 40.00 + (0.0429) = 40.0429 mm
For hole:

39. For shaft
Design of NOT -GO Gauge (snap)
The limits of GO snap gauge are as follows:
•High limit = Basic size − (Fundamental deviation + Wear allowance)
•High limit = 40.00 − (0.080 + 0.00063) mm
•High limit = 40.00 − (0.08063) = 39.91937 mm
•Low limit = Basic size − (Fundamental deviation + Wear allowance + Gauge tolerance)
•Low limit = 40.00 − (0.080 + 0.00063 + 0.0063) mm
= 40.00 − (0.08693) = 39.91307 mm

40. For shaft
Design of GO Gauge (snap)
Limits of NOT GO snap gauge are as follows:
•High limit = Basic size − (Fundamental deviation + Fundamental tolerance)
•High limit = 40.00 − (0.080 + 0.063) mm
•High limit = 40.00 − (0.143) = 39.857 mm
•Low limit = Basic size − (Fundamental deviation + Fundamental tolerance + Gauge tolerance)
•Low limit = 40.00 − (0.080 + 0.063 + 0.0063) mm
•Low limit = 40.00 − (0.1493) = 39.8507 mm

41. ThedispositionofgaugetolerancesandwearallowancefortheGOandNOT
GOplugandsnapgaugeareschematicallyshown

42. End of Module