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Chapter End INTRODUCTION TO TOLERANCES AND FITS Chapter End INTRODUCTION TO TOLERANCES AND FITS 1.1 TERMINOLOGIES IN TOLERANCES AND FITS 1.1.1 Size / Dimension 1.1.2 Limiting deviation 1.1.3 Tolerance 1.1.4 Fit 1.1.5 Diagram of disposition of tolerance zones for fit End Home 1.1.1 Size / Dimension a) Nominal size b) Actual size c) Limits of size End Home 1.1.1 Size / Dimension a) Nominal size Nominal size is the designation used for the purpose of general identification It is obtained by calculation for strength and chosen in series of Standard preferred sizes Designation : D, d D (For hole or enveloping surface) d (For shaft or enveloped surface) End Home Nominal size Ra5 Ra10 Ra20 1 1,1 1,2 1,2 1,4 1,6 1,6 1,6 1,8 2,0 2,0 2,2 2,5 2,5 2,5 2,8 3,2 3,2 3,6 4,0 4,0 4,0 4,5 5,0 5,0 5,6 6,3 6,3 6,3 7,1 8,0 End 8,0 9,0 Home Ra40 Ra5 Ra10 Ra20 1,05 1,1 1,15 1,2 1,3 1,4 1,5 10 10 10 1,6 1,7 1,8 1,9 2,0 2,1 2,2 2,4 16 2,5 2,6 2,8 3,0 3,2 3,4 3,6 3,8 25 4,0 4,2 4,5 4,8 5,0 5,3 5,6 6,0 40 6,3 6,7 7,1 7,5 8,0 8,5 9,0 9,5 63 11 12 12 14 16 16 18 20 20 22 25 25 28 32 32 36 40 40 45 50 50 56 63 63 71 80 80 90 Ra40 Ra5 Ra10 Ra20 Ra40 Ra5 Ra10 Ra20 Ra40 10 10,5 11 11,5 12 13 14 15 100 100 100 100 105 110 120 125 130 140 150 1000 1000 1000 1000 1060 1120 1180 1250 1320 1400 1500 16 17 18 19 20 21 22 24 160 160 170 180 190 200 210 220 240 1600 25 26 28 30 32 34 36 38 250 250 260 280 300 320 340 360 380 2500 40 42 45 48 50 53 56 60 400 400 420 450 480 500 530 560 600 4000 63 67 71 75 80 85 90 95 630 630 670 710 750 800 850 900 950 6300 110 125 125 140 160 160 180 200 200 220 250 250 280 320 320 360 400 400 450 500 500 560 630 630 710 800 800 900 1120 1250 1250 1400 1600 1600 1800 2000 2000 2240 2500 2500 2800 3150 3150 3550 4000 4000 4500 5000 5000 5600 6300 6300 7100 8000 8000 9000 1600 1700 1800 1900 2000 2120 2240 2360 2500 2650 2800 3000 3150 3350 3550 3750 4000 4250 4500 4750 5000 5300 5600 6000 6300 6700 7100 7500 8000 8500 9000 9500 a) Nominal size R R R R R R R R R R Ra5 Ra10 Ra20 Ra40 Ra5 Ra10 Ra20 Ra40 Ra5 Ra10 Ra20 Ra40 10 10 10 10 100 100 100 100 1000 1000 1000 1000 10,5 11 105 11 110 11,5 12 12 12 125 125 16 16 14 16 140 160 160 160 20 18 20 180 22 24 End Home 1250 200 200 140 1400 1600 1600 1600 220 240 1600 1700 1800 1800 1900 2000 2000 210 220 1400 1500 180 200 1250 1320 190 21 22 1250 170 19 20 125 160 1120 1180 150 17 18 1120 130 15 16 110 120 13 14 1060 2000 2120 2240 2240 2360 1.1.1 Size / Dimension b) Actual size Actual size is the dimension as measured on a manufactured part Designation: Dt , dt End Home 1.1.1 Size / Dimension c) Limits of size + Maximum limit of size Designation : Dmax , dmax + Minimum limit of size End Home -0,040 -0,073 Ø30 Ø18 +0,018 Designation : Dmin , dmin 1.1.2 Limiting deviation a) Upper limiting deviation Designation : ES, es Hole upper deviation : ES = Dmax D Shaft upper deviation : es = dmax d b) Lower limiting deviation Designation : EI , ei End -0,040 -0,073 ei = dmin d Ø30 Shaft lower deviation: +0,018 EI = Dmin D Ø18 Hole lower deviation: Home 10 1.1.3 Tolerance Tolerance is the difference between the maximum limit of size and the minimum limit of size It is an absolute value without sign • + Hole tolerance : TD = Dmax Dmin = (ES + D) (EI + D) = ES EI • End + Shaft tolerance : Home Td = dmax dmin = es ei 11 1.1.3 Tolerance * Designating sizes on drawings includes : Nominal size Limiting deviations (upper and lower deviations) Bilateral tolerance End Home Ø1400,0125 -0,008 Ø40 -0,033 Unilateral tolerance 12 1.1.4 Fit When two mating parts are to be assembled, the relation resulting from the difference between their sizes before assembly is called a fit Enveloping part Enveloping surface d=D Enveloped surface d=D Enveloping surface Enveloping part Enveloped part Enveloped surface End Home Enveloped part 13 1.1.4 Fit - Concept of fit only exists in mass production - Basic sizes of mating parts are the same : D = d types of fit can be distinguished: End • a) Clearance fit • b) Interference fit • c) Transition fit Home 14 a) Clearance fit Designation: S (Clearance) Smin Smax Applied : For movable joints (running, sliding or both) between the mating components TD End Home dmax dmin d=D Dmin Dmax Td 15 a) Clearance fit + Maximum clearance: Smax = Dmax – dmin = (ES + D) – (ei + d) = ES – ei + Minimum clearance: Smin = Dmin – dmax = EI – es Smax + Smin + Average clearance: Stb = + Tolerance of fit: Ts = Smax – Smin = TD + Td End Home 16 b) Interference fit Designation : N (Interference) Nmin dmax d=D Dmin Dmax Home dmin Td TD End Nmax Applied : For fixed joints excluding relative motion between the mating components 17 b) Interference fit + Maximum interference: Nmax = dmax – Dmin = es – EI + Minimum interference: Nmin = dmin – Dmax = ei – ES + Average interference: + Tolerance of fit: End Home Ntb = Nmax + Nmin TN = Nmax – Nmin = TD + Td 18 c) Transition fit Nmax End Home dmax dmin Td d=D Dmin Dmax TD Smax It is a fit where both clearance and interference may occur in the coupling 19 c) Transition fit Applied : For fixed joints only in conjunction with an additional fastener, such as a key, pin, screw … + Maximum clearance: Smax = Dmax – dmin = ES – ei + Maximum interference: Nmax = dmax – Dmin = es – EI + Tolerance of fit End Home TS,N = Smax + Nmax = TD + Td 20 1.1.5 Diagram of disposition of tolerance zones for fit d = 50 D = 50 +0,025 0,009 0,025 mm TD ES =+25 EI = Line D = d = Ø Ø 50mm es = -9 End Home ei = -25 Td 21 1.1.5 Diagram of disposition of tolerance zones for fit D = 50 +0,025 μm μm TD Td Clearance fit Home μm TD Zero line End 0,009 d = 50 0,025 TD Zero line Td Interference fit Zero line Td Transition fit 22 1.2 THE CONCEPT OF INTERCHANGEABILITY Interchangeability is an ability that an part (a component) can be replaced at random by another of the same type without any need for adjustment or repairing Two modes of assembly : a) Full Interchangeability The production of mating parts can be carried at different places Benefits Reducing manufacturing and assembly time considerably The replacement of worn-out or defective parts becomes very easy Applied for standardized or spare parts b) Partial Interchangeability End Home 23 b) Partial Interchangeability / Group Interchangeability mm III T’D II III’ I D = d = Ø 30mm TD Smin Line II’ T’d Smax I’ Td Group I : 30 DI 30,01 D = 30 +0,010 D = 30 +0,030 Group II : 30,01 < DII 30,02 Group III : 30,02 < DIII 30,03 Group I’ : 29,984 dI’ 29,994 0,006 d = 30 0,016 d = 300,016 +0,014 End Home Group II’ : 29,994 < dII’ 30,004 Group III’ : 30,004 < dIII’ 30,014 24 b) Partial Interchangeability / Group Interchangeability • The tolerances of mating parts are allowed to increase in order to meet machining requirements • Machined parts are measured and sorted into groups by dimension prior to assembly process • Defect rate probability could be higher than usual Applied for assembly process in a factory’s production line End Home 25 ... 71 80 80 90 Ra40 Ra5 Ra10 Ra20 Ra40 Ra5 Ra10 Ra20 Ra40 10 10 ,5 11 11 ,5 12 13 14 15 10 0 10 0 10 0 10 0 10 5 11 0 12 0 12 5 13 0 14 0 15 0 10 00 10 00 10 00 10 00 10 60 11 20 11 80 12 50 13 20 14 00 15 00 16 17 18 19 ... 11 ,5 12 12 12 12 5 12 5 16 16 14 16 14 0 16 0 16 0 16 0 20 18 20 18 0 22 24 End Home 12 50 200 200 14 0 14 00 16 00 16 00 16 00 220 240 16 00 17 00 18 00 18 00 19 00 2000 2000 210 220 14 00 15 00 18 0 200 12 50 13 20 19 0... 210 220 14 00 15 00 18 0 200 12 50 13 20 19 0 21 22 12 50 17 0 19 20 12 5 16 0 11 20 11 80 15 0 17 18 11 20 13 0 15 16 11 0 12 0 13 14 10 60 2000 212 0 2240 2240 2360 1. 1 .1 Size / Dimension b) Actual size Actual