Lesson 10 치수공차와끼워맞춤방식 -...

Chungnam National University 1

치수 공차와 끼워맞춤방식DIMENSIONAL TOLERANCES

AND METHODS OF FITS

Lesson 10

Importance of dimensional tolerances

Definitions

Tolerancing method

Type of fits

Methods of fits

Fits and deviations


IMPORTANCE OF DIMENSIONAL TOLERANCES

The workman cannot be expected to produce the

exact size of part as indicated by the dimensions on

a drawing.

a certain amount of variation on each dimension

must be tolerated.

Especially, the problem of interchangeable

manufacture developed from the making of parts to

a supposedly exact size to the holding of part sizes

between two limits lying so closely together that any

intermediate size would be acceptable.


DEFINITIONS

Basic size (기준치수): reference size

Limit of size

The maximum and minimum sizes permitted for

a specific dimension.

Maximum limit of size (최대허용한계치수)

Minimum limit of size (최소허용한계치수)


최대허용치수 A = 50.025 mm, a = 49.975 mm

최소허용치수 B = 50.000 mm, b = 49.950 mm

DEFINITIONS


Deviation (치수허용차또는허용차) = limit of size -

basic size

Upper deviation =

maximum limit of size - basic size

Lower deviation =

minimum limit of size - basic size

DEFINITIONS


Zero line (기준선)

기준치수 50.000 mm

DEFINITIONS


Tolerances : Total permissible variation in its size

= maximum limit of size - minimum limit of size

= Upper deviation - Lower deviation

Allowance : The intentional difference in correlated

dimensions of mating parts

DEFINITIONS


TOLERANCING METHODS (공차기입방법)

Limit dimensioning : Only the maximum & minimum

dimensions are specified


Plus and minus tolerancing : The dimension of the

specified size is given first, followed by ± expression of

tolerance.

TOLERANCING METHODS


TYPE OF FITS (끼워맞춤의종류)

Clearance (틈새) & Interference (죔새)

Clearance : bore diameter ＞ shaft diameter

Interference : bore diameter ＜ shaft diameter

Clearance fit (헐거운끼워맞춤)

Transition fit (중간끼워맞춤)

Interference fit (억지끼워맞춤)



p. 280 표 13-6


METHODS OF FITS (끼워맞춤방식)

Basic bore system (구멍기준끼워맞춤)

Basic size : use a minimum limit of size of the bore

H5 - H10


상용하는구멍끼워맞춤



Basic shaft system (축기준끼워맞춤)

Basic size : use a maximum limit of size of

the shaft

h4 - h9



상용하는축끼워맞춤



ISO TOLERANCE (IT 기본공차)

0 mm - 3150 mm 의축과구멍에적용

21등급으로나누어적용


IT 기본공차구하는예

6급공차계열의

구멍 ∅ 35 ∅45 : 공차 0.016 30~50에속함

구멍 ∅ 200 : 공차 0.029 180~250에속함

같은 6급공차계열이라도작을수록공차가작다.

정밀도면에서는같음



FIT AND DEVIATION

구멍과축의종류및기호


표시법

구멍 ∅ (치수) (구멍종류기호) (등급)

예 ∅12H7 → 위치수허용차 + 0.018, 아래치수허용차 0

축 ∅ (치수) (구멍종류기호) (등급)

예 ∅100H7 → 위치수허용차 0, 아래치수허용차 -

0.035

끼워맞춤표시

예 H8/g7

FIT AND DEVIATION


예제 ∅30f8 인축의위치수허용차및아래치수허용차를구해보라.

f는위치수허용차가기초가되는치수허용차

표 10-5 → 위치수허용차 -20

표 10-3 → IT 기본공차 : 33

위치수허용차 - 아래치수허용차 = IT 기본공차

(-20) - (아래치수허용차) =33

∴아래치수허용차 = -53

답 :

FIT AND DEVIATION


FIT AND DEVIATION


구멍기준상용끼워맞춤

FIT AND DEVIATION


축기준사용끼워맞춤

FIT AND DEVIATION

Lesson 10 치수공차와끼워맞춤방식 -...

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