handout 10a1 TOLERANCES - Introduction Nearly impossible to make the part to the exact dimension by any means of manufacturing approach  tolerances of the dimension. - Dimension 30 (mm) won’t be made exactly as 30 (mm) - It may be made as (mm) or (mm). - maximum may be (mm) 30 (a) (b) Fig. 1

handout 10a2 (a)30.01 (shaft) (b) (hole) (a) and (b) are impossible to be assembled without any special treatment (a) (shaft) (b) (hole) (a) and (b) are assembled with a possibility of poor Function of the system (see Figure 2) - situations for assembly of (a) and (b)? Introduction

handout 10a3. Figure 2 Introduction L L’

handout 10a4 Introduction In summary, designers need to specify tolerances for (a) Parts manufacturing interchangeable (b) System function satisfactorily with low cost Specify tighter tolerance only if necessary

handout 10a5 Introduction Objectives of the lecture: 1. To learn the principles behind the standard for determining tolerances. 2. To learn the procedure to determine tolerances based on the standard.

handout 10a6 Basic Concept Definition of Tolerance: Tolerance is the total amount a specific dimension is permitted to vary, which is the difference between the maximum and the minimum limits. Tolerance is always a positive number

handout 10a7 (a) shaft (b) hole Clearance fit (a) shaft (b) hole Interference fit (a) shaft (b) hole Transition fit Basic Concept Three types of fits

handout 10a8 Limits: The maximum and the minimum sizes indicated by a tolerance dimension. The limits for hole are 1.250” and 1.251” The limits for shaft are 1.248” and 1.247” The tolerance can also be defined as upper limit – lower limit on one same dimension upper-limit and lower-limit Lower limit Upper limit Hole tolerance = =0.001 Shaft tolerance = =0.001

Allowances: The difference between the maximum material limits of mating parts. It is the minimum clearance (positive allowance) or maximum interference (Negative allowance) between parts. The limits for hole are 1.250” and 1.251” The limits for shaft are 1.248” and 1.247”

handout 10a10 Allowances: Allowance = Min Hole – Max Shaft 1.Clearance fit 2.Allowance = =0.002 Hole limit Shaft limit Allowance is associated with two dimensions of two parts that form a fit The limits for hole are 1.250” and 1.251” The limits for shaft are 1.248” and 1.247”

handout 10a11 Examples Figure 5 Basic concept Shaft tolerance = =0.001 Hole tolerance= = Allowance= = 0.02 Max clearances= = 0.04

handout 10a12 Tolerance representation The unilateral form The bilateral form The limit form

handout 10a13 In general or Positive First Large Limit on Top Small limit first Tolerance representation