COMPUTER AIDED DRAFTING ENGINEERING GRAPHICS II KING ABDULAZIZ UNIVERSITY FACULTY OF MECHANICAL ENGINEERING MENG 204 COMPUTER AIDED DRAFTING ENGINEERING GRAPHICS II Limits and Fits

Fundamental Deviation of Tolerance The fundamental deviation is the deviation which is closest to the basic size and is used to locate the tolerance zone with respect to the basic size.

Fit Fit is the general term used to signify the range of tightness or looseness that may result from the application of a specific combination of allowances and tolerances in mating parts

Bases of Fits The hole basis The shaft basis

Hole Basis In this system, the basic diameter of the hole is constant while the shaft size varies according to the type of fit.

Shaft Basis Here the hole size is varied to produce the required class of tit with a basic size shaft

Engineering fits between two mating parts can be divided into three types: Clearance Interference Transition

Clearance fit In which an internal member fits in an external member (as a shaft in a hole), and always leaves a space or clearance between the parts

Interference fit In which the internal member is larger than the external member such that there is always an actual interference of metal

Transition fit In which the fit might result in either a clearance or interference condition

Selection of Fits – Hole Basis System

Example

Example

Example

Example

Example