Page 105 - CITS - Fitter - Trade Theory

FITTER - CITS

MODULE 6

LESSON 14: Limit, Fits & Tolerance

Objectives

At the end of this lesson you shall be able to
• define the limit, fit and tolerance and their application
• state the importance of limit, fit and tolerance
• state the hole basics system and shaft basic system.

Limit Fit Tolerance And Their Application

• Define Limit, Fit, And Tolerance:
In engineering and manufacturing, “limit,” “fit,” and “tolerance” are terms used to describe the allowable
variation in dimensions of parts and components. Here are their definitions:
1 Limit: A limit refers to the maximum and minimum dimensions or conditions that a part must meet in order
to be acceptable for its intended use. Limits are often specified as numerical values or ranges within which a
dimension, such as length, diameter, or angle, must fall.
2 Fit: Fit describes the relationship between two mating parts or components in an assembly. It specifies how
snugly or loosely parts fit together when assembled. There are various types of fits, including clearance fits
(where there is intentional clearance between mating parts), interference fits (where parts are intentionally
pressed together with interference), and transition fits (where parts have a combination of clearance and
interference).
3 Tolerance: Tolerance refers to the allowable deviation from a specified dimension or condition. It represents
the acceptable amount of variation permitted in the dimensions or features of a part. Tolerances are typically
specified as numerical values and can be unilateral (allowable deviation in one direction) or bilateral (allowable
deviation in both directions).
• Importance of Limit, Fit, And Tolerance:
Limit, fit, and tolerance are fundamental concepts in engineering and manufacturing with critical importance
for ensuring the quality, functionality, and interchangeability of parts. Here’s why they are significant:
1 Quality Assurance: Limit, fit, and tolerance specifications establish clear criteria for the dimensions and
conditions of parts. By adhering to these specifications, manufacturers can ensure that parts meet the
required standards for quality and performance. This helps in preventing defects and ensuring consistency in
production.
2 Interchangeability: Standardized limit, fit, and tolerance specifications facilitate interchangeability of parts
within assemblies and across different manufacturers. When parts are produced with consistent dimensions
and fits, they can be easily replaced or interchanged without the need for custom adjustments or modifications.
This is particularly crucial in industries where components need to be readily available and compatible, such
as automotive, aerospace, and machinery manufacturing.
3 Functionality and Performance: Properly defined limits, fits, and tolerances are essential for ensuring that
parts function as intended within assemblies. For example, tight fits may be necessary to prevent leakage or
to maintain alignment, while clearance fits might be required to allow for smooth movement or assembly. By
specifying appropriate fits and tolerances, engineers can optimize the performance and reliability of mechanical
systems.
4 Cost Efficiency: Effective management of tolerances can impact manufacturing costs
significantly. Tighter tolerances generally require more precise manufacturing processes, which may involve
higher costs.
However overly loose tolerances can lead to functional issues or increased wear and tear over time, resulting
in higher maintenance or replacement costs. Balancing tolerances based on functional requirements and
cost considerations is crucial for optimizing manufacturing processes and overall product cost

90