Tolerance analysis is the general term for activities related to the study of accumulated variation in mechanical parts and assemblies. Its methods may be used on other types of systems subject to accumulated variation, such as mechanical and electrical systems. Engineers analyze tolerances for the purpose of evaluating geometric dimensioning and tolerancing

Geometric dimensioning and tolerancing

Geometric dimensioning and tolerancing is a system for defining and communicating engineering tolerances. It uses a symbolic language on engineering drawings and computer-generated three-dimensional solid models for explicitly describing nominal geometry and its allowable variation...

 (GD&T). Methods include 2D tolerance stacks, 3D Monte Carlo simulations, and datum conversions.

Tolerance stackups or tolerance stacks are terms used to describe the problem-solving process in mechanical engineering

Mechanical engineering

Mechanical engineering is a discipline of engineering that applies the principles of physics and materials science for analysis, design, manufacturing, and maintenance of mechanical systems. It is the branch of engineering that involves the production and usage of heat and mechanical power for the...

 of calculating the effects of the accumulated variation that is allowed by specified dimensions and tolerances. Typically these dimensions and tolerances are specified on an engineering drawing. Arithmetic tolerance stackups use the worst-case maximum or minimum values of dimensions and tolerances to calculate the maximum and minimum distance (clearance or interference) between two features or parts. Statistical tolerance stackups evaluate the maximum and minimum values based on the absolute arithmetic calculation combined with some method for establishing likelihood of obtaining the maximum and minimum values, such as Root Sum Square (RSS) or Monte-Carlo methods.

While no official engineering standard covers the process or format of tolerance analysis and stackups, these are essential components of good product design

Product design

-Introduction:Product design is the process of creating a new product to be sold by a business or enterprise to its customers. It is concerned with the efficient and effective generation and development of ideas through a process that leads to new products.Product designers conceptualize and...

. Tolerance stackups should be used as part of the mechanical design process, both as a predictive and a problem-solving tool. The methods used to conduct a tolerance stackup depend somewhat upon the engineering dimensioning and tolerancing standards that are referenced in the engineering documentation, such as American Society of Mechanical Engineers

American Society of Mechanical Engineers

The American Society of Mechanical Engineers is a professional body, specifically an engineering society, focused on mechanical engineering....

(ASME) Y14.5, ASME Y14.41, or the relevant ISO dimensioning and tolerancing standards. Understanding the tolerances, concepts and boundaries created by these standards is vital to performing accurate calculations.

Tolerance stackups serve engineers by:

• helping them study dimensional relationships within an assembly.
• giving designers a means of calculating part tolerances.
• helping engineers compare design proposals.
• helping designers produce complete drawings.

Concerns with tolerance stackups

A safety factor is often included in designs because of concerns about:

• Operational temperature and pressure of the parts or assembly.
• Wear.
• Deflection of components after assembly.
• The possibility or probability that the parts are slightly out of specification (but passed inspection).
• The sensitivity or importance of the stack (what happens if the design conditions are not met).