What is Virtual condition in GD&T?

The Concept of Virtual condition is very important in GD&T especially in the case of assembling features. What does it mean ? lets find out.

Virtual condition is a term used to describe the hypothetical perfect form or feature of a part that is used as a reference to establish the tolerance zone. The virtual condition is defined as the maximum or minimum limit of a feature's size, orientation, or location, assuming perfect form and size without any variation.

For example, consider a cylindrical hole that has a specified diameter with a positional tolerance. The virtual condition of the hole would be a perfect cylinder with no deviation from the specified diameter. The positional tolerance would then be applied based on the distance between the actual hole feature and the hypothetical virtual condition.

The virtual condition is an important concept in GD&T because it provides a clear reference point for establishing the tolerance zone, which is the allowable variation between the actual feature and the virtual condition. By defining the virtual condition, engineers can ensure that the part will fit and function correctly within its assembly, while also allowing for manufacturing variation and potential deformation during use.

It is an important concept for ensuring that mechanical parts are designed and manufactured to meet the required functional and dimensional specifications.

In this example, the Virtual condition will be calculated as 92+0.2=92.2 (Largest size) + 0.1 (perpendicularity tolerance ) = 92.3 mm

92.3 is the Virtual condition

If the Feature of size was internal feature of size then the formula would be 92 -0.2 (smallest size) -0.1 = 91.7 mm

Consider this example :

The Virtual condition will be 21-0.2-0.1= 20.7 mm

To learn more about GD&T have a look at this course

Geometric Dimensioning and Tolerancing: Basics

Categories: GD & Tolerancing