GD&T aims to communicate the design intent in a way that the desired form, fit, function, and interchangeability of feature is conveyed on the drawings without confusion.

GD&T Symbols & Definitions Guide – What You Need to Knowĭo you know all of the GD&T Symbols & Definitions? The ASME Y14.5 is an authoritative guideline and is a design language of geometric dimensioning and tolerancing (GD&T).

GDTP Certification Prep Course (Virtual Classroom).

Tolerance Stack-Up Analysis (Virtual Classroom).

Online Fundamentals of GD&T ASME Y14.5 1994.

Online Fundamentals of GD&T ASME Y14.5 2009.

Virtual Classroom – GDTP Certification Prep.

Virtual Classroom – GD&T for Inspectors.

Virtual Classroom – Tolerance Stack-Up Analysis.

Virtual Classroom – Fundamentals of GD&T.

Therefore, there is no issue with calling out a surface finish and a flatness control on the same surface. Flatness controls the surface at a macro-level, defining the form of the surface. Surface finish controls the surface at a micro-level, defining the required roughness/smoothness of a surface.

Though both surface finish and flatness callouts are limiting the amount of variation in a surface, they are doing it at different levels, so one does not override the other.

The flatness tolerance defines a zone between two parallel planes where the entire surface must lie. It is called out using the GD&T flatness symbol and a tolerance. The surface finish symbol on our drawing helps us determine which manufacturing process to select to achieve the required level of finish.įlatness is called out on a drawing when you want to limit the amount of waviness in a surface without tightening the dimensional tolerance of that surface. For example, sand casting produces a rougher surface finish, and polishing produces a smoother finish. The value included with the symbol tells us the degree of roughness required for the surface.ĭifferent manufacturing processes result in varying surface finishes. When surface finish is specified, it is indicated using the symbols shown below in Figure 1. Surface finish is called out on a drawing to indicate the required level of roughness for a surface. To answer this question, let’s first look at surface finish and flatness individually.

Flatness gd&t symbol