ASME GD&T ISO GPS Compliant
A perfect real part (physical workpiece) is impossible to produce or inspect (each manufacturing or measuring process has its own variability or uncertainty).
It is the designer’s responsibility to map functional requirements to geometric variation limits.
Dimensioning and tolerancing stantards define common ruls and definitions to limit geometric variation:
- Size
- Location
- Orientation
- Form
Circularity (ASME) \ Roundness (ISO) is a Form Tolerance limiting the form variation of circular element of a surface.
- Note: Circularity \ Roundness controls only form (not size)
- A callout for circularity shall be specified on a surface and not to a size dimension.
The circumferential line (black solid line), in any cross-section of the surfaces, shall be contained within the Tolerance Zone (Two red dashed concenteric circles)
Circularity\Roundness use cases:
In most cases perfect form at MMC (limits form variation to the size tolerance limits) and other geometric tolerances that affect the circularity of the feature, so Circularity\Roundness is not needed.
When a feature has a circular interaction with a mating part circularity may be nessesary to assure functionality, such as:
- Ball in a Bearing – need to be circular at any cross section to allow smooth rolling
- Dental implants – the gap between the abutment (cone) and the implant (cone) needs to be small enough to prevent bacteria to pass through
- Needle valves – restrict gap between needle and housing to restrict flow
Bottom Line
Geometric specifications (ASME GD&T and ISO GPS) are the tools to prescribe geometric variation limits to assure functionality of a manufactured part.
Standard Geometric Specifications allow us to specify even complex requirements in clear unambiguous manner, no need to “reinvent the wheel”.
In cases of uncertainty, consult an expert (save the time and cost of “reinventing the wheel”, misinterpretation, rework…)
Geometric Tolerances are a tool to map Functional Requirements to Geometric Limits
State Standard & Revision to assure proper Decoding
Write to get it Right
Questions? Ideas? Suggestions?
Write to us – info@TES-tec.net
