Radii: Need to Know for Preventing Sudden Part Failures
Radii are used to define curved surfaces, rounded edges, or smooth corners. Sharp edges and corners induce stresses and are difficult to manufacture, it is recommended to add rounds and fillets to increase the mechanical strength of the part.
Ignoring radius may lead to high stress concentration zone or in some cases abrupt failure of the part. Keep reading our thoughts on what you need to know for preventing sudden part failures.
Radius
Radius refers to the measurement of the curved surface on a part, both on the inside and outside. They are also used to indicate the rounding of edges at connecting surfaces, called fillets, to increase strength. The radius is denoted by an "R" before the measurement. The radius of an arc is also indicated on drawings, such as "R6" meaning a circle with a 6mm radius.
Maximum and Minimum Radius
Radius that should be maintained below the specified value is given by Maximum Radius and when it is maintained above the specified dimension is given by Minimum Radius. For example, if the maximum allowed value for a radius is 6mm it is given by RMAX6 or R6MAX and if the minimum allowed value for a radius is 6mm it is given by RMIN6 or R6MIN.
Radius with Tolerance
Tolerance on radius is specified in various ways. These can be bilateral or unilateral tolerances. For example, a Radius of 6mm with a tolerance of ±0.1 is annotated as R6±0.1.
Spherical Radius
The letter ´SR´ is used to represent radius of a spherical surface. For Example, SR30, means the spherical surface has a radius of 30mm.
Controlled Radius
A controlled radius is a radius with no flats or reversals allowed on the contour. Controlled radius is shown by ‘CR’ symbol. When a controlled radius is defined a tolerance zone is created by two arcs as per the given tolerance. The part surface must be in this tolerance zone and the radius profile must be without flats or reversals.
