When a tube is bent it can lose the 100% round shape near and around the bend. This deviation is called ovality, and is defined as the difference between the maximum and minimum dimension of a tubes’ outer diameter.
For example, after bending, a 2” OD tube could measure 1.975”. This difference of 0.025” is the ovality factor, which must fall within the acceptable tolerance. Our standard tolerance is 4% ovality, unless otherwise specified in the parts drawing. See the following example on how ovality is measured and calculated:
Different industries and products may require varying ovality tolerances, ranging from 1.5% – 8%, depending on the end-use of the part.
The primary factors that impact ovality are the “D” of bend and the wall thickness of the material. For tighter bends with thin walled material, it can be challenging to maintain ovality within tolerance, but can be done.
Ovality is controlled by using a mandrel inside the tube or pipe during bending or – in some part specifications – using drawn over material (DOM) from the outset. The lower the ovality tolerance, the more tooling and potential production time.
Verification of the part specifications and tolerance requirements is obtained using specialized inspection equipment. Any necessary adjustments can be transmitted to the CNC machine as needed.
For customers, it is important to specify the tolerances required, as this can have an impact on the tooling used for the project and the production timeframe.
As custom tube bending professionals, we strive to understand and deliver on the tolerances requested by customers. Knowing this information in advance allows us to determine things like type of raw material to order and the best methods to use during manufacturing process. For more information on this topic or about tube bending in general, please contact us.
This blog was authored by Marshall Arndt, Manufacturing Engineer, Sharpe Products. Marshall can be reached at marshalla@sharpeproducts.com.