Bent Radii Practices
Bend radii practices in CAD models and print tolerancing for thin gage sheet metal parts when using Air Bending techniques
For the majority of thin gage sheet metal designs (.024” to .134” thick CRS, SS or Alum), we recommend using the material thickness for the inside bend radius. Doing this will generally approximate the actual outcome and will typically make your bend reliefs the proper depth to meet good forming practices.
When dimensioning and tolerancing the bend radii on your prints, we recommend using a scheme like this: bend radii = material thickness + .062" as a max size (specifying a lower limit is usually not required). This will allow your sheet metal vendor to select from their standard form tooling for their various forming machines, but will stop them from using a huge radius that could affect the fit and function of the part. In some cases using bend radii = material thickness + .031” as a max could be ok, but it might be on the tight side which could limit your sheet metal vendor from using their typical/standard form tooling.
Please note: When using material less than .031" thick, we suggest not using less than .031 for the bend radii. Also, when using material that inherently does not bend well (like 6061-T6 aluminum), or where a part will be subjected to severe vibration or stress, you should default to appropriate engineering and industry standards for the proper bend radii allowed.
Finally, when a specific radius is needed for aesthetic reasons or to mate with or match other components, it is best to consult with a reputable sheet metal manufacturing company regarding the different radii they have tooling for (or can get) and for what the tolerance will need to be on it.
Caveats aside, the take away here is to consider using the material thickness for your bend radii, it is a great drafting practices to follow.