AnsweredAssumed Answered

Choosing Bend Radii for Design

Question asked by Mike Pogue on Jan 15, 2018
Latest reply on Jan 15, 2018 by Dennis Dohogne

Looking for a more sophisticated understanding of sheet metal design from any gurus.


I have always selected bend radii in the following manor.

  1. Calculate or lookup the min bend radius.
  2. Multiply by 1.5 or 2 if the design allows.
  3. Round off to the next highest fractional size


I have recently, in another thread, been made aware that tonnage goes way up as bend radius goes down. I don't think this has come up before, though, because my parts tend to be thinner aluminum on the order of inches long.

The bigger thing I'm starting to wonder about is air bending. The final radius depends in a weird way on the tooling and thickness and is not likely to be some fractional size. So, if most sheet metal parts are made by air bending, why have fabricators almost always asked me to use fractional sizes? Note that this has changed recently, and I've have some fabricators ask me for goofball radii, like .42, for instance.

My hypothesis is that the fabricators I've used for small aluminum parts for electrical chassis are doing bottom bending and the fabricators I've recently started using for big, steel parts are doing air bending. But, like I said, I'm hoping for guidance from a guru.


So, with all of this context, how to select the inside radius?