3 Replies Latest reply on Mar 28, 2018 12:26 PM by Tom Coulter

    Acute angle k factor

    Tom Coulter

      Hello all,


          I am trying to build bend tables for the sheet metal (typ. .059" Stainless Measured) we bend. Our tables are accurate for angles 90 degrees and more but fail at acute angles. I have pressed 5" test pieces at 135 (so a 45 deg acute bend), 145, 100, and 90. We may have had bottoming trying to press the 145 but the 135 completely airbent. I have been using the bend works PDF http://www.micro-machine-shop.com/Sheet%20Metal%20Bending.pdf to assist me but while it works wonders with 90 deg bends I'm having a real hard time with figuring out acute angles. I set up a sketch jig if you will to help me interpret the dimensions. Has anyone had any luck with this or know any good calcs that work on non 90 degree bends?


      Thank you all so muchsketch jig.JPG

        • Re: Acute angle k factor
          Dennis Dohogne


          Have you done some measuring and bending of coupons to develop K-factors for your materials and your own equipment?  Using some published values is a crapshoot at best.  The rules-of-thumb values in that document will only serve as a sanity check when you develop your own numbers so that you know when you are in the right ballpark with your calculations.


          When we measured our material thicknesses we found them to be significantly different from the published gage values.  That was a huge revelation!  But when we measured, bent and measured some coupons we were able to make amazingly accurate flat patterns in SWX with our resulting K-factors.


          K-factors work very well over a wide range of bending angles, even if the data is measured from coupons bent only at 90 degrees.  However, if the flat pattern is not accurate enough for your acute angle bends then you can just develop another set of K-factors for those acute bends.


          I've attached a drawing and a spreadsheet that a lot of folks have found extremely valuable in calculating K-factors for their own materials and equipment (we even rechecked the material every six months or whenever purchasing changed vendors, whichever came first).  You should first do this for 90 degree bends and see if the K-factors give you good enough results at your acute angles.  If not, then you can modify the techniques for measuring parts bent at acute angles.

            • Re: Acute angle k factor
              Tom Coulter

              Yes, we developed our K factors a few years back after test bending all our materials at 90 degrees and we have used that since then with extremely accurate results since then. We recently started making some parts with acute angles and the flats do not represent what needs to be cut. All the calculators I've seen only input at 90 degrees. Thanks!

            • Re: Acute angle k factor
              Roland Schwarz

              Most reliable bend tables are the result of experimentation and are specific to a set of tools and machines. You're better off running your own experiments.