Hi all,

   I think this is a question about bend allowance but not too sure.  I create 760mm OD ducting from 2.5mm stainless steel.  Having had some problems with flanges fitting I went back to look at the basic maths, having never questioned my predecessor's methods:

The outer circumference of a 760mm tube should be approx 2387mm (760 x π)  I also get this figure when taking a measure of the arc length of the tube in Solidworks.

If I create a 760mm x 2.5mm tube in Solidworks and then flattern it to get my profile, the length routinely comes out at 2379.1mm.  (tube created by making a base-flange from a broken circle sketch.)

Interestingly, when I spoke to our rollers about making up a small piece of tube, they told me the length of the profile would be 2379.5, as they would measure from the centreline of the sheet thickness.

Essentially, given the experience we are having fitting the flanges I actually want my flat length to be closer to the mathematical 2387 rather than Solidworks' default 2379.

What settings do I need to play around with?  Is this issue a case of Solidworks trying to compensate for the stretch and compression of the material during rolling, and if so would you really see 8mm difference in 2.5mm thick sheet?

Many thanks

Oli