Spring back allowance guesstimate

[Morris]

I have a job that requires some 25x25 SHS rolled to a 18" internal radius. Unfortunately I don't have any rollers so will attempt to do it by pulling it around a former.
Any guesses as to how much this will spring back? Pull around a 17" radius? Tighter? Or a different technique?
Thanks.

 

[Agroshield]

I do not know the answer, but factor into your calculations the consequences of it being either under-bent or over-bent. One way may be easier to correct than the other way.

 

[Morris]

Thanks for the reply. I had considered that, it's going to be easier to correct over ending for this particular job.

 

[Maker]

For solid sections you can look up the K-factor for a given material and calculate the radius and angle you need to bend to, for it to spring back where you want. I don't think it would be very accurate for SHS though.

If you've got some spare material, you could do some test bends and calculate the K factor. I've done that at work to design tools for forming rigid coax cable.