Springback Calculations for Bending Ti Tubing

[Alex Meade]

I've been asked to make bending dies for round titanium tubing for chainstays.  My question is regarding springback calculations. How much overbend or how much smaller does the die radius need to be? Unlike bending flat stock, so far I've not found formulas or even rules of thumb for this.   All sources seem to indicate this needs to be done empirically, but I have a hard time believing nobody has figured out how to calculate springback.

Any hints?

Thanks

Alex

www.alexmeadetools.com

 

[m-gineering]

I've got a copy of a German Text" Das Kalt-Biegen von Rohren,
Wolf-Dieter Franz, Springer Verlag 1961', and they only give some data
for steel tubing and note that there is very little research on tubing,
but that was 1961.

If you find data for Ti, it's probably for CP and not what you are
looking for

> www.alexmeadetools.com <http://www.alexmeadetools.com>
>
> --

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Marten Gerritsen
Kiel Windeweer
Netherlands

[david levy]

Alex,

I have been bending titanium tubing for 35 years and I have not found a ‘calculation’ for spring back because there is such a wide range of yield strength, elongation and amount of annealing depending on the batch of material.  I test bend every batch and generally set my equipment at the target angle, say 15 degrees for a handlebar.  Measure the actual bend and the spring back is the difference between the actual and the measured angle.  I add the difference to my stop and bend the tube again which generally will give me the desired bend angle.  I always check again to confirm I have achieved the desired angle.

Dave Levy
Ti Cycles Fabrication (Bicycle stuff) 
Cedar Ridge Fabrication (Car stuff) 

15707 NW McNamee Road Portland OR 97231 USA
+1 503-621-9670 

Ti Cycles Facebook  |  Cedar Ridge Facebook

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[Mark Bulgier]

It varies with the strength of the material, which is famously complex. Biggest variable is probably the degree of work-hardening. It's my understanding that 3/2.5 gets annealed more than once during the pilgering process because it gets too hard to continue forming. I imagine that aircraft hydraulic tube is held within a narrow hardness range, but the mills are now making tube specifically for bike frames, perhaps with looser tolerances. Plus I've heard many (most?) builders are using annealed tube there (chainstays only), to allow the various kinds of manipulations for tire and chainring clearance. 

I'm not sure about that; my Ti framebuilding was almost 30 years ago and all we could get then was aircraft tube. 

Sorry I can't give you any numbers for amount of springback. TBH we pretty much ignored the actual bend radius, and just bent them as much as necessary for the clearance. Never measured the resulting radius after springback. I can't even imagine a scenario where the radius matters precisely, its just the total amount of bend that matters. Just knowing the resulting radius is going to be some small amount larger than the radius of the bender is close enough for jazz. 

- Mark B in Seattle 

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From: Alex Meade <alexd...@gmail.com>
Sent: Friday, August 29, 2025 9:08 AM
To: Framebuilders
Subject: [Frame] Springback Calculations for Bending Ti Tubing

[Alex Meade]

Marten,

All my engineering texts and handbooks from the 1980s are no better!

Thanks

Alex

[Alex Meade]

Thanks to all who responded.  I think I have enough to go on now.  

Alex