Coil spring rotation during linear deflection

[Pavsta]

Is it true that a coil spring will rotate abouts its vertical axis when it is deflected in the vertical direction?

I have a coil over shock absorber arrangement (like ones seen on rear suspension mountain bikes) and I am wanting to try qauntify the amount of rotation the spring will have during operation. I will then be able to somewhat estimate the amount of friction between the spring and damper to determine whether or not fitting a needle bearing will be necessary.

If anyone knows equations or methods of how this can be done it would be very much appreciated.

Cheers

 

[desertfox]

Hi Pavata

Yes coil springs will rotate while being compressed in the vertical direction it is known as "indexing".
Spring Design by Wahl as reference to rotation during compression and gives formula.
The usual method is to mechanical fix one end of the spring
if it becomes a major problem.

regards
desertfox

 

[desertfox]

Hi Paysta

Sorry the its not "indexing" its called "Ratcheting".
There's lots of things that effect it ie:- Spring Index,Helix angle of coils, amount of compression of spring
etc.
Another way you might get some info is talk to a spring manufacturer.

regards
desertfox

 

[sbozy25]

There is no way to quantify this from a formula. Unfortunately, as of today no one has figured out how to apply a formula to the idea. If you can figure it out... time to start working on your PhD...

what you can do though is easy. Take a random sampeling of say 10 springs and make a mark on one of the coil's OD. Then compress the spring and measure how far around the coil it travelled.

I believe that is how my company would figure the problem out. Although, I asked around and no one has ever asked that question, as most of the time they don't care.