Extension Spring Model in Solidworks 2007

[kathadin]

I have a model created by someone else of an extension spring. It is comprised of a circular "section" (that is the wire dia), swept over the "path" which has five parts: start loop, start transition, helix, end transition, and end loop. The helix is defined by 'height' and 'revolution' parameters. It appears these are calculated. In my equations sheet I have the following formulas:
HelixHeight@Helix=Length-(2*(OD-(WireDia*1.5)))
and
HelixRev@Helix=INT(FreeLength-(2*(OD-(WireDia*1.5)))/WireDia)

I don't quite understand the equations and what "FreeLength" is?

It is shorter than the length - there is a "FreeLength" plane parallel to the right plane at a distance equal to the value entered for this same named variable in the design table.

 

[Theophilus]

I just did some of this for a compression spring. Perhaps this stuff will help?

http://www.engineersedge.com/spring_menu.shtml

http://www.engineersedge.com/Calulators_Online.shtml

I think your free length is the length of the spring "at rest"--no forces being applied.



Jeff Mowry

http://www.industrialdesignhaus.com

Reason trumps all. And awe transcends reason.

 

[CorBlimeyLimey]

"Free Length" is the non-stretched (not pre-loaded) length of the spring. (ie. As purchased) The measurement is usually taken from the inside of the end loops.

 

[CorBlimeyLimey]

http://www.leespring.com/int_learn_extension.asp

 

[drawoh]

kathadin,

Most extension springs are preloaded . Their "free" length is shorter than the coil diameter [×] the number of coils. If effect, if I start to compress a compression spring, it immediately starts to compress. An extension spring has a miniumum extension force below which it does not move.

Your numbers make no sense in a purely mechanical model, but they make a lot of sense if the model is based on an engineering analysis.

This probably is explained in any machine design book you have lying around. If it isn't, you need a new machine design book.

JHG