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Extension Spring Model in Solidworks 2007

Extension Spring Model in Solidworks 2007

Extension Spring Model in Solidworks 2007

(OP)
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.

RE: Extension Spring Model in Solidworks 2007

"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.

cheers

RE: Extension Spring Model in Solidworks 2007

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

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