From: "Jack Ivey" ivey@..........

Date: Fri, 1 Dec 2006 11:44:08 -0500

I think he was talking about using a clock spring in an odd manner. If you let the spring relax completely, it becomes an open spiral in a plane. If you take the outside end of the=20 spring as one end and the inside end as the other, then pull _axially_ (perpendicular to the plane of the coil, you have a weak spring that starts at zero force at=20 zero axial displacement, and goes up linearly in both the "negative" and "positive" direction. It's not constant force. Also, I'd just like to clarify that for a standard coil spring, having the coils contact when there is no external force applied (like a screen door spring) is a necessary but not sufficient condition to have a zero-length spring. Most such springs are not tightly wound enough to be=20 zero-length, (i.e. they have a positive length at=20 the extrapolated zero force). Jack -----Original Message----- From: psn-l-request@.............. [mailto:psn-l-request@............... On Behalf Of Charles R. Patton Sent: Friday, December 01, 2006 11:27 AM To: psn-l@.............. Subject: Re: Zero-length spring I beg to differ. A standard open coil spring (where there is space=20 between the coil turns) has a finite lenght with zero tension. The=20 tension increases with stretch, but that tenssion starts wth that=20 offset length. On the other hand a spring such as some types of screen=20 door closer springs which are wound such that that even from the start=20 position there is tension. If a plot of the tension vs length is done, it is possible for the tension to go through zero at an imaginary zero=20 length, hence the term "zero length spring.."=20 On the other hand, a clock spring such as you describe may be the=20 reverse -- a constant force spring -- wherein at any length, it is=20 exhibiting constant force. The only versions of these I'm aware of is a type of roll up spring where the spring is slightly crowned to give it a constant straightening force. I believe is is also called a "negator"=20 spring. But I also believe that watch springs are in general just stand wind-up helical coils which really follow a small positive spring curve, i.e., increasing force for increasing wind-up and since it starts out=20 too big and open, it fails the definition of a zero-lenght spring. Regards, Charles Patton ChrisAtUpw@....... wrote: > In a message dated 2006/11/30, tchannel@.............. writes: > >> I think its k that I am unclear of.=20 > > > Hi Ted, > > 'k' is the force constant of the spring in say, pounds per inch > of stretch. This is constant until you get to very large extensions=20 > which change the spiral. > > An example of a zero length spring is an ordinary clock spring=20 > when you pull it along it's shaft axis. > > Regards, > > Chris Chapman __________________________________________________________ Public Seismic Network Mailing List (PSN-L) __________________________________________________________ Public Seismic Network Mailing List (PSN-L)