Searching for information regarding LaCoste "zero length" springs a year =
or two ago; I came across the following documents, which may be of some =
use during this current discussion. =20

You will need to retrieve two patents. These patents are accessible as =
PDFs through a free patent search web site like Free Patents Online; =
however, you need to create an account, for free. Go to:
http://www.freepatentsonline.com/index.html =20

LaCoste (1942) Patent 2293437:
This patent illustrates a variety of different types of zero lengths =
springs, including both helical tension and spiral springs. A lot of =
food for thought for amteur instrument builders!

Willmore (1966) Patent 3292145:
This patent covers the design of a tapered leaf spring. Patent was cited =
in the BSSA 1982 article describing the STS-1 Seismometer.
I made a curved tapered leaf spring, cut out of a flat tempered steel =
plastering knife using an abrasive cutting disc mounted in a Dremel =
tool. Hand formed (curved) the metal leaf spring by partially wrapping =
it around a metal bar clamped in a rigid bench vice. Spring later used =
to develop a 4-5 second natural period vertical seismometer, with =
feedback for closed loop period extension.

If you are interested in how LaCoste and Romberg make their zero length =
tension springs, download the following 3 meg PDF from:
http://www.gravitymeter-repair.com/images/gdmanual.pdf
It's the LaCoste and Romberg Instruction Manual for the model G & D =
Gravity Meters. Starting at page 4-44, under PHYSICS OF THE SENSOR, =
there are 4 pages of information.

Regards,

Allan

-----Original Message-----
From: psn-l-request@..............
[mailto:psn-l-request@................. Behalf Of John or Jan Lahr
Sent: Friday, December 01, 2006 9:26 AM
To: psn-l@..............
Subject: Re: Zero-length spring


Hi Charles,

I think that a spring with this configuration is what Chris was=20
describing, and it would be a "zero-length" spring.

I sent this just before Jack's message came in.  It bounced back due=20
to being too large with the image, so I've placed the sketch here:
http://www.jclahr.com/science/psn/as1/heli/spring.GIF

This isn't the same as the spring effect of a tape measure, where the=20
metal tape is slightly crowned.

I've modified my page on zero-length springs to emphasize Jack's=20
point that not every spring that has coils touching when relaxed will=20
have "zero-length."

Cheers,
John


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