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.
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:
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