Barry and Rex,

Regarding removing the leaf spring:

I generally never bother to bolt down the lower spring support
bracket by installing the nuts on the bolts under the main baseplate.
The pressure of the spring keeps the bracket in place with only
the 1/4" bolts dropped thru the holes.

This makes removing the spring rather easy. The single bolt to the
boom is loosened and the nut removed. Then the spring is (VERY
CAREFULLY) squeezed closed by gripping from both sides. THis frees
it from the boom and lifts the lower bracket from the base. Then 
all the pressure is transferred to one hand to remove the  assembly.

What Barry suggests has the advantage that the point of attachment
under the boom is not disturbed, which is an important consideration
since this effects the mechanical period. Before I remove the bracket
from the boom, I mark its position carefully.


I will give Barry's idea some further thought. Although the brass
support rods are free to rotate during assembly to allow the self-
alignment of the flexures along the direction of maximum tension,
(I actually twang the spring several times to make sure that they align)
they must not rotate during the normal operation of the seismometer.

On another subject, namely the feedback coil/magnet: I have recently
been able to fabricate the magnet assembly with bought parts and wind 
a 4-layer flat-wound coil (not scramble wound: every turn is precisely 
placed) that has a cross-section per side of 0.5 x 0.022" (#36 wire)..
Once I determine the actual constants, I will write up a description
and a list of the parts (from McMaster Carr). The pricy item is the
rare-earth ring magnet at $28. However, it results in a repeatable
outcome without dealing with stereo speakers, and the additional coil
clearance (0.032") solves the problem of the coil jamming when moved
in a short arc. THe ideas can be applied to any hardware/magnet/coil
options. 

Regards,
Sean-Thomas

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