Marchal,
  Try this to get the boom to stay in an equilibrium position (centered):=

  Attach a weight to a sewing thread.  Use enough weight to make the thre=
ad
hang straight.  Hold the thread so that it passes very close (or touching=
)
to the upper attachment point of the wire (which goes to the end of the
boom) and close to the pivot point (at the end of the boom).
   Adjust the tilt--this tilt is in the direction which raises or lowers
the end of the boom.  Adjust this tilt until the hanging string is about
1/4" away from the lower pivot point in the direction of the far end of t=
he
boom.  =

  This should allow the boom to come to equilibrium somewhere near center=
.. =

 The period of swing (observed without any damping) should be somewhere
around 2 to 8 seconds.  This is too short for good Lehman operation--you
should try to get between 16 and 30 seconds.  This is done by reducing th=
e
tilt to give less than the 1/4" above.  The final distance will be roughl=
y
1/16". =

   All this assumes a boom about 24" long.    A shorter boom requires
smaller distances.
  Soft soil should not be a problem if you have a solid base under the
Lehman--for example, a 3 foot square of plywood at least 1/2" thick.
  If your magnet is on the boom, make sure that there is nothing magnetic=

nearby which could be attracted by the magnet.  A distance of 3 feet shou=
ld
be safe. =

  The base plate of my Lehman is 1/2" thick aluminum and I think that thi=
s
is stiff enough.  You can see it on my web site at
   www.webspan.net/~bbarns   It is made from 1/2" steel piipe just the Sc=
i.
Am. article.
  This site also has pictures of Nick Caporossi's Lehman--a neat, lighter=

construction that works well.
 =

Bob Barns

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