PSN-L Email List Message

Subject: Re: Lehman help
From: Paul Jebb pfjebb@..............
Date: Mon, 10 Jan 2000 11:31:41 -0500

Dear Jim,
I just went through this pickle.  If this solution doesn't do it I'll be
surprised.  I was in touch with a Prof. who built one at Kean College. I
followed his suggestion and had no trouble.

The pivot point for the wire coming down off the cross-piece must be ahead of
the pivot point for the knife blade.  So if you can picture the following
triangle ABC where A is the end of the boom, B is the edge of the knife at the
other end of the boom, and C is the upper point where the guy-wire leaves the
upper horizontal cross-piece:  Angle ABC must be less than 90 degrees.  So what
we did was to drill a hole in the upper cross-piece and put an extension through
the cross piece to get the fulcrum out ahead of the knife edge at the bottom.
If this is confusing, please send me an email and I will, send a picture.

It was a major stumbling block for us, please let me know if you get stuck.

Paul Jebb


> Gentlemen,
> I am experiencing rather frustrating problems in getting my Lehman set up.
> I just finished the construction,  and am now trying to get the boom to
> center.  The boom is setup so that it has a VERY slight downward slant from
> level.  I have leveled the base plate and it seems that no matter what I do
> to the leveling screws, the boom either performs a major swing to either the
> right or left. It takes almost NO turning of the leveling screw and the boom
> will go from a center of about 30 degrees to the right, to a center that is
> about the same except to the left.  It seems as though I just can't get the
> darn thing to center up.
> I know a lot of you out there have built the Lehman,  so I'm hoping that
> maybe someone can give me some assistance.
> Please help if you can....
> Jim D. Martin
> New Haven, Indiana
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