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    Re: Bygrave and MHR-1 locking mechanism construction
    From: Gary LaPook
    Date: 2009 Oct 1, 15:43 -0700

    I figured that out, as long as the two pointers maintain their
    relative positions their absolute positions do not matter. I noticed
    when I examined a the Bygrave in London that the pointer to to the
    cotan scale was bent down to be close to the scale to eliminate
    parallax.
    
    
    I am not happy with the one and a half PVC pipe since it is thick and
    heavy and the outside diameter is 1.9" placing the cosine scale .2"
    above the cotan scale.
    My next step is to order a couple of pieces of aluminum tube use for
    antennas. 1.625" O.D. and 1.750" O.D with a thickness of .058". I will
    see how these fit together with my 1.500" drain pipe, 1.520" over the
    existing cotan scale. I am thinking of bushing up the inner tube with
    some wraps of plastic sheeting, if necessary, to minimize the
    difference between the cotan scale and the cosine scale. I want to
    keep the 1.5" drain pipe because the locking mechanism works so well.
    I will be out of the country for the next seven weeks so I  will not
    be able to get to it until mid November.
    
    gl
    
    On Oct 1, 11:49�am, Brad Morris  wrote:
    > There has been some discussion over how the MHR-1 tubes are constructed.
    > Based upon inspection of the MHR-1 in my possession, it appears to be cast aluminium parts.
    > They are probably post machined to obtain the appropriate dimensions and finishes.
    >
    > One thought for Gary. �If the parallax in pointer to surface is an issue, 
    bend the pointer. �Yes, I realize that is pretty dang obvious, but
    > it will eliminate the parallax . �There will be no requirement on how 
    accurately the bend is performed, since the two pointers establish
    > the relative placement of the two scales. �Even if the pointers are twisted, 
    the relative placement of the scales will still be maintained, albeit
    > at a different position than some other Bygrave that does not have that twist in the pointers.
    >
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