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You guys appear to be trying to achieve perfection. The original Bygrave
and my copy both achieve the same level of accuracy, one or two minutes
of arc, even though my tube is only 1.5 inches in diameter. I just cut
and tried different percentage settings for my printer until I got a
reasonable fit and it works as well as the original. It's not worth
pulling your hair out to try to get better accuracy.

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Hein Bodahl wrote:




"I have been thinking about using a 50 or 75mm drain pipe and fixed scales.
Around that I would shrink wrap a movable cursor for the cos scale. This
transparent wrap, lined to avoid undue friction, would also cover the
cotan scale.
Around the wrap covering the cotan scale I would wrap a second, movable
cursor for the cotan scale. This second cursor would then move in
conjunction with the cursor for the cos scale, once set, avoiding the
locking problem."

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Then the two cursors would have to be able to rotate and also move up
and down in relationship to the scales and to each other and then
maintain their relationship without slipping.

gl




Richard M. Pisko wrote:
> On Wed, 20 Jan 2010 06:08:28 -0700, Hein Bodahl  wrote:
>
>> How about protecting the scales with a PVC shrink wrap tube ?
>> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200255742807
>
> That sounds better than the stick on clear protective film I used for
> book covers.
>
>> A while back Martin Tali posted PostScript files for the scales, it
>> seems to me that using those would be the easiest way to handle the
>> scaling problem of different diameter tubing.
>
> Yes indeed.
>
>> I have been thinking about using a 50 or 75mm drain pipe and fixed
>> scales.
>> Around that I would shrink wrap a movable cursor for the cos scale. This
>> transparent wrap, lined to avoid undue friction, would also cover the
>> cotan scale.
>> Around the wrap covering the cotan scale I would wrap a second, movable
>> cursor for the cotan scale. This second cursor would then move in
>> conjunction with the cursor for the cos scale, once set, avoiding the
>> locking problem.
>
> Interesting solution.  Sort of like a circular slide rule with the two
> plastic arms and the cursor drawn on each (instead of two disks and
> one cursor); but you could avoid the problem of finding the right
> segment of spiral by using a blunt arrowhead instead of a line.  I
> would miss being able to see both figures at the same time as a last
> check, perhaps.
>
>> This would also provide a cylinder to store the necessary tables.
>
> Yes, and the manual.  :-)
>
>

   

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