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On Mon, 18 Jan 2010 12:03:21 -0700, Wolfgang Hasper
 wrote:

> A kit of all three sizes 300 long each would be nice.
> Narrow tolerances are required for the outer diameters
> to fit the scales, the inner diameter is less
> important. If there is a felt lining as on the
> original you can easily compensate for 0.2 mm.
> Aluminium as the material seems preferable but not
> compulsory. I would not like to have stainless steel,
> it is heavy and a pain to machine.

I think a felt liner would be almost essential for prolonged use.
Aluminum tends to blacken surfaces through rubbing.  A coating of the
paper or plastic would help, and I had even thought of spraying the inside
of the outer tube with a thin film of drawing fixative; but I believe that
felt would be the best solution.

As for the parallax worry, a metallic pointer can be bent closer to the
scales if deemed necessary.  The eye can keep the cursor centered in line
with the axis quite well without aid; but a small bit of silver colored
mylar at the base of the cursor will reflect the eye pupil well enough to
allow very repeatable observation positioning.

Just my opinion.

--
Richard . . .


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