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Since you are using a 50 mm tube it should be possible for you to use the two in plug to make a locking mechanism, see http://www.fer3.com/arc/m2.aspx?i=111582

gl


Hein Bodahl wrote:

On 23.01.2010 06:56, Gary LaPook wrote:
  

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.
    

What hair I have left is hardly worth pulling out for any reason :)
I am using my sextant in an armchair 100 miles from the nearest natural
brine.
This is a wonderful, educational hobby for me. As such, nitpicking time
consumption is essential. If someone else also can benefit from it, all
the better.

After some consideration and testing, 50mm (2") seems to do the trick
for me. 50mm  will keep the entire cot scale divided down to at least 1'
on a 35cm (14") long tube. It may not be necessary but I think it looks
good.

I have attached the prototype scales, one continuous cos-cot for A3
sheets to save a little on tube length, and separate cot and cos scales
for A4 sheets in case somebody with an A4 printer wants to try.

As some of the labels will be cut of on the right side I have extended
the scales on the left side. They are intended to be cut vertically
exactly where the scales start at the bottom (digitally if you want to
overlap).

Hein