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> But then there's another stage in the motion, where backlash can arise.
> That's in transferring the lengthwise motion of the worm, along its axis,
> to shift the index arm to and fro. Backlash here can be minimised using
> some sort of spring, applying constant pressure in one direction or
> another, against an end-stop on the bearing of the worm-wheel. This will
> work as long as the overall friction of the arm is always dependably less
> than the pressure provided by that spring.

George

Excellent point.  My Astra IIIB uses spring tension to hold the worm gear in
position along its axis.  It is not adjustable, based on my inspection,
short of brute force.

Do you or other list contributors know what systems other sextants use to
control slop along the axis?

Bill

   

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