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    Re: Intended High Resolution Chronometer
    From: Brad Morris
    Date: 2014 Feb 26, 23:42 -0500

    Bill

    We may soon be able to resolve these topics with hard data.  A client of mine was unable to pay his invoice.  I offered to take a Nikon 6D Autocollimator (+ stand) and an Ultradex off his hands in exchange for the amount outstanding.  He agreed and the equipment is now in my hands.

    The Nikon 6D Autocollimator has direct resolution to 0.5 arc seconds and estimating 0.25 arc seconds is reasonably done. 

    We have discussed the Ultradex before.  Consider it a 360 sided polygon at 1° steps, each facet accurate to 0.5 seconds, repeatable to 0.05 arcseconds.

    New, this pair costs well over $40,000.00.  Its high resolution professional equipment.  For more details, just look online.  Fabulous kit.

    I'm in the process of selling off some collectibles to fund a surface plate, and some machined parts.  With those, I will easily be able calibrate sextant arcs. With an optical square and a dial indicator, I will be able to collimate the telescope to the sextant.  Once I have the kit complete, I will demonstrate it on youtube and offer these services to anyone at reasonable rates.  The National Physical Laboratory may be gone, but we are about to get something better!

    And yes, we will be able to measure gear lash, and see just how the preload reduces or eliminates it.  That can happen right now.  Approach some angle from one side.  Align the AC and zero it.  Approach that same angle (by micrometer only) from the other side.  Measure deviation with the AC.  Alas, I do not own a micrometer sextant. Both of my instruments are vernier type. Have you done this experiment Bill?

    Brad


    Brad,
    In the past like you I have advocated always approaching from the same side when using a micrometer sextant, but if adequately spring-loaded, it does not seem to matter to any detectable extent. Most micrometer mechanisms spring-load the worm against the rack (radial load) and the end of the worm against a solid abutment(axial load). Some do not have axial pre-load and rely on accurate fitting, e.g. some pre-WWII Hughes and Son, Filotechnica Salmoiraghi, Freiberger and SNO-T, and even these perform very well on the bench.

    Nevertheless, it is probably wise to approach a reading always from the same direction, preferably so the axial load is against a solid abutment rather than the spring and especially if the design has no axial preload spring.

    Bill Morris
    Pukenui
    New Zealand
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