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    Re: Site details
    From: Ken Gebhart
    Date: 2008 Nov 28, 22:38 -0600

    We used to just take a hacksaw and lop it off.
    On Nov 28, 2008, at 8:18 PM, bruce hamilton wrote:
    > Bill and Ken:
    > Thank you both for the information on my A10-A. It is missing some
    > bits,
    > like the mechanism to operate the pencil, but it does not matter to
    > me.
    > It has a bubble, but no adjustment, but fortunately it is the right
    > size. Perhaps when Bill's book comes out it will have enough detail
    > for
    > me to attempt to repair the bubble mechanism. The pin to remove the
    > mechanism cap looks soldered in so it could be a complicated job.
    > I am willing to give that screw a tweak to loosen the backlash
    > mechanism
    > as that is quick, but it wounds like a cleaning and re-lube is in
    > order.
    > I really like my A-10
    >  I spent a few years repairing mechanical Pentax cameras so I don't
    > mind
    > taking things apart, but I also know how badly things can go if you
    > don't have a manual. Unknown springs launch ball bearings into orbit,
    > never to be seen again.  I filled the bubble on my Mark IV, but it
    > was a
    > dream to open.
    > Speaking of which, my Mark IX has an averager but no cover. If I could
    > find a cover, I would love to keep it, but if I can't find a cover,
    > can
    > the mechanism be removed without much bother? I have all ready jumped
    > the wires so that the light works without the averager running.
    > Cheers
    > Bruce
    > Ken Gebhart wrote:
    >> What Bill says is true, but the backlash spring was designed to be
    >> too weak.  The A10 and A10A were known as the "backlash sextant"  by
    >> old air navigators.  Backlash would creep in after even a short
    >> period of time with the lubricants then being used.  There is an
    >> accessable screw under the averager plate that was often turned a
    >> little CCW to loosen things up and restore backlash free operation as
    >> a quick fix.
    >> Ken Gebhart
    >> On Nov 28, 2008, at 1:15 PM, engineer wrote:
    >>> Bruce
    >>> There shouldn't be any backlash with an A10, as it is provided
    >>> with a
    >>> backlash spring. The index bearing after 60-odd years is often in
    >>> need
    >>> of lubrication to ensure free movement (I once had one completely
    >>> seized). The bearing can be difficult to pull apart and reassembling
    >>> with the anti-backlash spring correctly tensioned can be a trying
    >>> exercise. You can probably improve the index error by setting the
    >>> instrument to a sea horizon, removing the read-out counter,
    >>> setting it
    >>> to zero (allowing for dip) and replacing.
    >>> I will be covering these and other details in an e-book on A10
    >>> restoration, due out at the end of February. It will be along the
    >>> lines of my e-books on the reconditioning of the Mark IX series
    >>> bubble
    >>> sextant and my "Naked Nautical Sextant". See www.sextantbook.com for
    >>> details. Meanwhile, you can contact me off line about your A10 if
    >>> you
    >>> wish.
    >>> Bill Morris
    >>> On Nov 28, 4:08 pm, bruce hamilton  wrote:
    >>>> All times GMT 27 Nov 2008
    >>>> A-10 Sextant with 31.5' index error off the arc (horizon reading
    >>>> is lees
    >>>> than zero in case if am mixed up)
    >>>> Sextant has no other calibration. I frequently get LOP's within 2
    >>>> miles
    >>>> of my AP so I am happy. It has backlash so I try not to change
    >>>> directions.  I suspect some other error as stars with higher
    >>>> altitudes
    >>>> tend to give me bigger errors.
    >>>> I am actually quite surprised that I am getting a fix that is close
    >>>> enough to find the airport (or Bermuda) if I had do. I have an
    >>>> A-12 and
    >>>> Mark IX, but I only drag out one an evening.
    >>>> Thanks
    >>>> I am presently using CelestNav 3.0 for the palm pilot to work
    >>>> out the
    >>>> sites. I would appreciate any comments on the program. I like it
    >>>> for
    >>>> everything but the fix calculation, but I think 3.0 is only a Beta.
    >>>> AP 49d  16.1 N  123d 7.1 W
    >>>> Pollux   06:19:33   27d  59.3'
    >>>> Vega    06:16:31   13d    0.3'
    >>>> Betelg   06:10:53   28d  44.3'
    >>>> Altair    03:56:11   22d  37.0'
    >>>> Vega    03:54:45   32d  06.9
    >>>> Capella 03:52:46   39d  35.7'
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