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Bruce,

We used to just take a hacksaw and lop it off.

Ken
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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