Re: [APML] G-11; Results of gear lapping and overhaul

["Franklin A. Holub" <lists@my-spot.com>]

Hi Glen,

After I received my second hand G-11 about three years ago I couldn't get
the ST-4 to guide well with exposures of more then 1 second. Finally, after
about 6 months, I lapped my RA worm gear. I had 7 "massive" cycles per worm
revolution of +/-8 asecs before lapping and a nice manageable curve of +/-4
asecs after lapping.  You can see those PE curves here...

http://www.my-spot.com/PE-lapping.pdf

About a year later Scott Losmandy sent me one of his "experimental" high
precision worm gears. It did not reduce the total PE but boy was it smooth!
See...

http://www.my-spot.com/pe.pdf

Just a couple of suggestions. Most folks using a G-11 have the OTA on the
"west". Also make sure that you have the counterweights a bit heavy on the
"east". That is, when you loosen the clutch, the counterweights (on the east
side of the mount) drop slowly.
Also, I called Scott one day and asked him why my mount seemed to run fast
(or was it slow?). He said that most of the time it had to do with setting
the mount on the dirt or in the yard - the feet were sinking - slowly. For
my next tracking run, I put the mount on my paved driveway. Sure enough, the
tracking speed was near to perfect. However, for the last year, my mount has
been permanently mounted, and the tracking speed is still off - go figure.

Anyway, now-a-days, I can track at 1200mm for 3 seconds with no more then a
couple A2 or A3's per worm cycle.

Frank

----- Original Message ----- 
From: "Glenn Ray" <glennlray@mail.ev1.net>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Thursday, January 22, 2004 2:41 PM
Subject: [APML] G-11; Results of gear lapping and overhaul


> For Y'all's Info:
>
> Well, after some reassuring advice from Dan Norman, Stu Travelbee,
> and Richard Crisp (THANKS, Guys!), I decided to lap the RA gear
> myself (gulp).  I used 1 micron Luster-Lap (from McMaster-Carr);
> ran the drive at 16x for 4 revolutions.  Also re-lubed all needle
> & thrust bearings.
>
> My previous PE was +/- 8", with strong swings >4 arcsec/sec.  This
> made it difficult to guide at anything less than 2x, or very short
> exposures.
>
> Last night I ran a preliminary tracking test (ST-4, guiding at
> 2032mm and tracking stars near meridian/equator).  I used CCDTRACK
> to record the tracking data (it outputs to a log file) and plugged
> the results into Excel.
>
> Summary:
> 1) Total PE has been reduced to +/- 4 arcseconds.
> 2) Each revolution of the worm (4 mins) has three cycles of error
> with peak-to-peak of about 4-5 arcseconds each.
> 3) There is a total RA drift about 75 arcseconds per hour (too
> fast).
>
> While I'm happy about cutting the overall PE in half, I'm
> perplexed about the other two findings.  I can't imagine a
> physical scenario that would cause the quick cycles.  Because I
> only did a rough drift alignment (N-S okay, but E-W a little off),
> I wonder if RA showed a component of that alignment error.
>
> I really suspect both are related to electronics, but can't
> confirm that until I do another run.  I noted several people on
> the Internet who noted similar RA drift, but no answers.
>
> After performing a second run, I plan to post an article with
> procedures and results on my website.  I also will investigate
> using PEC to try and smooth it further.  I will welcome any
> suggestions or additional information.
>
> Thanks,
>
> Glenn Ray
> Cypress, TX
> http://users3.ev1.net/~glennlray/Astro
>
>
>
> >> >----- Original Message ----- 
> >> >From: "glennlray" <glennlray@mail.ev1.net>
> >> >To: <astro-photo@seds.org>
> >> >Sent: Wednesday, January 07, 2004 2:28 AM
> >> >Subject: [APML] Semi-OT: Precision Machine Shops in Houston
> area?
> >> >
> >> >
> >> >> I am considering having the RA gear on my G-11 lapped and am
> looking
> >for a
> >> >good precision machine shop in the Houston, Texas area.  I may
> consider
> >> >companies outside of Houston if none can be found here.  I
> don't think I
> >can
> >> >lap the gear myself, unless someone here convinces me I can.
> >> >>
> >> >> Please reply off-list.
> >> >>
> >> >> Thanks,
> >> >>
> >> >> Glenn Ray
> >> >> http://users3.ev1.net/~glennlray/Astro
> >> >>
> >> >>
> >> >>
> >> >>
> >> >> _______________________________________________
> >> >> Astro-Photo mailing list
> >> >> Astro-Photo@seds.org
> >> >> http://seds.org/mailman/listinfo/astro-photo
> >> >>
> >> >
> >> >
> >>
> >
> >
>
>
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>
>
>
>
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