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Parks Optical Observatory GEM for 12.5" Newtonian

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#1 JimRitt

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Posted 02 August 2021 - 10:40 AM

I recently acquired a property with a 15' ProDome that contains a 12.5" Parks Optical observatory series Newtonian scope and GEM.  The clock drive has a cracked hub gear.  Does anyone know if there is a source of replacement parts for this since Parks optical is no longer around?  i have attached a picture of the crack which is right where the set screw secures the hub gear to the RA shaft..  Don't know if it is possible to repair this or if there is a compatible clock drive replacement available?  Also may consider a new "go to" mount if I can not repair the clock drive;  so any suggestions for repair, or options for replacement of clock drive, or recommendations for a reasonably priced go to mount for this scope would be appreciated!

 

Thanks - Jim

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  • cracked hub gear.jpg

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#2 Couder

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Posted 02 August 2021 - 10:44 AM

That piece should not be difficult to make. I would think any machine shop could do it. 


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#3 siriusandthepup

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Posted 02 August 2021 - 11:16 AM

 

That piece should not be difficult to make. I would think any machine shop could do it.

+1

 

It also may be repairable with some skilled welding and a little clean up machining. Ask the machinist for his recommend.


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#4 rob1986

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Posted 02 August 2021 - 11:58 AM

can we get pictures of the scope and mount? flowerred.gif


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#5 ram812

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Posted 02 August 2021 - 12:26 PM

  Welcome to CNwelcome.gif ! Machine shop! It looks like the shaft also has a series of cracks? Musta' been a lot of torquing going on there. +👍 to rob1986, pics would be neat! Great grab, at any rate. Now why didn't I buy a place with an obsey already built? 

Good luck and CS, Ralph


Edited by ram812, 02 August 2021 - 12:31 PM.


#6 macdonjh

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Posted 02 August 2021 - 02:58 PM

I'm not making any recommendations until pictures are posted.

 

Those hubs have to be standard.  If you can take good measurements (using calipers, not a measuring tape) you should be able to contact any company which supplies bearing and sheaves about that hub.  I'll bet somebody still makes one with the dimensions you need.



#7 JimRitt

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Posted 02 August 2021 - 05:37 PM

Thanks for the encouraging comments regarding machining a new part!  I spent some time with it today and I think it may still be functional.  I rebalanced the scope, loosened the set screws and rotated the hub gear around the shaft to a different spot, and adjusted the clutch tension on the hub gear.  There now seems to be pretty even tension when I manually rotate the scope on the RA axis.  Ran the drive for about an hour and the scope seemed to move fine although I'll need a clear night now to see how well it is tracking and if the mount is even close to being aligned properly.  Here are a few pics of the observatory, scope, mount, and drive.  Was lucky to find a place that already had an observatory, especially since we are totally off grid running everything on solar.  The place had been empty for about 15 years.  The dome still works fine with fully powered shutter and dome rotation, although i did have to replace a rectifier in the power supply and get a locksmith to make a key so i could get into the observatory!

Attached Thumbnails

  • observatory 1.jpg
  • telescope 1.jpg
  • mount.jpg
  • clock drive.jpg

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#8 siriusandthepup

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Posted 03 August 2021 - 09:00 AM

Very nice!

 

Forgot to say "Grats" on the new real estate acquisition. Sweet!  Great sized observatory and a nice telescope too.

 

waytogo.gif



#9 SteveGR

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Posted 03 August 2021 - 01:35 PM

Now that's a find!  With everything else they put into it, I wonder why the builder didn't put in a permanent pier?  Probably one of those unanswerable questions at this point. smile.gif



#10 JimRitt

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Posted 03 August 2021 - 04:04 PM

Don't know why they would not have put in a proper pier that is isolated from the rest of the floor.  Looks like they just went with the Parks observatory package which included the scope and the mount. From what I can tell it was purchased around 1998 and used until about 2005 after which the whole thing was mothballed until now.  The owner from 2006 until we bought it hardly ever came to the property and never used the observatory.



#11 Sean Cunneen

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Posted 03 August 2021 - 04:22 PM

It looks like the drive will work as is, if you would like to get it replaced, you'll have to get a whole new drive, either Mathis or Opticraft are places to start. If you have a machine shop make a new collar the cost between that job and getting the entire drive replaced would be very close to each other.

#12 SteveGR

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Posted 04 August 2021 - 01:36 PM

Don't know why they would not have put in a proper pier that is isolated from the rest of the floor.  Looks like they just went with the Parks observatory package which included the scope and the mount. From what I can tell it was purchased around 1998 and used until about 2005 after which the whole thing was mothballed until now.  The owner from 2006 until we bought it hardly ever came to the property and never used the observatory.

They may have been purely visual, and if they observed by themselves or in a small group, it wouldn't have been very limiting.  Are you planning to use it as is?  Or do you plan to modify it?
 



#13 JimRitt

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Posted 06 August 2021 - 12:06 PM

They may have been purely visual, and if they observed by themselves or in a small group, it wouldn't have been very limiting.  Are you planning to use it as is?  Or do you plan to modify it?
 

i will use as is at first but eventually I may replace it with a pier and "go to" mount



#14 JimRitt

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Posted 07 August 2021 - 12:03 AM

The cracked hub gear assembly is going to the machine shop on Monday.  Going to see if we can fabricate a new insert to replace the cracked composite insert.  I have partially dismantled the gear assembly to see how it works.  It is basically made up of a brass gear ring that nests onto a composite part.  The gear is basically sandwiched between the composite and a metal component.  There is also some type of plastic/nylon ring that must serve as a clutch plate.  The assembly is held together by tensioner bolts that allow for adjustment of the clutch resistance.  Pictures below show: 

- crack in composite component of assembly

- bottom view of hub gear assembly

- top view of hub gear assembly

- hub gear assembly partially dismantled

- hub gear assembly on the RA axis

 

I was not able to easily separate the brass gear from the composite piece so i will leave that to the machine shop.  Did not want to risk damaging the gear ring.

 

Attached Thumbnails

  • crack in composite insert.jpg
  • bottom view od hub gear assembly.jpg
  • top view of hub gear assembly.jpg
  • hub gear assembly partially disassembled.jpg
  • hub gear on RA axia.jpg


#15 bjkaras

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Posted 07 August 2021 - 01:17 AM

i will use as is at first but eventually I may replace it with a pier and "go to" mount

I’d keep the mount, it’s a nice one. That’s what I use for my 10”. Get an Argo Navis and you have a nice “push to” system.


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#16 JimRitt

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Posted 07 August 2021 - 11:38 PM

I’d keep the mount, it’s a nice one. That’s what I use for my 10”. Get an Argo Navis and you have a nice “push to” system.

the scope is currently set up with encoders for the JMI  NGC Max system which I think is similar to the ArgoNavis



#17 Taylor

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Posted 08 August 2021 - 08:26 AM

Wow, that's a great piece of property you acquired! 

 

Hard to believe someone installed that nice observatory and that scope/mount combo and just stopped using it. 

 

There is a system called OnStep that would allow you to add GoTo capabilities to that mount. https://onstep.group.../main/wiki/3860


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#18 SteveGR

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Posted 09 August 2021 - 01:05 PM

Do you know the focal length of the scope?  I looked up that series on Parks zombie website, and the one they were selling at the end was a F5, is that what yours is?


Edited by SteveGR, 09 August 2021 - 01:48 PM.


#19 photoracer18

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Posted 09 August 2021 - 04:20 PM

Wow, that's a great piece of property you acquired! 

 

Hard to believe someone installed that nice observatory and that scope/mount combo and just stopped using it. 

 

There is a system called OnStep that would allow you to add GoTo capabilities to that mount. https://onstep.group.../main/wiki/3860

Yeah but to do that he needs to come up with a complete other worm drive for the DEC axis as that has a tangent arm DEC drive. If that is using a DC 12v DEC drive its easy to find a dual axis drive corrector on the used market that will power both current axis drives.


Edited by photoracer18, 09 August 2021 - 04:21 PM.

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#20 JimRitt

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Posted 09 August 2021 - 06:36 PM

that is correct.  It currently has a tangent arm drive that is controlled by a hand held controller that allows adjustments to both the DEC and RA axes.  Both axes have encoders that are tied into an NGC Max for manual pointing via the digital setting circles.  Not familiar with dual axis drive correctors so will need to read up on it.  Would love to convert this to a go to system.



#21 JimRitt

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Posted 09 August 2021 - 06:59 PM

dec drive corrector.png

Yeah but to do that he needs to come up with a complete other worm drive for the DEC axis as that has a tangent arm DEC drive. If that is using a DC 12v DEC drive its easy to find a dual axis drive corrector on the used market that will power both current axis drives.

 

 

that is correct.  It currently has a tangent arm drive that is controlled by a hand held controller that allows adjustments to both the DEC and RA axes.  Both axes have encoders that are tied into an NGC Max for manual pointing via the digital setting circles.  Not familiar with dual axis drive correctors so will need to read up on it.  Would love to convert this to a go to system.

this pic shows the dec drive, tangent arm, and dec motor on the right end of the threaded drive



#22 John Fitzgerald

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Posted 09 August 2021 - 07:19 PM

How are the mirror coatings after this long?



#23 JimRitt

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Posted 10 August 2021 - 09:22 AM

Both mirrors were pretty coated with grime so I took them both out and cleaned them and collimated the scope.  The coatings look good visually but I have not had a good clear sky yet to check out the performance.  There has been a lot of smoke and haze here from the forest fires!  I hope this week we will get some decent skies.



#24 photoracer18

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Posted 10 August 2021 - 02:08 PM

that is correct.  It currently has a tangent arm drive that is controlled by a hand held controller that allows adjustments to both the DEC and RA axes.  Both axes have encoders that are tied into an NGC Max for manual pointing via the digital setting circles.  Not familiar with dual axis drive correctors so will need to read up on it.  Would love to convert this to a go to system.

The main problem with converting an older style GEM with RA worm and DEC tangent is where to put the DEC worm drive. It can always go on the top of the CW shaft side of the axis and sometimes it can go where the Tangent arm is. You don't want to put it in the upper position and have to push the saddle end farther above the RA axis as it can make balancing harder and require more weight on the CW shaft. Sometimes you can just put the main drive gear right where the tangent arm was and mount the worm bracket and motor to the bottom of the cradle or saddle. That s the way most modern GEM mounts are. However most conversions of older GEMs I have seen put the DEC drive on the bottom position below the DEC housing. But in your case you would have to remove the DEC encoder. Not a big deal when you are converting to go-to. I just think it looks better above the DEC housing. I bought a Byers 7" Starmaster many years ago intending to convert the modified DS-16 I got from the late Dr. Green(e) when I bought his 6" Jaegers F15. It already had a Byers 11.3" drive on the RA axis driven but the original DC motor powered tangent arm on the DEC all wired into a Byers controller box. I also have a Schaefer AT-9 that has a tangent arm DEC, plus it has a payload of at least 75 kg. I would just need to have the Byers 7" clutch bored out from 1.5" to 1.75" and then buy a couple of Onstep compatible hybrid steppers. But that only if I get a place to build an observatory.

 

My feeling is if you are considering the slightest chance of doing this then if a Byers drive with a chutch of the correct shaft diameter for your mount comes up for sale buy it because making one as good will cost even more and you can always sell it for what you got in it.


Edited by photoracer18, 10 August 2021 - 02:12 PM.

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#25 JimRitt

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Posted 10 August 2021 - 03:57 PM

Brought hub gear to the machine shop and they separated the gear ring from the composite part.  Picture shows the side of the composite piece that the gear sat on and the shelf that it nested in.  The composite piece has 20 holes (not counting the set screw holes) even though only 6 are used.  Not sure why unless they were used during the manufacturing process or maybe the part was also used for other applications.  The replacement part will be milled out of a block of Delrin and will hopefully be done this week.  Will be interesting to see if the clutch works okay with the Delrin as I think this will have less friction than the composite material.  We'll see![attachment=1846401:composite piece showing shelf.jpg

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  • composite piece showing shelf.jpg

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