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[gingerbreadassassin]

Greetings!

 

At an estate sale, I purchased two observatory domes and their contents. One was mostly empty, but the other contained a 16" F8.4 RCT produced by Optical Guidance Systems back in the '90s.

 

 

 

As I will be traveling soon and the estate is due to be on the market soon, I need to empty out and disassemble the observatories. As part of the purchase, I was handed a stack of documentation, but besides the interferogram from when the primary was refigured and recoated (in 2000), I have no materials related to the OTA itself. I am in contact with OGS and am waiting to see if they have any legacy documentation available. While I have a fork-mounted C11, I have never worked with a scope as large or valuable as this, and am trying to put together a plan of attack to disassemble it. As you can see, the interior coating of the OTA is flaking off, and I have no clue what other debris might be in there, threatening to fall on the mirrors should I attempt to move it as assembled.

 

 

Therefore, I'm thinking I want to disassemble it as much as possible (at the very least removing the primary mirror) while still mounted. Note the mount seems to lack any sort of clutch mechanism. Rather, it seems that to move the scope manually requires dis-engagement of the worm drives. This is incorrect, lifted from the manual that I have for a GT-1100; there are knurled rings on the faces of each drive gear that adjust the clutch. The same (or nearly identical) mechanisms exist for both DEC and RA:

 

 

My rough-draft strategy is this:

 

1. Position OTA/mount for disassembly
  a. Disengage DEC worm gear from spur clutch

  b. Rotate DEC so OTA is pointed near the equator (as pictured, some distance from the eastern horizon as well)

  c. Re-engage DEC worm gear clutch

  d. Anchor RA with barely-taut ratchet straps on both east and west sides (note: I do NOT know the current balance situation, hence my precaution here)

  e. Disengage RA worm gear from spur clutch

  f. Check that balance in RA is slightly OTA-heavy
  g. Rotate RA counter-clockwise (primary remains on top to avoid debris falling on it) so that OTA is inverted (counterweights + shaft straight above, OTA pointing at western horizon. Intentional weight imbalance from step f should help here)
  h. Re-engage RA worm gear clutch?

  i. Possibly use ratchet straps to anchor RA in East/West to the dome?
2. Disassemble OTA
  a. Remove guide/spotting scopes

  b. Remove focuser

  c. Remove primary cell

    i. It seems there are 4 screws around the OTA that hold the primary cell in place, each circled in this image

    ii. The three circled in red should be relatively easy to remove

    iii. The one circled in green looks to be covered by the mounting plate. Hopefully, simply hiding underneath the balancing weight. I think I'll try to access this one first. If I'm unable, I suppose I'll have to remove the OTA from the mount

  d. Remove primary from the cell

  e. Store mirror in transport box ( what precautions should I take to protect the primary in the box? Should I clean it before storage? )

  f. Replace primary cell in OTA

 

3. Remove OTA from mount

  a. Position desk/table underneath OTA

  b. Find some way to stabilize OTA on table (I may fashion something from some spare framing lumber)

  c. Un-fasten bolts securing OTA to mount

  d. Roll OTA and table away from mount

4. Position mount at rest for disassembly

  a. Disengage RA worm clutch

  b. Loosen either east or west ratchet strap, whichever the counterweights lean towards

  c. Slowly, carefully rotate RA opposite its current lean, until RA comes to rest with counterweight shaft pointing downwards.

 

I do have a manual that, according to OGS, should be 95% accurate for the mount. It has instructions for unboxing and set-up, which I will follow in reverse order to disassemble the mount. Once disassembled, this scope in particular will likely remain so for a year at least; I will be a new parent soon, so it will be a while before I'm ready to return this behemoth to service. Anyways, I think I've covered just about everything as far as OTA disassembly and removal goes. But please, if I've missed anything or should modify my approach in any way, do comment and leave feedback.

 

Thanks in advance!

Edited by gingerbreadassassin, 14 August 2024 - 12:06 PM.

[gingerbreadassassin]

Got a response from OGS:

 

We looked at your posting. The 16" RC looks similar to ours, but not sure that is one that we built!  We might have rebuilt one that someone else constructed? The control system is first generation Software Bisque and it was very slow. The mount is old and uses Mathis gears. There are clutches on the gears. The knurled ring on the face of the gear adjusts the clutch. NEVER disengage the worm from the worm wheel. The tolerance and alignment between the two is very difficult to get correct.

 

We will research this some more.

Well then, I'm glad I asked! I believe I can indeed spot the knurled rings on the gear faces, behind the windows:

 

But I guess I found part of that 5% of the manual that isn't accurate:

There is no clutching mechanism on the Paramount. This means that balance is achieved by disengaging the worm from the gear in each axis

As for the OTA, it has an OGS sticker on it, but I suppose that could've been lifted from another piece of equipment.

 

Will keep this thread updated