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Rennovating an 8-inch Cooke - Part 3

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#1 martinr

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Posted 16 September 2020 - 01:58 PM

Notes on dismantling the Polar Axis of the Bradfield Scope
In the last note I posted a long time ago, I noted the need for a gantry crane to lift the heavy items of the telescope out of their crates so I could work on them. I decided to build one out of lumber after watching a few useful (and some not so useful!) YouTube guides on design and construction.
It took until March of this year (and lots more time at home!) to finish building the crane. It’s not the most elegant of constructions, but it works really well, and fits beneath the open garage door by about 1-inch (that was close!). Two 4x4 uprights supported by cross bars, all bolted together securing  every potential flexure of the crane when a load is placed on it.

The first task was to lift the polar axis out of its crate and make a photographic record of its state and location of all the pieces. The Polar axis unit weights 234 lbs (106 kg). The pulley I used is rated for 1500 lbs so it’s an easy lift. The heaviest item I have is the Declination axis (400 lbs) and main base for the mount which is cast iron (478 lbs). Recall it was over a year since my last post – so this moment was long-awaited, and was very satisfying to finally be able to move these heavy loads around.

After cleaning up general debris around the polar axis that was collected over the years that the mount was sitting in a broken box, I spent some time thinking about next steps.

Little work was done during the summer since it reaches over 40° C (100°F) in the garage. In the past month temperatures have been more moderate, and I began removing items from the polar axis. Each of these items will be cleaned. The goal is to remove all brass fittings and then have the cast iron base cleaned professionally by the same local company that did the tube.

The polar axis has a large brace for fine adjustment and the iron bracket is extremely heavy. The device places pressure via a ball-bearing on the lower end of the polar axis. When the altitude adjustment bolts are loose, this should be an easy adjustment – but right now the adjustment bolts are firmly seated and will take some time with rust remover to loosen.

The polar axis has two worms and gears – one is for the telescope and the other is to simultaneously drive the RA setting circle. The lower RA setting circle was removed and the beautiful untouched surfaces on the inside are gleaming brass. Each piece was bagged and identified. Many identifying photos were taken to ensure the correct pieces go back  the correct place, and that all screws, nuts and bolts are identified.

The viewing reticle for reading RA was bent – it was removed and will be straightened and polished.

That’s the update for now. Enjoy the photos, which tell the main story

Attached Thumbnails

  • Lifting Polar Axis-IMG_3676.JPG
  • Polar Axis _removal of lower gear2-IMG_4068.JPG
  • Polar Axis _removal of lower gear5-IMG_4071.JPG
  • Polar Axis _removal of lower worm-IMG_4050.JPG
  • Polar Axis _Upper Gear1-IMG_4080.JPG
  • Polar Axis 3-IMG_3682.JPG
  • Polar Axis 2-IMG_3681.JPG

  • L. Regira, wfhixon, jim kuhns and 5 others like this

#2 wrnchhead

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Posted 16 September 2020 - 02:22 PM

Wow just re-read the other thread after forgetting all about it. As a fellow Kansan, I love that it's being worked on here. I also love the story of you bringing home the bed frame lol.gif we are cut from a similar cloth! When this beast is up and running, I hope you have it publicly accessible sometime, I would love to check it out. 


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#3 martinr

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Posted 19 September 2020 - 02:07 PM

For sure Eric, though it will be a while!




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