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Loosening a Frozen Declination Brake

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#1 Gregory Gross

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Posted 26 February 2019 - 11:00 PM

In addition to the discussion in this archived CN thread entitled "Frozen Declination Brake" and this CN posting, I wanted to share my story about unfreezing the declination brake on an early 1960s Questar that I recently acquired with the hope that others who have the same problem can benefit from this knowledge.

When I received my Questar, the declination brake was frozen in place in spite of every effort I made to turn the brake knob clockwise (remember that the loosening and tightening motions are opposite to what one might expect).

I first removed the brake knob. By sheer stroke of luck, the small Bristol wrench that would have accompanied this scope was still hanging out in the solar filter pouch. (See this CN thread entitled "Hex wrench for side knobs" for details.) Bristol wrench in hand, I loosened the set screws and removed the brake knob. I then cleaned up the threads and dropped conservative amounts of Liquid Wrench penetrating oil around the point where the brake screw threads meet the side arm on the outside and around the screw head on the inside of the side arm. I used the pointed end of a pin to pick up a small amount of oil and drop it in the desired areas, being careful to observe the a-little-goes-a-long-way rule. But after letting the oil really soak in overnight, I was still unsuccessful with getting the brake to loosen the following morning.

Fearing that I would have to send my Questar in for service, I then remembered the two-nut trick that one can use to loosen a screw from the opposite end of a screw head. Threading in one nut just short of making contact with the side arm and then tightening a second nut against the first, I could then use a wrench to apply more torque than what I could manage with my bare hand using the brake knob. The key lies in using nuts with the decidedly non-standard 8-36 threading (one typically finds machine screws and nuts with 8-32 threads at the local hardware store). Receiving an order of 8-36 nuts from Grainger, I proceeded to apply two nuts as follows:

DeclinationBrakeScrew


With a box wrench around the outer nut, I slowly and gently applied more and more torque, again, in a clockwise motion until... it... finally... loosened. Success!

In hindsight, I may not have had to use penetrating oil, but now I have a well-lubricated declination brake, so I suppose using it was not the worst thing in the world.

Many thanks to Ben Langlotz (Optics Patent) for cluing me in on the fact that declination brake screws have non-standard 8-36 threading. That little bit of information saved me a ton of time, headache, and frustration with finding the properly threaded nuts.
  • astro140, Wisconsin Steve, rcwolpert and 2 others like this

#2 Optics Patent

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Posted 26 February 2019 - 11:41 PM

Bravo!


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