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CPC 925 GPS: Replacing rear cell SCT adaptor with Baader 2” ClickLock

Celestron accessories equipment
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#1 Visit-the-Moon

Visit-the-Moon

    Sputnik

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Posted 01 July 2020 - 03:01 AM

After watching this forum for years I’ve finally joined, my 1st post.

 

I replaced the original rear cell SCT adaptor on my CPC 925 with the far more useful Baader 2” ClickLock SC-Clamp and thought I’d share how I approached the problem. 

 

After over 12 years of use the male thread on the adaptor is quite worn - it is simply a 14 mm spacer albeit a solid one. The hole in the side of the SCT spacer is not a punch point nor for a grub screw, it takes the pin of a pin or hook wrench used to tighten beast. The spacer is bonded into place permanently with red Loctite or a similar product meaning that its removal is not straightforward. You risk damaging the telescope if you rely on brute force! Red Loctite polymerises within the thread, it cannot be dissolved with typical solvents. Methylene chloride will dissolve the polymer but it is a toxic solvent that will also damage all the paint on the telescope. Henkel who produce Loctite recommend heating to 450F/232C to soften the polymer. Online automotive videos showing removal of bonded nuts and bolts typically use a gas torch, not a good idea.

 

I heated the SCT spacer on the assembled telescope with an electric heat gun set to 600 C, having removed any parts that could be affected. It is never a good idea to do the pilot run on the telescope. To test, I heated a spare 42mm T adaptor to 250 C to ensure heating would not damage the threads – measuring the temperature with an IR thermometer. After cooling, the thread was not deformed. No problem. Next I used red Loctite to bond a ½” nut and bolt together and let it cure to full strength. This was not possible to budge with a large spanner, but when heated to 150 C with the heat gun, I could remove the nut with just a little force.

 

So now the telescope. I heated the rear spacer for 5 min. I could not reach 150 C, but hit 125 C. Using locking grove pliers typically used for plumbing, I could rotate the adaptor a few mm before it cooled to below 125 C. After a few rounds of heating and applying force, the spacer could then be unscrewed. The "SCT" thread on each side is 2”, 24 threads/inch, as I said it is just a spacer. Much of the charred Loctite could be dissolved from the rear thread with acetone, taking care not to damage the surrounding paint. The remaining residue could be cleaned out of the thread with a sharp scalpel. Using isopropyl alcohol as a lubricant, I ran a female SCT thread over the freshly exposed male thread on the back of the telescope to clean it up. Came out nicely. The Baader 2” ClickLock SC-Clamp screwed on snugly, works like a champ.

 

When I’m satisfied that I’ll commit to the Baader, I will probably bond it in place with the weaker medium strength blue Loctite, which can be removed with regular hand tools.


Edited by Visit-the-Moon, 01 July 2020 - 04:42 AM.

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#2 pyrasanth

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Posted 01 July 2020 - 04:00 AM

I gave up reading your post- I'm sure it is interesting. However the lack of paragraphs makes it really difficult to digest all the information.

 

Please help us to help you- paragraphs are very much necessary!


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#3 Visit-the-Moon

Visit-the-Moon

    Sputnik

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Posted 04 July 2020 - 01:59 AM

The Baader 2" ClickLock fitted.

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