Deforking a Celestron CPC 925



I have owned a Celestron CPC 925 for some time. It’s a great scope and good value for money. Over time, the only real negative for me has been the unwieldiness of the scope and fork arm assembly.

Not being the biggest or strongest bloke in the world, it’s become a chore to carry the scope and then the wedge down from upstairs. The law of averages dictate that one day I will trip and end up in a broken heap with the scope on top of me ;-).

I decided to bite the bullet and defork the OTA for mounting on a GEM. There didn’t seem to be too much information available for this specific scope, so this is my experience of the process.

You will need

  • A clean and stable area to work on the scope
  • A set of hex keys or hex screwdriver(s)
  • Something to shift stubborn screws like WD-40
  • Patience!

Before starting

It’s a good idea to remove any accessories from the scope that might get in the way or be at risk from getting broken.

Finally, a word of warning. This process is likely to be irreversible. Once you’ve separated the OTA, being able to remount it to the fork arms in a state that mirrors the one when it arrived from the factory is going to be tricky.

Deforking

You only need to loosen one fork arm in order to get the OTA free from the whole assembly. I worked on the side that holds the Nexstar hand control. E.g the arm that does not have the silver grab handle.

1. Remove the 4 capscrews that hold the OTA to the fork arms. There are 2 on each side.

OTA Screws

2. Remove the 6 screws holding the cover to the fork arm from the inside part of the arm (remember we’re working on the arm that has the slot for the hand control holder.).

There are 2 screws at the bottom of the arm, 2 in the middle and 2 near the top (which are quite fiddly to get at so you may want to reposition the OTA).

3. Remove the two screws at the base of the fork arm within the hand grab point.

Base Screws

4. Remove the small screw holding the clutch wheel in place. Then rotate the wheel anti-clockwise until it comes free.

Clutch Screw

The fork arm cover can now be removed (watch out for grease on the motor drive mechanism).

5. With the cover removed you’ll have access to the remaining 4 large screws at the base of the fork arm (located where the metal hand grab was). These hold the arm to the base casting.

My screws were locked down extremely tight, so I had to use some WD-40 to encourage them to move. I ended up using a hex torque wrench to untighten them.

With these screws removed, there’s enough play in the fork arm to remove the OTA. Be ready to support the weight of the OTA when it comes loose! I spread some soft pillows around the base of the arms just in case of mishaps.

If all goes well you’ll have a separated OTA like this.

Deforked CPC 925