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Comet Catcher Sled Focuser Knob Replacement?

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6 replies to this topic

#1 KerryR

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Posted 15 February 2019 - 04:45 PM

Hi all,

Has anyone found a replacement knob for the Celestron/Vixen sled focusers? There are a couple of versions of this focuser. Mine's a later version, threaded inside and has a set screw to hold it in place.

I'm restoring a Comet Catcher, and the stock knob split in half due to strain from the set screw...

I posted in the ATM section, but no joy. 

Cheers,

Kerry


Edited by KerryR, 15 February 2019 - 04:46 PM.


#2 clamchip

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Posted 15 February 2019 - 07:22 PM

I ended up using a old radio knob, slips on with a set screw in the side.

The dust is 'as purchased' thats what happens sometimes:                                                                                                              corner of the living room>bedroom closet>garage next to the bowflex>craigslist>happy new owner                                                                                                                                                                                                                                                 Robert

 

post-50896-0-24928900-1549485348.jpg


Edited by clamchip, 15 February 2019 - 07:31 PM.

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#3 apfever

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Posted 15 February 2019 - 09:16 PM

you can fix that knob.  see if pictures.  dang hang on for an edit

 

found this old picture, for starters, check to see if you have a brass or plastic gear before you get too dedicated.

I have a picture of a clamp repair that might work a miracle.

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Edited by apfever, 15 February 2019 - 09:23 PM.


#4 apfever

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Posted 15 February 2019 - 09:41 PM

Here's the repair.  There is a standard auto hose clamp that fits the knob collar perfectly. The set screw aligns with the groove in the clamp by chance and just clears for going in or out. The set screw can be installed or removed once the clamp is in place.  The tangs on the clamp will hit the focuser body when rotated.  I used a Dremel and cutting wafer stone to cut the tangs off as seen on the installed unit. This might hold your split knob back together.  Also, carefully check ABS plumbing cement to see if it melts the plastic. I can't remember if it works or not, but if so you can very c-a-r-e-fully and sparingly use the cement to assist.  A drop too much and you'll melt the knob into a mess - if it's ABS plastic.  

 

One of these two knobs is an actual repair of the set screw hole, the other is preventive maintenance. I don't remember which is which.

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#5 KerryR

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Posted 15 February 2019 - 10:22 PM

Thanks for the suggestions, guys! Much appreciated.

Gives me some hope for rescuing this focuser.

Mine's a black gear, so... plastic?? I'm shocked this has worked as long as it has.

I have 2 of these focusers, one is on a Vixen 6" f5, the other on the comet catcher. I've switched bits and pieces between the 2 scopes, so I no longer really know which sled goes with which scope.


 



#6 apfever

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Posted 19 February 2019 - 07:51 AM

This knob is kind of complicated with quite a few internal parts.  The position of the gear contact on the rack can be adjusted so that you use a fresher part of the gear, should the gear be worn.  I've had a few apart but don't remember the layout.  You don't need to shim the whole bracket off the focuser body, you can reposition the gear and shaft assembly within the knob unit.  I've done it to make chewed up plastic gears work fine on fresh teeth.  You'll have to take the knob apart and lay out the pieces in an exploded fashion, keep track, and use common horse sense to see how the gear can be repositioned if needed.

 

This will require removing the face plate off the knob, which is glued on, more like taped on as in a sticky back label.  I've always managed to pry one off without tearing it up.


Edited by apfever, 19 February 2019 - 07:54 AM.


#7 KerryR

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Posted 19 February 2019 - 01:43 PM

This knob is kind of complicated with quite a few internal parts.  The position of the gear contact on the rack can be adjusted so that you use a fresher part of the gear, should the gear be worn.  I've had a few apart but don't remember the layout.  You don't need to shim the whole bracket off the focuser body, you can reposition the gear and shaft assembly within the knob unit.  I've done it to make chewed up plastic gears work fine on fresh teeth.  You'll have to take the knob apart and lay out the pieces in an exploded fashion, keep track, and use common horse sense to see how the gear can be repositioned if needed.

 

This will require removing the face plate off the knob, which is glued on, more like taped on as in a sticky back label.  I've always managed to pry one off without tearing it up.

My issue is that the plastic knob is split in half, currently held together only by the aluminum face plate. The rack and pinion are fine, as is the overall movement of the sled. Because the knob is split, I can't thread it on to the pinion shaft with sufficient tension, and I can't tighten the grub screw because doing so only further splits the knob. Your solution with the clamp should solve the problem... if I can find one.




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