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Focuser stuck on scope

Highburymark

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Highburymark

Highburymark

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I've just bought a very lovely Moonlite focuser for my Lunt 50 solar scope (thanks to Jabeoo for a beautifully packaged delivery), but I have a problem. The stock helical focuser will not unscrew from the scope.

It will unscrew a couple of turns so there's a small gap between the focuser and the ota (see pic) but then it seizes up. Stronger people than me have tried to loosen it but with no luck.

Does anyone have any advice?

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Highburymark

Highburymark

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Excellent SGL response as always. Thanks. 

The inner tube of the focuser (with the grub screw) has already been removed. - see pic. It's the remaining part of the focuser that I can't shift.

Knighty - Thought about wd40 but frankly not sure where to apply it.

 

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Knighty2112

Knighty2112

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Did the focuser turn easily for the first two turns before it became stuck? If it did have a grub screw locking it down too I doubt you would be able to turn it two times in the first place, unless the grub screw wasn't fully tightened down and it has now caused a problem on the screw thread on the focuser perhaps. Hoping not the later, as if the thread has been damaged too then that will be a pain to sort out! :( 

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DRT

DRT

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I've just dismantled mine very easily - no need to remove the grub screw as that only holds the two parts of the focuser together.

The focuser has a male thread that goes into a female thread on the red section of the OTA. These threads are very fine and it is possible they have been cross-threaded :sad:

Have you tried screwing it back on and then gently unscrewing? If it is cross threaded you might be able to get it back in line.

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Highburymark

Highburymark

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Yes I have tried that Derek - it screws back in very smoothly - just gets to a point in opposite direction where it seizes up. But actually your photos are useful - I didn't know precisely how they connected before.

But I've just taken the rubber grip off and there are 3 tiny screws (one pictured) - shame I don't have the tools to tackle them tonight, but am hopeful this might do the trick. Appreciate all the help.

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DRT

DRT

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If the thread screws back in easily I think you should try WD40. Unscrew the focuser from the OTA as far as it will go and then spray a little WD40 onto the black male thread in the gap between the focuser and the OTA. Then screw the focuser in and out a few times to see if it releases the jam.

I think those little screws will be part of the helical focuser assembly and not connected to the OTA as they are too far away from the join. The thread that attaches to the OTA is only about 3mm long. From the first picture you posted it looks like you have it unscrewed almost to the end with only 1mm or so to go!

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Highburymark

Highburymark

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1 hour ago, DRT said:

If the thread screws back in easily I think you should try WD40. Unscrew the focuser from the OTA as far as it will go and then spray a little WD40 onto the black male thread in the gap between the focuser and the OTA. Then screw the focuser in and out a few times to see if it releases the jam.

I think those little screws will be part of the helical focuser assembly and not connected to the OTA as they are too far away from the join. The thread that attaches to the OTA is only about 3mm long. From the first picture you posted it looks like you have it unscrewed almost to the end with only 1mm or so to go!

Thanks for the advice Derek - really useful.

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Zakalwe

Zakalwe

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Screw it back in and then out. Keep nudging it gently past the stuck point. It sounds like a damaged thread or a bit of grit stuck in a thread. If you go at it like a bull in a china shop then you will cause it to bind.


Be careful with the WD40...it's nature is to creep and it outgasses a lot. if you get it on the glass that is right up to the back of the focuser then it could be a pig to clean off (isopropyl alcohol will be needed). I'd only start spraying it as a very, very last resort. If the scope is in warranty then I'd be speaking to the retailer.

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cardigan wearer

cardigan wearer

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I agree with the wd40 seeping into where you dont want it to go. Put some sewing machine oil (its very thin) on a piece of thin card and dab it in the tiny gap you can get with the focuser unscrewed as far as possible, screw it back in and keep screwing in out in out see if it gradually comes a bit further each time

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DRT

DRT

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Mark,

I have just had a thought that I cannot check right now so please don't do anything!

It is possible that the thread sticking out of the back of the focuser is an attachment ring that screws into both the OTA and the focuser, like the ring that attaches the ClickLock to a Baader Wedge. If that is the case it could be stuck at the OTA end or at the focuser end, or both!

Let me take mine apart again and come back to you so that you know exactly how this thing fits together. I will try to find time to do it tomorrow and report back.

Derek

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Highburymark

Highburymark

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On 11 February 2017 at 21:25, DRT said:

Mark,

I have just had a thought that I cannot check right now so please don't do anything!

It is possible that the thread sticking out of the back of the focuser is an attachment ring that screws into both the OTA and the focuser, like the ring that attaches the ClickLock to a Baader Wedge. If that is the case it could be stuck at the OTA end or at the focuser end, or both!

Let me take mine apart again and come back to you so that you know exactly how this thing fits together. I will try to find time to do it tomorrow and report back.

Derek

Thanks Derek - really appreciate the help - a light greasing hasn't solved anything.

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