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pevsfreedom

What's wrong with my focuser?

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I just noticed yesterday (haven't used the scope in a bit) that my focuser is essentially "messed up". It's a crayford 2" focuser (basically this) and the knobs are clunky/grindy while they used to be super smooth. It actually almost takes force to move them and I can HEAR them scratching/grinding.. do they require oil/greasing of any sort? The only thing I can think of happening is I hit it when I tried to shove it in my car last week though I didn't notice anything... it looks fine. This is all besides the 'setting screws' of course - no matter what I do it still grinds - and this is WITHOUT any eyepieces. 

Edited by pevsfreedom

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Have you made sure the locking screw for the focuser is undone completely and also is the shaft straight between the knobs you did say you knocked it

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Could you have sand in your focuser?

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Sounds like the shaft may be bent. If you can establish the diameter accurately they can be found on ebay cheap enough. You will have to trim to length of course.

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Could also be a damaged roller bearing. Same applies.

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Have you made sure the locking screw for the focuser is undone completely and also is the shaft straight between the knobs you did say you knocked it

Well I might have knocked it - I can't say if I did or not - it's the only thing I can think of. Locking screw is undone and tensioner doesn't affect it. 

Everything looks straight as far as I can tell. 

Sounds like the shaft may be bent. If you can establish the diameter accurately they can be found on ebay cheap enough. You will have to trim to length of course.

Hmm I wouldn't even know where to start with this! :(

Could also be a damaged roller bearing. Same applies.

Is there a way to take it apart and check? 

Could you have sand in your focuser?

There could be something though I've moved it around a lot and it hasn't stopped.. Hope I didn't just "Bang" it while shoving it into my trunk. 
Edited by pevsfreedom

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Sometimes roughness and noise can be adjusted out. Didn't suggest this as you seemed to have tried it. Adjustments would be worth it. A tiny part turn makes a big difference.

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Sometimes roughness and noise can be adjusted out. Didn't suggest this as you seemed to have tried it. Adjustments would be worth it. A tiny part turn makes a big difference.

I'm assuming that's in the allen key slots on the focuser? I tried a bit yesterday but it didn't move - might try harder today. 

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Could be but given what you say, I would take off the four screws holding on the bottom plate and see if anything is amiss. Upload pics if you like.

Ironically the image you linked to shows the problem with some of these focuses. Look carefully at the flat on the draw tube and you can see that the shoulder is wearing indicating the flat is not quite flat

There are some decent you tube vids showing how to grind a proper flat. It's a simple diy job.

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Hmm I have some homework if that's the case. I'll take it apart in a bit. I suppose the only thing that could have happened is I bumped it hard - I don't remember doing it but who knows. I don't think something like that would just happen from gravity from sitting still!  :grin:

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When I sold my 12" dob - the chap I sold it to bumped the focuser on a door jam and it damaged one of the roller bearings inside resulting in exactly the same scrunching noises and resistance you describe above.

The good news is that the roller bearings can be replaced for peanuts (he got a bag of half a dozen for under a tenner). You just need to strip it down to check them - change the damaged bit(s) - and reassemble. I'd also recommend looking up Dions Youtube presentation on servicing the Crayford at the same time while you have it apart. Hth :)

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I got it fixed! I e-mailed manufacturer and he said to loosen the fine focus knob and pull it a hair back from the coarse knobs and it fixed it - the bump must have pushed them too close together. 

Edited by pevsfreedom
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