Focuser slip

[darthvader]

Hi folks, just about recovered from the 4 am eclipse marathon now..

anyway, i've noticed recently that my Dob 200P focuser is starting to slip when turned sometimes i.e. when i try to adjust focus, sometimes the focus assembly holding the eyepiece doesn't move unless i give it a helping hand... i sort of expected that with my 2" eyepiece as it's so heavy but it's happening with my other EPs too now.

Anyone know if it's possible to remedy the problem ? can i remove the focuser and adjust it ? 

Alternatively, I could buy a new, better focuser for my dob... and as xmas is approaching.....

thanks !

[triton1]

There is a central grub screw in the middle of the plate that holds the focusing wheels and bar in place.This controls the tension of the focuser.If you google "adjusting a crayford focuser" it,s the first hit,hope this helps.

[wookie1965]

Check out astro sheds crayford focuser modhttps://www.youtube.com/watch?v=ofOSAMlqZWw

[darthvader]

There is a central grub screw in the middle of the plate that holds the focusing wheels and bar in place.This controls the tension of the focuser.If you google "adjusting a crayford focuser" it,s the first hit,hope this helps.

thanks, i'll have a shufty tomorrow at it

[Charic]

...ditto the comments made by triton1.

I stripped mine out, to better  understand the internal workings, and there are modifications  on-line to improve the friction/stiction of that assembly.

It appears that the flattened section of the focuser tube only contacts the friction bar at the extreme edges, a fuller contact  is possible, however, I've not ground mine down yet with wet&dry, I just adjusted the tension screw, and all is well on my scope.

It does still slip a little when I stick my Nikon camera in the focuser, but that's expected,  I just  use the focuser lock!

[glowingturnip]

following this thread with interest as I too have a slipping focuser.

We had our first session (of many hopefully) in my kids' school observatory for this new school year. Great observing evening, and I saw Uranus and Neptune for the first time.

Something seems to have happened to the Moonlight CS Crayford focuser in the back of the SCT though, it was barely holding the weight of the hyperion eyepiece+diagonal without the focus lock being screwed in, and wouldn't rack inwards against gravity. 

It used to be ok, but I suspect it's been mis-handled by someone - at the start of the session, we couldn't figure out why the eyepiece wouldn't fit in properly, and the nosepiece of the eyepiece looked weird.  After some investigation, I found that the collar of the eyepiece was actually still in the focuser from some previous session, and that someone had forcibly unscrewed it to remove said eyepiece !  A rather nice Baader hyperion aspheric one too - argh !  I suspect the drawtube may have got twisted round inside too which is why the mechanism isn't holding.

[darthvader]

All sorted now folks, thanks for the tips. I adjusted the centre screw in the panel (see picture) with an allen key and all is hunky dory again 

[darthvader]

forgot the picture .... !

[darthvader]

on the down side that means i don't need to buy a new flash focuser 

I'll have to find something else to 'waste' my money on 

[niallk]

Glad you got it sorted. In case useful to anyone - there are pics here of a disembled SW focusser to see what's inside, and instructions on how to adjust it.

http://www.teleskop-express.de/shop/product_info.php/info/p2625_1-10-micro-transmission-for-retrofitment-of-Crayford-focusers.html

[darthvader]

Glad you got it sorted. In case useful to anyone - there are pics here of a disembled SW focusser to see what's inside, and instructions on how to adjust it.

http://www.teleskop-express.de/shop/product_info.php/info/p2625_1-10-micro-transmission-for-retrofitment-of-Crayford-focusers.html

that's all German to me !  does that mean my focuser passed all the factory checks ok but will emit harmful gases when in use.....     Vorsprung durch Technik 

[niallk]

Ha ha - click on the little flag near upper right of webpage to make it English... as it was when I copied the link.

As an aside, this little £50 upgrade is well worth it - might even be useful for smoothness if you find your focusser stiffer after tightening it up to cope with heavy loading - the 1:10 gearing will still feel nice and light, and precise.

All the best