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is it possible to adjust a standard crayford focusser?


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Hi all,

I have a skyliner 250px dob with the standard crayford focuser and i'm wondering if it's possible to adjust it to make the travel smoother and able to move with more weight. I had been considering the micro focuser upgrade for my crayford. Accessories @ Modern Astronomy

But i'm not sure if this would solve the problem.

Is the skywatcher dual crayford focuser better able to handle the weight?

Brian

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How much weight are we talking about ? Have you considered a Moonlite Focuser upgrade ? I know it might be outta of your budget, but they can carry an excess of 5kg or higher.

Nadeem.

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Brian, not sure if this is going to help but I've taken both my crayfords apart.

The latest was a cheaper GSO/ WO clone sct type which had a similar problem. It would track out so far but then struggle etc.. and when using it you could "feel' it wasn't too smooth.

Basically I took the focuser hand wheels off , took off the pressure plate, removed the rod and pulled out the tube.

Checked the bearings and found one was very stiff and another wasn't turning all the time -these could be easily regrease with a spray teflon/silicon grease and I loosened the screws just a wincy bit ! As for the tube - the flat bit, well run your fingers over it and feel for lumps/bumps etc -it ought be absolutely silky smooth and flat. There are a variety of ways of achieving this using very fine W&D papers/carborundum, just be gentle ! alittle bit at a time . When your happy that it's as smooth & flat as you can get, rub some good quality beeswax onto it and then buff it up !!

NB If you do this ensure you use a hard flat block former to prevent any uneven abrasion over the surface. It needs to be as flat as poss to be effective.

Check the rod for kinks /signs of rust/ deposits on the surface. Some very fine wire wool will clean it . If it's kinked replace it with St St rod (generally 4mm, available from model stores).

There's a brass/steel bush that the rod runs thru and holds the rod in place between the tube and the crayford body, again just check that this isn't fouling. Again I used some fine paper to put a n almost mirror finish on the inward facing surface- then put it all back together and hopefully that shoul;d do the trick.

They're pretty simple mechanical objects-probably just needs a bit of fettlin' :)

HTH

Edited by beamish
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I love this site!!!!

Thanks Astro Baby thats what I was after.

Karlo by taking the focuser apart to explore the mechanics will I mess up the alignment? I see it has some plastic down the back side of the tube. I'm guessing this will fall out and so need to be replaced to get it aligned again. Is that a hard task?

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Well the screw on the base will tighten it but the feel will go when you put lighter EPs in it.

Ritchie - I'd kind of agree a Moonlite is the best but I am trying to spare Brians credit card.

All I'd say is resist the temptation to play witha Moonlite because after that noting ever feels as good :)

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I love this site!!!!

Thanks Astro Baby thats what I was after.

Karlo by taking the focuser apart to explore the mechanics will I mess up the alignment? I see it has some plastic down the back side of the tube. I'm guessing this will fall out and so need to be replaced to get it aligned again. Is that a hard task?

No ! 'cos you leave the body exactly where it is attached to the scope, it just all the bits can be removed for closer inspection :D Even the lickle bearings can be removed without moving the position of the body at all !

Just make sure there's no risk of anything dropping thru onto the 2ndry :)

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This generic info Brian NOT specific to your particular crayford- but they are all just variations on a simple design/process. You did ask the original Q :) If you feel confident enough try it .

Ooh the tensioner screw would be the 1st approach prior to the dismantling tho !!

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thanks guys, just dismantled it and it was easier than i thought. There was 2 polished lines down the outside of the flat surface with the rest powder coated shiney stuff on the rest.

I cleaned the bar and put it back together tightening the four screws slowly while moving focuser in and listening for change in sound.

Long and short of it when i put the uwan 28 in it lifted it no problem. Sorted.

Put in lazer and think the dot moves a couple of mm. might look at this sometime.

Thanks again.

Brian

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Karlo,

the grease you mention. is that like the lithum grease people recommend for regreasing mounts with. Where did you get it? do you use much of it or is a light greasing.

No it's not the lithium grease Brian, it was a spray can of light silicon grease-I think I got it from a bike shop :)

The movement you describe - is this when you tighten the lock screw on the pressure plate to engage the rod/roller mechanism bit of the focuser ?? If so that's pretty much the norm, tho if it's really bad, again there are measures to improve such as adding (gluing) an ally shim down the tube where the lines from the roller bearings show up.

Merlin 66 put me onto a good tip CocaCola cans !! (it's all they're good for !!) EASY TO CUT TOO !!:D

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Karlo as I was tightening the 4 ataching screws for the plate holding the focuser rod on I was trying to ensure it went on level and was tightening and loosening screws until there was no sound when racking the focuser in and out. I was conscious of the possiblity of over tightening the plate and possibly bending the rod. Is that possible? I ended up getting the desired tension for focusing just by tightening these holding screws rather than the focusing tensioning screw.

The movement I mentioned was when I put the lazer into the focuser and racked the focuser in and out. It is only a couple of mm movement in a diagonal direction. Is that something that can be removed by the colimation screws or as i have had the focuser off to flock the tube, might it just be a matter of adjusting the fixing screws that attach the focuser to tube?

Thanks for all the help.

Brian

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It'd be very difficult to bend the rod Brian, but I wouldn't go so far as to say impossible !

As for the movement you spoke of- I doubt that is something that could be removed. Imperfections in the roundness of the tube I guess.

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fair enough it's not a big movement. I'll maybe have a bit of a play to work out where it's coming from.

I just got a 2nd hand howie glatter laser today and am impressed with it used along side my chershire and barlow thing. I'm dying to get out and use it in anger now under dark night conditions.

Thanks

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