Skywatcher Dual Speed Crayford

[SteveA]

Since I bought my Skywatcher CF Quattro I had never been very happy with the smoothness of the focuser, (2" dual,speed Crayford) it always felt slightly rough. However I only tend to use the fine focus knob on my focuser these days as the camera really only needs the fine focus and I was able to ignore this.

Having just bought the Autofocuser I set out to install this but discovered that the rough action when using the coarse focus had now become decidedly worse. Whilst attached to the OTA there was an audible crunching noise when using the coarse focus and it almost sounded like the focuser was full of grit ! Obviously it was time to investigate the inside of the focuser and see what was going on.

This focuser has two knurled knobs for locking the tube in place. One of these applies force to the spindle from the underside of the focuser, whilst the top one acts directly on the top of the tube. These were removed along with the four Alan bolts on the underside of the spindle assembly, allowing the assembly to come free from the focuser. Immediately signs of rust were were visible on the spindle.

I hadn't really appreciated the fact that this focuser actually incorporates a flat rail which is attached to the underside of the focus tube, the spindle acts on the flat surface of this rail, quite unlike the examples I've seen on various sites where the spindle acts directly on a flat strip on the tube.

The next job was to remove the focuser tube. Simply removing the proud Alan bolt from the rail at the back end of the tube, allows the tube to slide free.

And there it was RUST...and Lots of it. The rail that the spindle acts on has two machined groves on either side and these were full of it. I could see that rail slides through some sort of gizmo inside the focuser assembly and whatever this was was held in place by four screws that became visible when removing the spindle assembly, I removed these and discovered a rust clogged and very scruffy looking linear ball slide with the designation LWL 9A.

Clearly some cleaning was needed so I took to the rail with some fine wet and dry and removed as much of the rust as I could. There was rust and metal swarf tangled up with the ball bearings in the slide, so I did my best to remove as much of this as possible without releasing the ball bearings. A few did drop out but I managed to re-insert these fairly easily.

There was absolutely no kind of lubrication anywhere! I realise that that the Crayford relies on friction, so clearly the upper surface of the rail needs to be free of grease, but the slide and the machined grove seemed to be crying out for some. I applied a small amount of lithium grease to the bearings and the rail groove.

I was also surprised to find that the force is applied to the spindle not through any nice Teflon coated surface but just a concave metal surface!

Once re-assembled the focus action is much improved. I can't ever see it being silky smooth, but certainly a vast improvement.

My general impression of this focuser is not good. Clearly it incorporates cheap components and the lack of lubrication only enhances the formation of rust, this definitely not a quality piece of equipment! If I can I am going to try and source a replacement ball slide, hopefully a slightly better quality one. Unfortunately getting hold of one of these looks tricky..anyone out there got any idea where I could get one from?

[HD-AP]

Hi

Revalation focussers are a good upgrade ,availiable from telescope house .

[russ.will]

Nice examination of the issues with this focuser, which has some nice features, but as per usual lacks something in the quality materials department. A focuser shaft, that bears on metal NOT made from stainless steel. Really?

I suspect you would be lucky to source replacement component parts, with the exception of the ball races, which would be easy enough through a local factor, or off the interweb.

It may, as per usual, be easier to cut your losses and just get a decent focuser. As an imager, it was bound to happen sooner or later.

Russell

[SteveA]

I guess you are both right and I will eventually end up replacing the focuser. Unfortunately I've already spent this years permitted allowance on astro related stuff, so unless I can sneak this past SWMBO, I'm stuck with it for the time being. And I've just forked out for the SW Autofocuser, so I'm really not keen to dump this just yet.

I'm hoping the service I've just done on the focuser will keep it going for a while longer and being pragmatic despite the rust and stuff the thing has been working. Looking on the bright side..there's not much chance of focuser slip with a rusty focuser, right?

[Tommohawk]

Hi! I know this is an old thread, but I have similar problems plus some of the ball bearings are missing. Don't suppose you know the diameter? I dont have a micrometer. 

[iapa]

On ‎11‎/‎05‎/‎2015 at 08:47, SteveA said:

I guess you are both right and I will eventually end up replacing the focuser. Unfortunately I've already spent this years permitted allowance on astro related stuff, so unless I can sneak this past SWMBO, I'm stuck with it for the time being. And I've just forked out for the SW Autofocuser, so I'm really not keen to dump this just yet.

I'm hoping the service I've just done on the focuser will keep it going for a while longer and being pragmatic despite the rust and stuff the thing has been working. Looking on the bright side..there's not much chance of focuser slip with a rusty focuser, right?

Let us know how you get on with the SW autofocuser plse.

Looking for hints on modifying the motor bracket to fit Quattro focuser.

 

 

[SteveA]

1 hour ago, iapa said:

Let us know how you get on with the SW autofocuser plse.

Looking for hints on modifying the motor bracket to fit Quattro focuser.

 

 

Well...this was all some while ago..but!

I did manage to attach the autofocuser, but it involved a hacksaw and a vice and tbh it was a bit of a bodge. However I was so dissatisfied with the the actual focuser assembly that I did eventually swap it out for a Baader Diamond SteelTrack. I couldn't afford the SteelDrive at the time but am currently waiting for this to be available again..apparently Baader withdrew the original SteelTrack for the Diamond range and are redesigning this. So...as it stands I still haven't got an autofocuser 

Steve

[iapa]

5 hours ago, SteveA said:

Well...this was all some while ago..but!

I did manage to attach the autofocuser, but it involved a hacksaw and a vice and tbh it was a bit of a bodge. However I was so dissatisfied with the the actual focuser assembly that I did eventually swap it out for a Baader Diamond SteelTrack. I couldn't afford the SteelDrive at the time but am currently waiting for this to be available again..apparently Baader withdrew the original SteelTrack for the Diamond range and are redesigning this. So...as it stands I still haven't got an autofocuser 

Steve

I've used the SQ autofocusers on other OTA, but like yourself, found needed some 'modification' for th equator.

Not doing much this weekend, so, will get the old deme et. all. out  

[Tommohawk]

Hi - sorry my fault for raising an old thread but the detail on the focuser strip down was so good and I was desperate to figure out the bearing size!

Turns out the bearings are 2mm so I got some and replaced these and cleaned the focuser. There was no visible rust on the spindle or elsewhere but lots of bits of something. Despite a good wash in petrol and new grease it's still a bit crunchy, though by the time the top tensioner and the focuser tension are set, this seems indiscernible. I think the main problem may be an irregular bearing slide.

Anyhow the main reason I stripped it is because initially it had quite a lot of play and this is now eliminated so I'm happy for now though I agree with otheres that the design/materials are a bit cheap.

That said, for the price the Quattro is still really good value, so I'm not complaining! All I need is some clear sky to check it out and there's no sign of that!

Re the SW autofocuser, for starters I don't know why this is called auto focuser - this implies it can find focus automatically - would be better referred to as a motor focuser. Pedantic? Maybe!

Anyhow, by chance my Quattro, bought used, was fitted with the SW motor focuser. The way the previous owner did it was to only use two of the mounting screws, and also he spaced the motor away from the bracket. Fitting with 2 screws obviously not ideally but this doesn't seem to compromise things. Main issue for me is I prefer to use manual focus for general set up - finding focus with new optical train etc - and just use motor for fine focus esp on high mag planetary stuff.... but there's no way to disengage. Heres a pic of the motor only - he used the 2 holes which have been countersunk.

BTW if doing this I advise loosening the top tensioner first, tightening the 4 focuser knob assy plate screws fully, and then retensioning the top plate. ON mine the top was over tensioned, so the focuser plate could not be fully tightened - hope that makes sense! Then tension the 2 screws on the underside so the focuser has the desired level of friction.

 

[Tommohawk]

BTW I do like the idea of having 2 lock screws, both top and bottom. This helps to prevent the lock screw pushing the opposing tensioner out of adjustment, and also helps ensure the focuser tube remains orthogonal.

+1 for the design!