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Rogering1

What's wrong with a Crayford Focusers?

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The concave surface issue has been there from the start with those Skywatcher crayfords. What baffles me is why a company like Synta (who manufacture Skywatcher) can't machine a short, flat surface on the bottom of a tube :icon_confused:

Having a really flat surface there seems to me to be a critical part of the crayford design - if you can't achieve that then perhaps its best not to try and make the things !

Having said that, the Orion Optics crayford suffers from the same issue ...... :rolleyes2:

Criminal isn't it really. You would have thought companies would have learnt how to make a flat surface by now.

Also, having just metal on metal is surely bound to allow slippage also??

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Second day after giving my Crayford a good going over and working to what it was made for, still carrying the weight of the camera at all angles, I for one am happy with it. I still see I have not got a reply to my question on recommending a new focuser, thanks for that, glad I was not in a hurry :).

Jim

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I have the WO ZS70 2012 with dual speed rack and pinion focuser........i was experiencing an amount of lateral movement on this and it looked like it was going back to the supplier, i was reluctant to give up on it, and spent a little time looking for where the movement was coming from, turned out to be the lock screw that allows the focuser body to rotate 360 degree`s :shocked: this needs locking a little tighter than expected, if this is not done then the housing "rocks" a little side to side.

Having got past this little hurdle, its a very good focuser, no slippage at all, not as smooth as a crayford but not a million miles of

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I still see I have not got a reply to my question on recommending a new focuser, thanks for that, glad I was not in a hurry :).

I replaced my focuser on my Skywatcher with a Moonlite and I found the difference massive. I then bought a decent scope with a standard R&P focuser. It is miles better than the Moonlite, so much so that I may replace the Moonlite with a Feathertouch. So in my opinion, having a Moonlite on one scope and a R&P on the other, the Moonlite is no where near as good. I'd not bother with another Moonlite and would go for a Feathertouch from the onset.

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Thanks Sara, I am not ready to upgrade my OTA just yet so I will be doing with what I have. It has irked me that a week or so ago a thread about "Google it" as a reply to some questions was not what was required by people and I have asked a question withouty a reply, funnily enough I did "Google it". I have solved my own problem without an answer from here so am happy in myself, thanks again :).

Jim

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Surely Monique doesn't need all those pairs of...

Olly

Mittens?

Russell

Sent from my iPad using Tapatalk HD using chubby fingers. Sorry.

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I replaced my focuser on my Skywatcher with a Moonlite and I found the difference massive. I then bought a decent scope with a standard R&P focuser. It is miles better than the Moonlite, so much so that I may replace the Moonlite with a Feathertouch. So in my opinion, having a Moonlite on one scope and a R&P on the other, the Moonlite is no where near as good. I'd not bother with another Moonlite and would go for a Feathertouch from the onset.

I'm in more or less the same place now. I've put an older Moonlite dual speed on my ED120 which was an noticeable improvement over the William Optics that was on there before and that in turn was a step up from the Skywatcher crayford that was supplied with the scope. My decade old Vixen ED102SS has the original well engineered R&P focuser but when I first got the scope a number of people suggested that I should upgrade the focuser to a crayford as an early modification. Well I'm glad I didn't because the Vixen R&P is one of the best focusers I've ever used, now having the benefit of trying quite a lot of others.

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I have been building an ultra low profile '~Crayford-style' focuser for imaging only this weekend. Leverage was my main concern with a DSLR. So I did some levering as I assembled. Without resorting to some CAD analysis software, I have to say that the basic design is for smooth movement without precision engineering skills, not holding the drawtube perpendicular (it has a spring in it - surely a big clue!). Or for pulling heavy loads against gravity. A three-legged stool doesn't wobble and can be quickly made by the milkmaids - but is less stable. An engineer care to analyse and confirm this? After adding a fifth bearing things improved.

An internet search reveals some monster engineering to overcome the inherent lack of stiffness. And even a (different and revealing) 5th bearing design! All the expense and extra bulk of metal and big bearings thrown at the problem is evident in the 'good' products on the market. To push a shaft onto a tube with enough force to grip needs three ball bearings set up behind it, not a (squashy) 'virgin teflon pad'. So it can't flex away, and allow the drawtube to flex.

So the adverts for red anodised CNC perfection should really say - 'we've taken the basic design from an amateur for a low-precision focuser and added as much (or little) metal as possible to make it work, made it look really high-tech, finished it in shiny red or green, and even then some people are disappointed'

Mine works in the sense that the drawtube moves smoothly over the intended 6mm range, it is probably extremely rigid compared to most commercial units. It cost 45p for some nuts and bolts I didn't have the right size. There isn't a lot of metal in it and I used hand-tools and a pillar drill.

My Crayford is not as rigid as the set-up I had used before, where all the parts were machined and bolted together and fine-focus involved tweaking a sliding intereference fit between two concentric tubes and locking them together with screws.

The Crayford is the wrong engineering solution for heavy imaging trains.

Is it a marketing ploy for one commercial unit to put a top secret 'warranty void if removed' sticker on its' product? - at the same time quoting on its' website the generosity of Wall to donate his wonderful idea!

Please can someone else like Wall come up with a new design? Try throwing away all those catalogues of Crayford focusers and get busy in the shed.

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Have to say that since I stripped and done some maintenance on my Crayford it has preformed perfect, even added some extra weight. Not once has it given me a problem, whereas before the strip I would hold my hands under it awaiting a crash as it slipped, have now forgotten all about that and happliy stand back when slewing, happy days :)

Jim

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