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slippy sloppy focussor !


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Greetings fellow gazers ! I'm positive this ain't a new thread but i thought i'd post it anyway ! I have a skywatcher r+p type focussor and boy is it a tetchey git

!:D Spent a good while finding M31 the other night and every time i had the beast nearly in focus Bang ! the dashed thing would slip:angry4: eventually i hope to replace the codpiece with a real crayford type (ie-moonlite...yum !) but at the moment being financially challenged, to say the least i have to make do........Question is.. does anybody have a hard and fast method of reducing the slip slop action of these beasts ? Because I'm desperate !:cussing:tried various things to no avail ! pls help me brothers and sisters !? ta much Iain.

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There are 2 very small hex screws either side of the large black knob that will adjust the tension in the focusser - they are worth experimenting with. The 4 screws underneath the focusser, that hold a plate which in turn keeps the pinion gear in place, are worth playing with as well. With a little patience and some quality lubricant you can get these R&P focusers performing pretty well.

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Greetings fellow gazers ! I'm positive this ain't a new thread but i thought i'd post it anyway ! I have a skywatcher r+p type focussor and boy is it a tetchey git

!:mad: Spent a good while finding M31 the other night and every time i had the beast nearly in focus Bang ! the dashed thing would slip:angry4: eventually i hope to replace the codpiece with a real crayford type (ie-moonlite...yum !) but at the moment being financially challenged, to say the least i have to make do........Question is.. does anybody have a hard and fast method of reducing the slip slop action of these beasts ? Because I'm desperate !:cussing:tried various things to no avail ! pls help me brothers and sisters !? ta much Iain.

excuse my ignorance :),what are the main differences between a

crayford and r & p is the term "crayford" a type or make? i am looking at a crayford from astronomica uk :icon_scratch: is this just a generic term for a type of focuser and more importantly does the term guarantee quality :)

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what are the main differences between a

crayford and r & p is the term "crayford" a type or make?

"Crayford" originates in a designed developed at a local astronomical club in the 1960s. Nobody makes a true Crayford, the true Crayford type allows you to change the whole focuser tube ... at the time this was convenient because "standard" eyepieces were threaded rather than push in.

A rack and pinion focuser uses a rack and pinion. Modern pseudo-Crayford focusers use friction between a shaft and a flat plate to achieve the same effect (the original just used the side of the focuser tube ... no flat plate ... but did have a rubber or plastic friction tube fitted to the shaft).

R+P focusers - done well by e.g. Moonlite - work exquisitely; there is neither slop nor slip and the movement is very finely controllable. But, made badly or allowed to get dirty (congealed grease), they can be less than pleasant to use. Modern pseudo-Crayfords have a tendency to slip under load and/or have a stiff action ... the best that can be said for them is that they're cheaper to make than a good R+P and can work well enough once you have the tension set right. Until the friction shaft or plate gets dirty, then you have to dismantle, clean up & spend a happy hour or two getting the tension to the point where it grips well enough for you heavier eyepieces / camera not to make it slip, yet is still free enough to allow for precision focusing.

As you'll have gathered, I'm not that fond of modern commercial Crayfords. Some of the better ones work well enough but they ain't cheap ... and top end scopes by e.g. Takahashi don't use them.

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The problem lies with the draw tube, if you look underneath where the flat part is, you will notice there will be either one side edge of it or both side edges of it quite shiney, this is where the problem lies.

The tube hasnt been cast or machined perfectly flat, so the roller (not sure of its techinical name!) is pressing on either one side or both, instead of running perfectly across the whole width of the flat part of the tube.

To remedy it, you'll need to dismantle the focuser and remove the draw tube, then after wrapping a cloth around the draw tube, place it snugly in a vise and then using an Oil stone..CAREFULLY flatten the the flat part of the draw tube so its perfectly flat.

Its not a hard job to either dismantle focuser, or flatten the tube, but it must be done carefully.

When i did my Skywatcher 80ed pro tube, i flattened it a very small amount and retried it, it made the turning of the focuser nobs quite stiff, but instead of removing it and doing a bit more, i left it as it was as it was perfect for me because i only use my 80ed for astrophotography, which means once ive achieved focus, there is not slipping anymore due to the weight of my Canon 350d.

There was a website showing how to remove the focuser etc, i'll see if i can find it and post the link for you Iain.

Edited by Mick UK
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Lovely solution for the Skywatcher crayford (or pseudo crayford) Mick but Iain has a rack and pinion focuser - he will have a rack on the bottom if his draw tube rather than the flat area :)

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For your R&P there is a simple mod to do by adding three strips of PTFE tape which I found vastly improved the slop and sag in the focuser. Simply put them at 120 degree spacing along the axis of the tube, makes it slide much better in its bore.

PM me and I'll put some in the post to you, I've got about 100m left from when I did it!!!!!

Also, I find that the Skywatcher Auto (really motorised) focuser helps a lot with twitchyness and tube shake compared to turning the knobs by hand!

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Iain. I second what Jahmanson posted about the two small socket hex srews either side of the locking knob being adjusted to cure the slop. They are iniscule and easily overlooked, you will need a very small Allen key.

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"Lovely solution for the Skywatcher crayford (or pseudo crayford) Mick but Iain has a rack and pinion focuser - he will have a rack on the bottom if his draw tube rather than the flat are"

Ha!..so he does John!:icon_scratch:...i should stop been so eager to help people and learn to read all thier posts thoroughly before i dive in!:)

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"Lovely solution for the Skywatcher crayford (or pseudo crayford) Mick but Iain has a rack and pinion focuser - he will have a rack on the bottom if his draw tube rather than the flat are"

Ha!..so he does John!:mad:...i should stop been so eager to help people and learn to read all thier posts thoroughly before i dive in!:)

For those that have a Skywatcher crayford, your tip is well worth following - the "flat" part of the focusser tube on the examples I've owned, was distincly concave :icon_scratch:

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One other method i used to use to stop the slipping before i dismantled it and flattened it, was toput an elastic band around one of the pinch knobs holding the diagonal onto the draw tube and the other end of the elastic band around the focuser wheel.

You'll soon work out how tight the band needs to be (not very) to stop the tube slipping out over and also to help you focus in over as well.....thats if your R & P works the same way as the Crayford focuser!... :):icon_scratch:...you wont find a much cheaper solution than this either:p

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back in my musical days there was nothing that "gaffa" tape could not fix ! broken limbs, marriages you name it even the singers voice ! spose it's a bit like that with PlumbersTapeForEverything he! he!

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