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Refractor Focuser Slipping

Dave-Ryan

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Dave-Ryan

Dave-Ryan

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I have an unbranded 80mm refractor that is almost identical to the Skywatcher Equinox 80 APO.

My problem is the focuser keeps slipping when I have a Meade DSI pro III attached to it and the locking nut as tight as I can get it. I have tried using a diagonal and an extension tube (the extension tube seems to be the worse of the two).

Is there anything I can do to avoid the slipping or is this telescope going to be only any good for visual use?

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Euan

Euan

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That's strange that it still moves when it's locked off. I have a Moonlite on mine now, but even with the old one it would usually be rock solid

Have you tried the two little hex screws next to the locking knob? If I remember right this pushes the focusing part tighter against the tube

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Bizibilder

Bizibilder

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Have you stripped the thread on the locking screw? It may "do up" but then promptly ondo when under load.

OR Is there a "pad" under the locking screw (that is there to prevent the screw damaging the tube) it may only be a tiny bit of metal or Nylon or similar. If there should be it may have fallen out!

If you take the tube out can you screw the screw in far enough that you can feel it protruding into the tube? ie is is able to reach and therefore lock the tube.

Hope this helps.

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Dave-Ryan

Dave-Ryan

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The scope hasn't had very much use, although I've had it for over two years, and after inspection the threads seem fine and there is a nylon pad under the locking screw.

The telescope is in almost new condition, due to lack of use, so is very frustrating.

I was out on Monday night and found every time I had the DSI pro III focused on my laptop it would lose focus within 30 seconds. I found this was due to the focuser slipping with the weight of the DSI. I replaced the extension tube I was using with the DSI for a diagonal and this seemed to give me a little more time but it would still slip eventually.

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Bizibilder

Bizibilder

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Ah! The nylon pad under the locking screw!! Maybe this is the problem - sometimes these stick in the thread and when you tighten the screw the pad is "wedged" - you feel the thing is tight but it is in fact not even in contact with the tube! I would investigate in this direction first and see if it solvs the puzzle.

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johninderby

johninderby

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Good, now I know which one it is. I've got the identical one in front of me right now.

Does the end of the locking screw have it's nylon tip? If not then that's the cause of your problem. But assuming it is then it's best to tackle the setup of your focuser from the beginning to eliminate other potential causes.

On each side of the centre of the focuser there is a set of three hex screws, one black and two silver. These are a push-pull arrangement. If you slacken off the silver ones then you'll be able to tighten the black one and vice-versa. These set the closeness of the focuser knob shaft to the bottom of the drawtube.

If you back off the tension screw (and the locking screw of course) does the drawtube slide in and out easily by hand and the focuser knobs don't move the drawtube at all? If the drawtube sticks and doesn't slide easily by hand then the focuser knob shaft is set too tight against the drawtube. Conversely if the drawtube is loose and rattles about then the shaft isn't set close enough. The idea is to have the drawtube slide easily but not be loose. That's where you use the hex screws to get this clearance right.

Once that's sorted out adjust the tension screw to get the resitance right. Hopefully that will sort it out and the locking screw will now work properly.

One last thought. Has the drawtube been polished at all. If any polish or grease gets on the bottom surface of the drawtube then the locking screw won't work.

John

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Dave-Ryan

Dave-Ryan

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When I unlock the locking screw the drawtube will slide out easily by hand and the knobs do not move. The drawtube does not feel loose nor does it rattle.

Is the tension screw the black one in the centre?

Oh! the drawtube has not been polished.

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johninderby

johninderby

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It's sounding like it is just the locking screw. What condition is the nylon tip on the screw in? It should be flat with no chips. You could try sanding the tip lightly to make sure it's flat which would also remove any contamination from the tip.

John

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Dave-Ryan

Dave-Ryan

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It's in perfect condition John.

Although I have had the OTA for over two years it has had very little use.

I'm wondering if it is possible to paint or stick something to the flat part of the drawtube to give the nylon pad a little more resistance from slipping.

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johninderby

johninderby

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[quote=Dave-Ryan;1518141

I'm wondering if it is possible to paint or stick something to the flat part of the drawtube to give the nylon pad a little more resistance from slipping.

I've never found that necessary. Try cleaning the bottom of the drawtube with a degreaser or other suitable cleaner. I've found that if you remove the focuser from the OTA you can then gain complete access to the bottom of the drawtube for cleaning. I'd then lightly sand the nylon tip of the locking screw to make sure that it's grease free as well.

John

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Dave-Ryan

Dave-Ryan

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Thanks John, and everyone else who answered my question.

I'll give this a try, it doesn't feel like it would take much for this to work. I was looking at the Moonlite euan mentioned but the cost of that is almost as much as the OTA cost me so lets hope your suggestions work.

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johninderby

johninderby

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John thanks for the info on setting up the focuser.. what does the center allen screw do?

I had no joy getting a replacement for the my damaged Equinoxe-66 .. TS didnt have any B grade parts... so i am going to try and "fettle" it...

Peter...

The centre screw is the tension adjustment. I think TS has the complete replacement focuser but at about £100.00 it's not a cheap solution !!1

John

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johninderby

johninderby

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John

I never touched the tension screw because I wasn't sure which one it was. Do you recommend I adjust this screw?

Yes, you normally need to adjust the screw to get the focuser to work correctly. Loosen the screw until the drawtube slips a bit and then tighten it a bit at at time until the drawtube doesn't slip when you push lightly on the drawtube. You want just enough tension so that the diagonal and eyepiece don't move under their own weight. Too much tension and the focuser can be stiff to work. You just have to play around with it a bit until you get the balance right.

John

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