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AT102 ED Focuser Slippage

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#1 Ouranos

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Posted 03 January 2013 - 11:01 PM

A few years ago I purchased the AT102ED with the Feather Touch Focuser upgrade. (I understand the focuser is/isn't Feather Touch) My question - how do I increase tension to prevent slippage with heavy eyepieces? There are two thumbscrews on the bottom of the focuser, but they still are not holding focus when tightened. The slippage only occurs with heavy eyepieces when I have the scope pointed toward zenith. The manual that came with the scope is not helpful on this point. Any advice is appreciated.

#2 WilRobinson

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Posted 03 January 2013 - 11:46 PM

My AT102 only has one thumb screw for tension on the focuser and it works very well, you might try contacting Astronomics.

#3 Ouranos

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Posted 08 January 2013 - 10:36 PM

Update - for those anxiously waiting. This past weekend I removed the focuser. The thumb screw used for tension was not doing anything. As I examined it - it became apparent it was screwing in all the way without any impact on the focuser. Sooooo, I went to the hardware store and purchased a similar screw - only longer. And, it worked. The longer screw put tension on the focuser. But, it did not look correct and I was concerned about damage the tip of the screw might do to the focuser. In the mean time, I examined the focuser - and shook it because I heard something rattling inside it. After placing the focuser back on the scope I tried the original thumb screw and - IT WORKED. It would only screw in half way and it tensioned up the focuser. Obviously, something was displaced in the focuser. I am not confident the problem is forever fixed. Has anyone had these focusers apart? How hard - to get back together. Any idea what I "fixed"?

#4 Eddgie

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Posted 09 January 2013 - 09:33 AM

First, I do not know what focuser you have, so this is a somewhat generic answer from someone that has taken apart about a dozen different kinds of focusers.

Next, I am confused.. Is it or is it not a Feathertouch focuser. These focuser are rack and pinion and are of extremely high quality, and don't (as far as I know) use two screws on the bottom. The Feathertouch focusers I have seen use a single large knob on the top, and if equipped with a brake, have a long, thin screw on the bottom.

Do you have perhaps a Crayford focuser?

Or is it the two speed drive that someone added?

A picture is worth a thousand words.

#5 Ouranos

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Posted 09 January 2013 - 10:12 AM

Here is why I say is/is not Feathertouch. My unit was shipped (as were many more) with this focuser. The seller said: "We state it is not an entire FT focuser, but a custom micro focuser for that particular unit. The bolts that hold the Micro to the body will adjust the tension and allow engagement. The knurled knob has a small black teflon peice that cradles the shaft. If you loosened the knob all the way then the saddle piece is now loose in your focuser. That is more then likely why the bolt will not give you drag on the focuser shaft". There were no efforts to deceive. But, there were some negative reactions from the CN community when an owner would write that the scope had a FT focuser. So, I always try to be clear that I realize the focuser is not entirely a FT. Hope that makes sense. I have no beef about the focuser except that I want to be sure the tensioner stays fixed. I will attempt to post some pics.

#6 Eddgie

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Posted 09 January 2013 - 10:39 AM

Well, a picture would help, but this is what I was going to suggest.

If it is a Crayford type unit (not a rack and pinion), the arrangement is usually similar. The smooth shaft is held against the flat ramp on the focuser tube by a nylon block with a groove in it.

The tension nut (typically) pushes against the bottom of the block to put more tension on the nylon block and increase the friction.

I was going to suggest that the nylon block had perhaps come away from the shaft and was not sitting square to it.

If this were the case, even just taking out the one screw and putting in another could have allowed it to come back into position, but then again, it may not be in the correct position even now.

But we can't know that without taking it apart to see. Usually there are some screws that hold the mirco-focuser in place and this will reveal all.

On the other hand, if it is working now, I would not fuss with it...






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