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Cave Astrola RA Clutch

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#1 2manyscopes

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Posted 02 November 2006 - 10:45 PM

Hi all,
I have several Cave Astrola mounts with original RA drives and clutches. Two of them I have never used. The most recent mount carries a 6" f/15 refractor and I am using it every chance I get. The problem is that the motion in RA is too loose. When I adjust the three screws on the clutch, the feel becomes strained and jumpy. The tighter I go the worse it gets. I have adjusted it so that it still moves free and smooth but is as tight as possible without introducing the strain and jummpiness. Problem is, it's still too loose.

On this mount the clutch has grease between the aluminum plates. My other two mounts do not have this grease in the clutch so I am wondering if the grease should be in there?

Thanks,
Bill

#2 tybee

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Posted 03 November 2006 - 05:45 AM

You don't want grease on clutch plates. It'll make the clutch slip which is probably the cause of the jumpiness.

#3 Rcade

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Posted 04 November 2006 - 06:41 PM

I have an 8" Cave Astrolla and it does NOT have any grease on the plates. I think tybee is right. My plates are not shiny either. This makes for a slightly rough surface that grips enough to make the drive track but can slip if need be.

Another area to look at is the springs themselves. I did replace the original springs with newer stiffer springs and stainless screws. The action is much better. If the old springs were left under tension for a long time they may not be strong enough to lock in the drive.

#4 2manyscopes

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Posted 09 November 2006 - 08:59 PM

You don't want grease on clutch plates. It'll make the clutch slip which is probably the cause of the jumpiness.



Thanks Tybee. That is what I thought.
Bill

#5 2manyscopes

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Posted 09 November 2006 - 09:16 PM

I have an 8" Cave Astrolla and it does NOT have any grease on the plates. I think tybee is right.

Another area to look at is the springs themselves. I did replace the original springs with newer stiffer springs and stainless screws. The action is much better. If the old springs were left under tension for a long time they may not be strong enough to lock in the drive.


Thanks for the reply Rob. The next dry day I get I'll take the clutch apart and clean it up.

Springs huh? That is another odd thing about this mount.....there are no springs. My other two Cave Astrola mounts have springs and no grease. Do you have any idea how stiff the springs need to be?

Thanks,
Bill

#6 Rcade

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Posted 09 November 2006 - 09:34 PM

I don't really have a way to measure how stiff the springs are. I took my old springs which the ends could easily be compressed and got springs about 1/4" longer and of a heavier gauge wire. They made a big difference in how smooth the drive works. I think I paid about $3.50 for the springs. They are about 1-1/4" long and 5/16-3/8" in diameter(not exact). I have never seen a Cave mount without the spring type setup. I wonder if sometime in the past the springs broke and the repair was made without springs for some reason. If you tighten the clutch up with no clearance then the grease would help let it slip. If you need me to I copuld disassemble my clutch and measure the springs for you???

#7 tybee

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Posted 10 November 2006 - 06:50 PM

Thanks for the reply Rob. The next dry day I get I'll take the clutch apart and clean it up.

Springs huh? That is another odd thing about this mount.....there are no springs. My other two Cave Astrola mounts have springs and no grease. Do you have any idea how stiff the springs need to be?

Thanks,
Bill


It sounds like a previous owner left the springs off and tried to compensate for the stiffness by lubricating the clutch. I bet if you get some new springs and clean the grease off it will work much better. The springs need to be stiff enough to prevent the scope from slipping but light enough to move the scope around easily. You’ll have to experiment to find the right compression. Try light springs first and if they aren’t stiff enough try some slightly stiffer springs until you find a set that’s just right.


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