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G-11 Right Ascension axis tension

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#1 TomN

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Posted 16 March 2009 - 11:48 PM

I've heard this mentioned before, but not the remedy....my G11 requires a lot of tightening of the knurled collar on the right ascension axis to provide any level of tension - basically it cannot be tensioned to a significant degree. Is this just an impression due to the extra lever arm on the RA axis or is something amiss? Of course, this problem requires exacting balance on the axis.

Is this tension problem normal, or is there a way to adjust that tension?

#2 blueman

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Posted 17 March 2009 - 01:35 AM

There may be grease on the clutch plates, you might want to disassemble and inspect them.
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#3 Luigi

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Posted 17 March 2009 - 02:31 PM

On my G11, there was and is grease on the plastic clutch plates. You need to add levers to the tension knob to be able to tighten it sufficiently. Losmandy sells these. I added some myself.

#4 blueman

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Posted 17 March 2009 - 09:55 PM

There is not suppose to be grease on the plates, clean them with alcohol and reassemble them. You are never suppose to be able to lock the clutch, it is always going to move if you hit it. If they did lock, and you ran into it, you would probably damage something.
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#5 Strgazr27

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Posted 17 March 2009 - 10:25 PM

I had the same issue with my G11. While I had the mount apart for a cleanup and re-lube I figured I would take care of it. The first issue was the Teflon disks had grease all over them. I also noticed that when I took a mchinists level to the disk that actually applies the pressure there was a significant low spot in the center. What this meant was I was getting pressure applied from basically the outer 1" of disk. I took a bodywork file and carefully worked the disk over till it was nice and flat. I re-assembled the mount and it was night and day. I have the upgraded clutch knobs on mine and even so, it was like a new mount. Floyd is also correct. You want just enough tension to prevent slipping with your payload but not so much that the clutches do not do what they are designed for.

#6 Jason Glass

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Posted 18 March 2009 - 12:06 AM

I also noticed that when I took a mchinists level to the disk that actually applies the pressure there was a significant low spot in the center. What this meant was I was getting pressure applied from basically the outer 1" of disk. I took a bodywork file and carefully worked the disk over till it was nice and flat.


Hi Bobby,

I am curious if you ever use the mount for push-to operation since your mod and if you've noticed more stiction in its motion? I ask because I recently designed and built a mount using a PTFE disc sandwiched between aluminum plates (similar to DiscMount), and I'm interested in the results of similar setups with different surfaces in contact for braking/clutching action.

Having done routine maintenance on my own G11, I'm fairly certain that the outer 1" of the pressure disc coincides with the location of the large-diameter roller thrust bearing on the other side of the large worm hob gear.

The design tolerance surely allows for that center depression in order to compensate for flexure as the clutch parts are pulled together via the main axial shaft, and to keep the hob gear from deforming under axial load on its unsupported center portion.

Breaking the smooth, hard anodized surface with a file is most likely why your mount is clutching tighter now, since raw aluminum is known to have drastically lower lubricity than class III anodizing. This can be an advantage if you're strictly using it for GOTO operation with near maximum loads. Unfortunately, a microscopic layer of aluminum oxide smut constantly builds up on all unprotected aluminum surfaces and gets pushed around by anything in contact, increasing wear rate of all the parts.

FWIW, the outer inch of the disc encompasses a great percentage of the total surface area of the disc, and has the greatest clutching leverage of any portion of the disc.

I'm glad the tune-up is working well for your application. I hope you'll keep us posted on its performance when more of your great images start coming in!

#7 Luigi

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Posted 18 March 2009 - 06:55 AM

I always used my G11 as push-to. Smooth operation of the clutch is essential. I bought 10+ years ago and there was no question that it came from the factory with the clutch surfaces amply greased, and I suppose that was to make push-to smoother and with less stiction. I never was unable to tighten the clutch enough to prevent un-intended movement of the scope. Putting levers on the tension knob made it easier. The first time I opened it up I cleaned off the grease and the amount of stiction was unacceptable. Try grease, or no grease, and perhaps even different clutch materials (HDPE, Teflon, etc.) to get the action you want. Don't make any irreversable mods until you're sure that's the way you want to go. :)

#8 Strgazr27

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Posted 18 March 2009 - 01:03 PM

Jason,

I am curious if you ever use the mount for push-to operation since your mod and if you've noticed more stiction in its motion? I ask because I recently designed and built a mount using a PTFE disc sandwiched between aluminum plates (similar to DiscMount), and I'm interested in the results of similar setups with different surfaces in contact for braking/clutching action.


I have not and will not be using the mount in a push-to mode. Everything I do is via GoTo. I have seen your masterpiece and it is amazing to say the least!

The design tolerance surely allows for that center depression in order to compensate for flexure as the clutch parts are pulled together via the main axial shaft, and to keep the hob gear from deforming under axial load on its unsupported center portion.


I don't think you'd be putting enough pressure to worry about that happening. I tighten the clutches so that it is difficult to manually move the setup but in the event of a moment of stupidity or the safeties fail, the clutches will break free.

Breaking the smooth, hard anodized surface with a file is most likely why your mount is clutching tighter now, since raw aluminum is known to have drastically lower lubricity than class III anodizing. This can be an advantage if you're strictly using it for GOTO operation with near maximum loads. Unfortunately, a microscopic layer of aluminum oxide smut constantly builds up on all unprotected aluminum surfaces and gets pushed around by anything in contact, increasing wear rate of all the parts.


Your correct and the increased clutch grab is just what I was looking for with the loads I am using. I also didn't want to worry about it slipping 4 hours into a run of exposures Lol. I am really OCD about my stuff and I'm sure the mount will be pulled apart again for a cleaning and tuneup long before any buildup of oxides could occur. And you never know with me......That CGE Pro is looking better all the time Lol.

I'm glad the tune-up is working well for your application. I hope you'll keep us posted on its performance when more of your great images start coming in!


Not a problem :) I can tell you that I was out last night and my latest PemPro run shows a PE of 2.1/ .7 :) So I'm pretty happy with it right now. That was at an image scale of 1.85 arc seconds/pixel.

#9 Todd

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Posted 18 March 2009 - 07:31 PM

I wrapped my knobs with hockey tape so that I can get a good grip on them. Cheap and it works. ;)

I never was unable to tighten the clutch enough to prevent un-intended movement of the scope. Putting levers on the tension knob made it easier.



#10 TomN

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Posted 19 March 2009 - 08:25 AM

What is required to disassemble the mount and clean the clutches? Is it straightforward? Can anyone provide simple instructions? Thanks!






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