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Damping grease on the main baffle tube? (C8)

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#1 NMBob

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Posted 28 March 2017 - 01:16 PM

I got a tube of damping grease (Nyogel 767A) and I've been putting drops of it here and there...the manual elevation/declination threaded shaft on a couple old C8 mounts, the threads of the objective ring and locking ring of the 9x50mm finders, etc. Everything is starting to feel so smooth and luxurious and expensive that I'll soon be afraid to take the stuff outside. :)

 

Should this be used as the main grease for the main mirror on the outside of the baffle tube, or should that stay (in my case) Super Lube and just use the damping grease on the threaded focuser bolt? I won't have a motorized focuser or anything on this scope.

 

Thanks!

 



#2 HenryB

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Posted 28 March 2017 - 01:34 PM

I have used damping grease for years without problems on a C11. It works, but do not expect the grease to reduce image shift when focusing.



#3 leveye

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Posted 28 March 2017 - 01:35 PM

Might give the focuser a bit sluggish feel with that application. Then again it may cure any and all mirror flop as well. I'm interested what you discover. Keep us posted.


Edited by leveye, 28 March 2017 - 01:35 PM.


#4 msl615

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Posted 28 March 2017 - 02:01 PM

I will be following your findings, and applying similar ideas to the ETX 125 series. My issue is that my observing temps are extremely low (Fairbanks, Alaska) and have to handle -20F to -30F...regular OEM grease turns to glue and it is almost impossible to focus these mechanisms. I use Dow Corning Molykote 33 which works well down to -40 and beyond on mounts and other optic trains. But, it does not have much damping to it.  I will be regreasing a 125 sometime in the next month, and while it will not get that cold here outside in that month, I will be testing by putting the 125  into a large freezer. 

 

Mike



#5 Paul G

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Posted 28 March 2017 - 03:33 PM

I will be following your findings, and applying similar ideas to the ETX 125 series. My issue is that my observing temps are extremely low (Fairbanks, Alaska) and have to handle -20F to -30F...regular OEM grease turns to glue and it is almost impossible to focus these mechanisms. I use Dow Corning Molykote 33 which works well down to -40 and beyond on mounts and other optic trains. But, it does not have much damping to it.  I will be regreasing a 125 sometime in the next month, and while it will not get that cold here outside in that month, I will be testing by putting the 125  into a large freezer. 

 

Mike

 

Nye has damping greases for a variety of temperatures.



#6 NMBob

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Posted 28 March 2017 - 03:51 PM

Good idea. I just put some on a simple nut and bolt and put it in our break room freezer. It's just normal food temperature, but it was pretty stiff when I took it out. As I moved the nut back and forth the grease just seemed to sort of ball up and disappear like there wasn't even any grease. Now that it is warming up it is going back to the way it felt when it was warm. That's not good. This 767A is good to 0C. I guess they are not kidding. That wouldn't be a big problem for here, but I'd maybe not want to put it on the mirror tube, but just the knob. They have others:

 

http://www.nyelubric...mpinggrease.pdf

 

Someone sells a kit of the 868 versions for $99. They are listed as being for things like telescopes.



#7 rmollise

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Posted 28 March 2017 - 03:56 PM

A little grease on the baffle tube is fine. More than a little and your mirror will drift through focus. Focus will continue changing when you stop turning the control. ;)



#8 msl615

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Posted 28 March 2017 - 07:29 PM

Uncle Rod, 

100% agree in the cold, and from your past excellent writings and blogs, this is a big issue when focusing clockwise (the mirror moving down the tube essentially sliding with gravity down the grease). I can reach focus as it is slowly sliding down the now very viscous grease,  and then right on past focus.  Following your past advice, the solution I follow at the moment is to focus in the cold moving counterclockwise 

My ultimate solution is that I am changing focusers over to Crayfords off the visual back.  I have that on a Terabeam now, and only use the regular focuser maybe once a night to get it close....then all observing is done by focus with the Crayford....so much better. 

 

 

Gus: I am going to look up about the Nye damping greases for different temps....thanks for that tip.   From their www site, it looks like they have several that are good to at least -40.  

 

Mike



#9 HenryB

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Posted 29 March 2017 - 06:26 AM

I used Nye damping grease on my C11 about 20 years ago. I ordered a sample kit from Nye that included 8 samples of a different viscosity. Each container is enough to do dozens of SCTs so I experimented to find the best. I can verify that the thickest samples cause too much resistance and make the focuser knob stiff.  In all cases, the image shift was still there but with the right viscosity the focuser had a nice feel to it.



#10 NMBob

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Posted 29 March 2017 - 09:41 AM

I sent in a request for samples yesterday. I had been gravitating toward the 'heavy', more sticky types, but after putting that bolt in the freezer I think you are right. After getting it to move (was stiff) it just felt like there was sand in the threads. I forgot to take the two nuts/bolts home and try it there with SuperLube on the other nut/bolt.

 

I'm not worried too much about the mirror flop on this scope. It will just be for outreach stuff. It's funny that they've never fixed that problem.



#11 EFT

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Posted 29 March 2017 - 11:55 AM

A little grease on the baffle tube is fine. More than a little and your mirror will drift through focus. Focus will continue changing when you stop turning the control. wink.gif

Rod is correct.  You don't want to slow down the movement of the primary since the focus shift will become a problem.  Stick with the Superlube on the baffle and add a little damping grease on the focus mechanism shaft if you feel it is really necessary.



#12 NMBob

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Posted 29 March 2017 - 01:47 PM

 

A little grease on the baffle tube is fine. More than a little and your mirror will drift through focus. Focus will continue changing when you stop turning the control. wink.gif

Rod is correct.  You don't want to slow down the movement of the primary since the focus shift will become a problem.  Stick with the Superlube on the baffle and add a little damping grease on the focus mechanism shaft if you feel it is really necessary.

 

 

Sounds good! I redid my '79 C8 a few weeks back before I got the damping grease. The focusing feels a little...cheap...or loose. I guess I did a good job of putting it back together -- no binding. I thought I'd try the damping grease out on this second one I'm working on. I'll wait and see if they send me some lighter versions. The mirrors have always shifted. My psychiatrist taught me to put the axe down and just look at it as a "feature". It hardly bothers me at all anymore. crazy.gif



#13 NMBob

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Posted 31 March 2017 - 12:10 PM

Finally got both bolts/nuts and both tubes of grease in the same room at the same time. The bolt/nut with the Nyogel 767A behaved like it did before when put in the freezer. Not well. The Super Lube (grey tube Synthetic Grease) did fine. Was only slightly thicker when cold, but it gave nowhere near the luxurious and expensive feel of the damping grease. :)

 

Still waiting to hear about the Nyogel samples...

 

Will get my C8 back together this weekend with just the Super Lube.



#14 NMBob

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Posted 03 April 2017 - 01:43 PM

Oh, just got the sample kit. (Couldn't figure out what that UPS box was. smile.gif)

 

One interesting parameter is missing from the pamphlet...the temperature range. That's an interesting thing to leave off. I'll look 'em up and test a couple.

 

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