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Grease for LX200 baffle?

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#1 klyons

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Posted 25 September 2012 - 06:05 PM

I would like to re-grease my LX200 baffle to reduce image shift. Does anyone know what grease will work and is safe to use in the Meade tube? Thanks.

#2 Whichwayisnorth

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Posted 25 September 2012 - 08:21 PM

Here ya go. Click here

#3 klyons

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Posted 25 September 2012 - 08:39 PM

Thanks! Have you tried it?

#4 CORONA

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Posted 28 September 2012 - 12:54 AM

Don't mean to confuse you but the red grease that is available from Peterson Engineering is excellent. It looks like it is the same grease mead uses.

#5 imjeffp

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Posted 29 September 2012 - 10:52 PM

For some reason, I think the hi-vac grease is OEM. True?

#6 klyons

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Posted 30 September 2012 - 08:08 AM

In fact I recently contacted Pete Peterson asking if I could use their red grease (I still have some), and he stated that it should not be used on the baffle - it is not stiff enough.

#7 CORONA

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Posted 02 October 2012 - 12:18 PM

I'm going with the Hi Vac grease then.

#8 klyons

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Posted 07 October 2012 - 03:20 PM

Well I did go ahead and get the hi vacuum grease. I put it on the baffle tube and it did not change things much. I have always had a large amount of image shift (1/2 degree!), so it appeared that there was some other cause. I went back into the scope and removed the mirror assembly again. I observed that the metal assembly below the mirror (that is attached to the focus rod) was threaded on the shaft that slides onto the baffle tube. Above the mirror is a cork spacer, then more metal. The mirror seemed to be "loose" - the metal assembly below was not up tight against the mirror. I suspected that this gap caused the mirror to tilt. So I held onto the metal assembly below the mirror and rotated the shaft above the mirror to tighten everything down. The mirror no longer could shift, so I re-assembled everything back in the tube and checked it out. This turned out to be the problem - the image shift is very small, and the focuser knob turns very easily with no resistance. It had been harder to turn when the mirror was shifting in the loose assembly.
The mirror did rotate some when I tightened it, so I was concerned that the rotational alignment between the primary and secondary/corrector was lost. But the images I see have shown there is no degradation. If it did degrade I would just rotate the corrector to maximize image quality.

I have learned a lot from this exersize. Everything I have read about image shift referred to the grease issue - never have I seen comments about the mechanical assembly. If you are replacing the grease, you have the scope apart anyhow, and this is easy to check.

#9 CORONA

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Posted 09 January 2013 - 05:35 PM

About the Dow Corning High Vac Grease, is it good to use on all other parts of this scope instead of the red grease? or other lubes that are used in the gears etc.?
I got a tube of it and am thinking of removing all other greases and re-lubing with this stuff.
Any ideas?

#10 orion61

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Posted 09 January 2013 - 05:43 PM

I would like to re-grease my LX200 baffle to reduce image shift. Does anyone know what grease will work and is safe to use in the Meade tube? Thanks.

I have used SuperLube Synthetic grease mixed with a little Mobile One Synthetic SAE 40engine oil. It works very well because it can be mixed a bit thinner for us up here in the Minnesota Iowa area where actual temps can reach 30F Below actual temp. I have also used White P.A.O. Synthetic grease
it neither thins or thickens but is expensive about $12.00 for 2 or 3 oz..

#11 Qwickdraw

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Posted 09 August 2013 - 03:59 PM

I have huge image shift on a 12" LX200. I would guess it is as much as 3/4 of the FOV in just a 21mm EP. Does anybody have any photos or diagrams on how to disassemble the OTA to perform the greasing of the baffle and make the adjustments as outlined by klyons a few posts up? I don't want to go into this blind if I don't have to.

#12 rtanton

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Posted 10 August 2013 - 10:16 AM

Corona, the high vacuum grease is not your best choice as a lubricant. This grease is a vacuum stripped silicone polymer filled with fumed silica to increase its viscosity. It will work as a lube for non metal to metal contact. Its viscosity throughout a wide temperature range makes it well suited to damp between the baffle and primary in the SCT.

Pete is correct on his red grease. When I was at Meade, I had our guys try a high quality silicone lubricant. The SCT focused easily but would not hold position as the primary keep slipping.

Russ
former Meade and Dow Corning

#13 redlinedb16a

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Posted 10 August 2013 - 06:16 PM

I would like to re-grease my LX200 baffle to reduce image shift. Does anyone know what grease will work and is safe to use in the Meade tube? Thanks.

I have used SuperLube Synthetic grease mixed with a little Mobile One Synthetic SAE 40engine oil. It works very well because it can be mixed a bit thinner for us up here in the Minnesota Iowa area where actual temps can reach 30F Below actual temp. I have also used White P.A.O. Synthetic grease
it neither thins or thickens but is expensive about $12.00 for 2 or 3 oz..

Oil and grease will separate over time

So at one point you may have oil leaking onto your mirror

Perform a test
Leave a blob of grease in a jar untouched for awhile
You will see liquid oil around the grease

#14 redlinedb16a

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Posted 10 August 2013 - 06:17 PM

I will experiment with thin .005 thousands thick brass shim material to take up the slack

#15 P26

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Posted 11 August 2013 - 03:21 PM

For the record, that Corning product is a vacuum sealant and not intended as a lubricant.

#16 Qwickdraw

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Posted 12 August 2013 - 07:54 AM

Well, I got brave over the weekend and dismantled my entire 12" LX200 OTA. I was hoping to discover the cause of the large image shift. No such luck. After evaluating the construction I suspect the shift can be caused by at least two things...
1) the mirror actually tilting due force of the focusing arm tilting the outer tube as it travels up and down the inner tube.

2)I also believe that the inner baffle which is affixed to the back of the OTA could flex when the focus is used. The inner tube seems to be threaded into the back of the OTA by maybe 1/4" of thread connections. Either that threaded connection may have some flex and/or the whole back wall of the OTA may also be subject to a small amount of flex.

My image shift is very large. Roughly 2/3-3/4 of the FOV in a 21mm EP. It also seems to consistently travel in the direction parallel with where the angle of the focus arm is attached to the mirror so about at the 30 degree to 210 degree line.

I did not have any grease on hand yet but I wanted to get an understanding of the mechanics of the assembly.

The mirror locking mechanism is a large gear which when rotated opens or closes a collet which tightens around the inner tube preventing the mirror from wiggling.

I replaced the stock focuser with the Featherlight earlier. That offered no help on the image shift issue. I didn't think it would but I wanted the upgraded focuser anyways.

The whole image shift is as we know inherent to this design, specifically, not having uniform forces applied in radial directions while focusing.

Any grease applied can seemingly only temporarily cover up the symptoms.

Why is my image shift so much more than others? One can only assume manufacturing tolerances.

I am not satisfied in just accepting this issue and resorting to an electronic crayford as a work around. I have a Binotron 27 binoviewer which means adding the extra length/weight for a focuser is not really an option.

#17 nitegeezer

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Posted 12 August 2013 - 10:27 AM

I do not notice any shift in my 8", and a friend has a 12" and I don't remember any shift in it either. During alignment, when we center on a star, we defocus to make sure we are centered. I have never had my scope open so I can't comment there. With that much shift, how can you collimate? Is the secondary mirror off center?

#18 Qwickdraw

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Posted 12 August 2013 - 11:32 AM

I do not notice any shift in my 8", and a friend has a 12" and I don't remember any shift in it either. During alignment, when we center on a star, we defocus to make sure we are centered. I have never had my scope open so I can't comment there. With that much shift, how can you collimate? Is the secondary mirror off center?


Not sure, I have only had the scope a week and it has been overcast every night but one. The one night it was clear, I didn't attempt to collimate it.

#19 Qwickdraw

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Posted 22 August 2013 - 06:04 AM

Well, I have heard mixed reviews about reapplying grease but currently the scope is almost unusable.

I went ahead and ordered the grease as recommended above.

Grease

I hope this offers an improvement

#20 Qwickdraw

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Posted 23 August 2013 - 10:48 AM

The grease arrived yesterday, I am not sure if I like the consistency. It is more of a sticky sealing paste than a lubricant. In any event, this weekend will be tear down time for this scope. I hope to report good news soon but I have my doubts.

#21 P26

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Posted 23 August 2013 - 11:35 AM

As noted on my posting of 8/ll, the Dow product you have is a sealant and not a lubricant. I've still got a tube of it purchased for an evaluation 10 years ago when the old MAPUG forum mentioned it while searching for the best baffle tube grease. But I sure didn't and wouldn't use it on my scope.

#22 Qwickdraw

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Posted 23 August 2013 - 03:47 PM

Thanks Pete, Can you advise a product that is good for the job?

#23 P26

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Posted 26 August 2013 - 10:32 AM

My 10" Classic image shift wasn't all that bad so I never did follow up by regreasing its baffle tube. My lubricant study was primarially a search for the grease still used on our focuser, gears and clutch upgrades. The image shift problem never was fully investigated so regretfully I can offer you no suggestions regarding baffle tube grease.

After a talk with Russ Tanton about grease last week it occurred to me that the stiffer the grease the greater the "striction" and the greater the force required to push the mirror sled up and down the tube. And the greater the force on the offset mirror sled pin the greater the tendency of the mirror to shift.

So, while a stiffer grease might better inhibit mirror flop (the tendency for gravity to pull the mirror down against its natural stops) it may not help with mirror shift. We do know that having adequate grease reduces mirror shift. But there's a possibility that a light grease will work as well as a higher viscosity grease. Consider the hypothesis that while a stiff grease better resists forces that cause mirror shift a higher force is required to push the mirror into focus when using a "stiff" grease. The greater force may push the mirror held by the "stiff" grease the same amount as a lesser force will when using a lower viscosity grease. So the benefit of the higher viscosity grease is canceled out by the higher force required.

This is all just my speculation.

The root cause of mirror shift and mirror flop is the gap between the baffle tube and the mirror sled tube. While Meade's optics are wonderfully precise their machining is less so. And some scopes have more of a gap than others.

If I were to look to solving mirror shift problems on an individual bad-behaving scope I'd look into gluing shim stock into the internal circumference of both ends of the mirror sled tube so as to reduce the internal diameter by just .001 or .002 inches. Don't know just how tight/loose the fit normally is but a little trial and error would be called for even if one measures first.

Clear skies,

#24 Whichwayisnorth

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Posted 31 August 2013 - 01:27 AM

I had a 10" ACF that had such bad mirror shift that I ended up engineering my own solution which was to add roller bearings in four locations 90 degrees apart along the back of the mirror that I could adjust. Then I used the hi-vac stuff I linked in second post for everything to ride on. For anything like gears or focusers etc, use Superlube synthetic.

#25 Qwickdraw

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Posted 01 September 2013 - 08:12 AM

Today is the day, After ordering the high vac grease and then determining it was more for sealing than lub I read that Tri-Flow Red Grease is a suitable grease for this purpose. Having once already taken the OTA apart 100% to try to determine the cause of large image shift, I feel confident it is a fairly easy task. I will post results as soon as I have some clear skies to test. I did read where one person attached a laser to the outer baffle tube and focused in and out to determine the extent of image shift so maybe I will try that as a before and after test.






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