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Bearing mod procedure

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#1 btieman

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Posted 12 November 2013 - 10:44 PM

Alright, after recently bragging about reaching 2000 observing hours on my CPC1100 without a hitch, the other night when I turned it on, the hand controller flashed "initializing" then went blank. Turns out one of the RJ45 connectors had corroded and shorted out on what Celestron calls the PC/AG board. $31 to Celestron and they shipped me a new part and all is well again :)

I generally leave my scope under a 365 Telegizmos cover and this is the first time I've had it torn down in almost 2 years. Since it's open, I'm cleaning it up, regreasing, etc… I figure I may as well get down to the bearings and see if they need replacing as well. I thought there was a thread with pictures on how to perform the upgrade but, after searching the forum for a while, I couldn't find it. Does anyone have a handy link to a thread detailing the replacement?

Thanks!

#2 lengro

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Posted 13 November 2013 - 05:11 AM

On www.nexstarsite.com there is a detailed pdf describing the procedure with images, here is the link:

How To Replace Factory Original Nylon Azimuth Bearing Balls

#3 lengro

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Posted 14 November 2013 - 12:01 PM

I've also been thinking of replacing the vinyl balls with steel balls on my CPC925, as it initially runs very clonky/bumby (sorry for my English). I spin the azimuth a few times and then it's - almost - perfectly smooth.

However, I read somewhere that Celestron uses half vinyl/half steel balls on newer scopes. That makes me think that Celestron has decided that steel balls only in the long run is to hard on the trail they sit in.

Has anyone here some long time experience with this mod?

#4 SporQ

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Posted 14 November 2013 - 01:03 PM

Yes, it is very simple to do.

Setting the preload on the main bearing is the most important part. It is a very coarse thread and does not require much force when set correctly (as in no play and free movement).

It would be easy to clean your Nylon bearings if they are in good condition. I would not mix them myself as that is less balls for the races to ride on.

#5 astrovienna

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Posted 14 November 2013 - 10:44 PM

Hi Brian,

If you need any help with the bearing mod, just let us know. I did it about three years ago when my scope started having RA "excursions," and it's been absolutely fantastic ever since. I routinely get 20 minute exposures with HFRs of ~1.1 arsecs.

As mentioned above, the only trick is to make sure you tighten the main nut just enough so that there is no rocking in the axis. Too tight and you'll get binding leading to RA elongation.

Kevin

#6 btieman

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Posted 15 November 2013 - 07:36 PM

Hi Brian,

If you need any help with the bearing mod, just let us know. I did it about three years ago when my scope started having RA "excursions," and it's been absolutely fantastic ever since. I routinely get 20 minute exposures with HFRs of ~1.1 arsecs.

As mentioned above, the only trick is to make sure you tighten the main nut just enough so that there is no rocking in the axis. Too tight and you'll get binding leading to RA elongation.

Kevin


Kevin, will do! Just waiting for bearings to arrive :)

After 5 years and 2000 hours, I've got no complaints with how it's been running. I've done hour long exposures with very acceptable HFD values in the past. My biggest guiding problem is wind and seeing so I'm not sure if I'll see an improvement or not during my typical use. Anyway, timing works well. Needed to open the scope to replace a cheap board damaged by "normal" wear and tear. It's not much use setting it back up right away since we're having a new sliding glass door put in on the deck and the installer has said it would be much easier on him to have the scope out of the way. So, might as well tear it all the way down and clean, replace and regrease and get it ready for the next 5 years.

#7 Radiostar

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Posted 17 November 2013 - 04:42 AM

My 9.25 developed a "jerk" every few seconds while rotating so I decided to replace the bearings. The Nexstarsite instructions are very good. The only thing I can add is to remember to mark the cables and matching connections on the boards. The only thing I did different is use a PTFE grease to lubricate the bearings that is safe for rubber, plastic and metals, designed for high pressure load bearing applications. It was not as difficult as I imagined it would be and the scope runs great now.

#8 btieman

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Posted 28 November 2013 - 12:48 PM

The only thing I did different is use a PTFE grease to lubricate the bearings that is safe for rubber, plastic and metals, designed for high pressure load bearing applications.


The bearings I ordered arrived and I finally had a few hours to break the scope down. Definitely some black residue in the bearing track and on the bearings--much more than what's in the picture on the nexstar site, but still not so much I would be concerned. I carefully examined a large number of the nylon bearings and could find no flat spots or any that looked out of round.

What does appear to be different on mine than the pictures on the nexstar site is that my bearing track was packed with grease. I don't see any obvious grease in the picture on the nexstar site. Also, my track is smoother than I expected from the nexstar description. Feels like a lightly polished service and not "fine sand paper". The only bumps I feel are where dirt had built up around where the bearing touch. Rubbing a bit with a napkin breaks it up and wipes it away.

Has anyone else who's done this mod had grease on the nylon bearings? I'm debating now of repacking the bearings with grease like Eddie did instead of using a light oil. The bearings I bought are 440C stainless. If people have opinions, I'm listening :)

#9 lengro

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Posted 28 November 2013 - 03:55 PM

The bearings I bought are 440C stainless. If people have opinions, I'm listening :)


I look forward to hear how this project works out for you.
It worries me a bit that Celestron chose nylon bearings over steel bearings. Is it just as simple as nylon is cheaper, or could it be that wear can become an issue with steel bearings?

Anyway, good luck with the project.

#10 astrovienna

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Posted 30 November 2013 - 12:21 AM

Brian, I hope I'm not too late. The description of what you found is word-for-word what I found in my CPC1100. Grease, a bit of grime, no flat spots, no fine sandpaper, etc. With my stainless steel bearings I tested both Superlube (grease) and oil, and found oil gave a bit better RA tracking. I think the viscosity of the grease is just a little too high. And the guys who originally came up with the bearing mod have been pretty adamant that you want oil, not grease.

Kevin

#11 btieman

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Posted 30 November 2013 - 11:20 AM

The bearings I bought are 440C stainless. If people have opinions, I'm listening :)


I look forward to hear how this project works out for you.
It worries me a bit that Celestron chose nylon bearings over steel bearings. Is it just as simple as nylon is cheaper, or could it be that wear can become an issue with steel bearings?

Anyway, good luck with the project.


Lengro, At least for my use typical use, wear is pretty far from my mind. 2000 hours of use over 5 years with the vast majority of that use at sidereal rates = I doubt there'd be significant wear even without any lube. Think about industrial applications where bearings run at high rates with significant heat. Sure, the aluminum is soft and nylon can compress and shave, but there's not a scary amount of motion/force at play--even on a wedge.

I think the bigger danger with nylon is sitting under a static load for long durations. That's when I'd expect flattening to occur.

Other people's use cases may differ though. I hibernate my scope every session. When I wake it up, there's generally 2 slews over a small portion of the sky--one to focus on a bright star, and one to the target. The rest of the time, my scope is slewing at sidereal for many hours at a time. Someone slewing all around the sky for visual observing would have a different use pattern and a different wear profile.

Brian

#12 btieman

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Posted 30 November 2013 - 11:42 AM

Brian, I hope I'm not too late. The description of what you found is word-for-word what I found in my CPC1100. Grease, a bit of grime, no flat spots, no fine sandpaper, etc. With my stainless steel bearings I tested both Superlube (grease) and oil, and found oil gave a bit better RA tracking. I think the viscosity of the grease is just a little too high. And the guys who originally came up with the bearing mod have been pretty adamant that you want oil, not grease.

Kevin


Kevin, I opted for grease. I imagine oil would work better for auto-guiding, but my use case is such that the scope sits out in the weather (heat in summer) for long enough the oil might dry off the tops of the bearings. As I only usually do one or two short slews, not a lot of time for the oil to redistribute over the bearing after the scope has sat for a while.

Grease won't have that problem...so I went that route. Superlube is less stiff than the grease that was there. The best guiding I need is to keep a star on a 25 um slit but if the star dithers across the slit it doesn't hurt the data. Hurts s/n some as I lose light when the star's not there, but it's not like it ruins a 10 minute sub-exposure and I have to throw it away.

In all honesty, though, I believe any coating that will prevent the bearings from rusting will probably be sufficient for the amount of motion and forces at play.

Brian

#13 AhBok

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Posted 30 November 2013 - 11:25 PM

I bought the stainless steel bearings but have not done the mod yet. Does anyone have thoughts on alternating steel and nylon bearings, every other one? I believe someone posted the newer hd mounts are configured like this?

#14 Larry F

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Posted 01 December 2013 - 08:32 AM

Why would you want to do that? If the nylon bearings are more likely to get out-of-round, why leave any of them in the instrument?

#15 junomike

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Posted 01 December 2013 - 12:32 PM

I agree with Larry! Staggering nylon bearings in between the steel bearings is no difference than adding spacers and cutting the actual load support in half!.

Mike

#16 AhBok

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Posted 01 December 2013 - 02:38 PM

Thanks guys. The only reason for my question is this is what I've heard Celestron did on the new mounts. I'm curious as whether or not there is a functional reason for this or if it is purely economic.

#17 Larry F

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Posted 02 December 2013 - 06:52 AM

The first question is, is it true? The incremental cost of stainless steel bearings over nylon bearings is fairly minimal (you can get 100 1/4" balls for $4.95 retail...imagine sourcing thousands...they'll be less than a cent apiece). Even in China, the labor involved in making sure that the balls are alternating steel-nylon-steel-nylon etc. has got to take a few minutes and have a reasonably high error rate. So why not just pour one kind of ball into the mount? Seems to me to do otherwise is silly, but then again, sillier things have happened in the manufacturing world.

#18 AhBok

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Posted 02 December 2013 - 09:52 AM

Thanks for the information. I have the stainless steel bearings and was about to do the mod after reading several posts here attesting to the improved tracking. But then, I decided to research further and found statements like this from Boca Bearing company:
web page


Engineers often hesitate to use Plastic Bearings in their designs, because they have trusted steel bearings for years or they just don't think plastics can handle demanding applications or environments. Plastic Bearings, however, can endure extreme temperatures, heavy loads and high speeds. Some other benefits to Plastic Bearings are listed below.
Plastic Bearings can often lead to more freedom from maintenance. Their resistance to dirt, dust and chemicals make plastic bearings a set-it-and-forget-it solution. Plastic Bearings can reduce costs up to 25%. They can be highly wear resistance, with a low coefficient of friction and can replace more expensive alternatives in many applications. Plastic Bearings also do not typically need lubrication unless steel balls are used in combination with plastic races. Plastic bearings are designed to maintain a low coefficient of friction over the life of the bearing. Compared to steel bearings, which can become pitted and increase the coefficient of friction, plastic bearings many times last longer. And finally, Plastic Bearings can be used in wash-down applications, salt water and harsh chemicals without compromising performance. Water can even be considered as a lubricant for plastic bearings.


For me, I think this warrants me looking into this a little further before I make the mod. I use my CPC mostly for visual and am most concerned about long term durability and quiet slewing, as opposed to more accurate tracking.

#19 astrovienna

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Posted 02 December 2013 - 11:18 PM

AhBok - I don't think you should agonize over it. I imagine you'll get good results whether you use plastic or steel as your replacements. And at the very low speeds we use I doubt steel would ever wear out a bearing race.

To be honest, I'm not even sure the bearings are always the source of the problem, whether it's jerkiness, RA excursions, or ticking noises. In my scope (RA excursions, but no noise or jerking), the bearings looked just fine, so maybe the real problem was simply that the factory had over-tightened the main bearing nut. But in another CPC1100 I checked, the mount actually locked up several times as I tried to rotate it in azimuth, so that I had to give it a little shove to get it moving again. I didn't open that one, but I would guess that really is a case of bad bearings.

Whatever the cause, for most people the bearing replacement job, with the associated work, seems to have solved whatever problem they had.

Kevin

#20 AhBok

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Posted 02 December 2013 - 11:45 PM

Thanks Kevin. I'm not really agonizing about it--just curious about the trade-offs. I appreciate the info.






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