8 replies to this topic

[AstroNikko]

Hi folks,

 

What lubricant should you use with worm gear bearings? I'm reaching out because I'm questioning my own decision here. Could use some advice.

 

I'm rebuilding my Celestron AVX mount, and in the process am also replacing the worm gear bearings. The stock JESA 686Z bearings were over tightened, which I believe may have caused excessive wear as a result. I could feel the bearings grind even after adjusting the tension rings properly. It's also possible they just needed re-greasing, though.

 

The bearings I've selected as replacements are ceramic S686ZZ stainless steel bearings, which arrived dry. I didn't realize this at first, since they were advertised as being pre-lubricated with grease. When I installed them without lubricant, they spun fast and freely, but then seemed as though the bearing cage would bind up with the bearings.

 

I don't mind that they arrived dry, as this allows me to select my own lubricant, and apply the proper amount based on the use case. I ended up lubricating the bearings with Super Lube multi-purpose synthetic grease (NLGI 2) with Syncolon, only using a dab of it on the race between each ball bearing. This solved the binding issue. The bearings now feel super smooth, but they don't spin anywhere like the did before. Which I guess I should have expected.

 

So now I'm second guessing my decision. In this application, the bearings will only ever rotate at low speeds, and they'll never be under heavy load. Is Super Lube synthetic (NLGI 2) sufficient, or should I have selected a lighter weight grease, such as NLGI 1 or NLGI 0? Or should I have used oil instead of grease?

 

Image and video thread found here.

 

Thanks in advance,

 

Nikko

Edited by wcoastsands, 09 April 2019 - 11:11 AM.

[fgraus]

Have you contacted the people you bought the bearings from for advice? 

[AstroNikko]

Have you contacted the people you bought the bearings from for advice? 

Good idea. I did reach out on Friday about the issue with these particular bearings, but haven't heard anything back yet.

 

I just followed up with someone who responded to me earlier about a separate issue with the same order. In addition to the S686ZZ bearings, I had also ordered a 7007ACM bearing, but received a 7007C bearing instead. The main difference between the two is in the contact angle. Turns out the bearing I ordered wasn't in stock, so they substituted it with the more expensive bearing rather than cancel that part of the order, or put it on back order. I appreciated the quick thinking on the part of the person fulfilling the order, as well as the honesty of the person who helped me sort out the discrepancy. But now I'm wondering if the same was done with these 686 bearings.

 

Hopefully they'll respond back soon with something helpful. Thanks for suggesting that I reach out to them for lubricant advice.

Edited by wcoastsands, 09 April 2019 - 11:56 PM.

[EFT]

Never open the seals of a sealed bearing.  They are sealed for a reason, to keep the lubricant in and the contamination out.  It is also difficult to remove the seal and not damage it.  If these bearings have metal shields as opposed to rubber seals (the pictures on the website show both), then it is even more likely that the shield was damaged.  As a note, in our applications, rubber seals are the better choice.  They are better at keeping out contamination which is our largest concern.

 

From the manufacturer:

"10 Stainless Steel Bearings with Ceramic Balls ABEC-5 quality, It is a popular size that could be used in many application that uses this size 6mm x 13mm x 5mm, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease."

 

While the bearing may look dry, it is not.  Close it back up and leave it alone.  These bearings are not packed with thick grease.  They are lubricated with a fine oil and are otherwise self lubricating.  Car wheel bearings are packed with thick grease due to the high speeds and temperatures involved so people tend to think that has to be how bearings must always be.  That is not necessary for our purposes.  About the only time that I replace bearings (axis bearings since I always replace worm bearings) is when they have been opened and messed with resulting in contamination that effects the turning of the bearing.  I can't recall having to replace a bearing due to defect more than once or twice (damage yes, defect no).

 

For telescope mounts, we are worried about smooth, precise movement.  We are not worried about turning hundreds and thousands of RPM and generating high heat.

[AstroNikko]

Thanks for the feedback, Ed. I appreciate it.

 

I do agree that permanently sealed bearings should not be opened, at least if the intention is to reuse them. These aren't permanently sealed though, which might further indicate that these might not the bearings advertised. These bearings that I have in hand have removable shields held in place by a c-ring, or snap wire. They do not have permanent press fit shields. The stock JESA 686Z bearings also have removable shields.

 

 

This is one of the new S686ZZ bearings:

 

 

 

And this is the stock JESA 686Z bearing that originally shipped with the mount:

 

 

 

The reason I opened the bearing in the first place was because movement was not consistently smooth. Something was binding in the race. Being that the shields are removable, I took a chance on the one I was having issues with. I found there to be no grease or even oil in the bearing. The other bearings I received were all coated in oil. These appear to be dry bearings. The bearing cage is loosely fit, and is free to wobble around the inside of the bearing. I suspected this was the source of the issue, and that a little lubricant would solve it.

 

I opted for grease in this case instead of oil because I didn't want the lubricant to migrate. And I figured even with the speed reduction with grease, it's probably still more than fine for worm gear bearings. Grease would protect and coat the surfaces better and longer than oil would. Only a little bit is needed, though. And that's all that I applied. It seems to have fixed the issue with the bearing binding up. It now moves super smooth, albeit a lot slower than before.

 

 

 

I guess what I'm still wondering is if I should have used a lighter weight grease than a Class 2 grease. This may be a "try it and find out" sort of deal.

[EFT]

A rough bearing would certainly imply an issue with the bearing.  The key in this case is whether or not you see tracking problems in that axis that suggest a defective bearing.  I wouldn't worry too much about the grease or how freely or not the bearing spins at this point.  If you install the worm so that it spins freely, then you haven't put enough preload on it anyways.  There has to be some preload to avoid endplay in the worm.  That preload will slow down the spinning itself.  The problem with stock bearings is that they always install them with too much preload which ends up damaging them.

[AstroNikko]

Thanks, Ed. That sets my mind at ease as I've come to a similar conclusion. So that's reassuring.

 

I got a response back from the supplier this morning. They said the bearings that I ordered were out of stock, so they exchanged them with the same bearings but dry. They didn't offer any suggestions on lubricant, though. I think I'm happy with using Super Lube synthetic NGLI 2 for now.

[SteveGR]

Thanks, Ed. That sets my mind at ease as I've come to a similar conclusion. So that's reassuring.

 

I got a response back from the supplier this morning. They said the bearings that I ordered were out of stock, so they exchanged them with the same bearings but dry. They didn't offer any suggestions on lubricant, though. I think I'm happy with using Super Lube synthetic NGLI 2 for now.

It would have been nice if they had informed you of the substitution.  Maybe they were hoping you wouldn't notice?  Sheesh.

[EFT]

The certainly wasn't good of them to send you a set of dry bearings without telling you.  While it would not have made a tremendous amount of difference in our application, in some other application that might have caused a critical failure.  That's about as bad as sending you a non-ceramic bearing and thinking it was OK since they were the same size.  I have never had VXB do that to me before.