How Should These Spindle Bearings Be Lubricated? Also, What Bearings to Buy?

[ChandlerJPerry]

The approach of basing the grease base oil thickness off the oil requirements for a similar application clicks for me, as the bearings in my spindle should have similar service requirements to a Bridgeport.

To that end I went looking around and found this ISO 46 offering from Lubriplate that seems readily available. Small 50g tube available from many retailers for around $10. Attached is the data sheet. A quote from it reads; "LUBRIPLATE DS-ES Lubricant is also highly recommended as a bearing lubricant for electrical motors, spindles and other mechanical devices where low torque, high speeds and long life are essential."

I also found an ISO 32 grease from Mobil called Mobiltemp SHC32 that looks like a great candidate as well, and a 12.5 oz tube goes for $13 from McMaster. I would say presently I'm between these two as more economical alternatives to Kluber.

I have no opposition to Kluber products other than price. I was going to take a look at their other offerings to look for a thicker grease than NBU 15, but their data sheets are locked behind needing a login to their site. Also their product search is very difficult to navigate, and I decided at that point to move on to other possibilities.

 

[Ischgl99]

Either one of those should work. The Lubriplate grease is an NLGI 1, so that is a bit runny for a vertical spindle at the speeds a mill runs at. The Mobil is not much better at 1.5. For the speeds this machine can run at, an NLGI 2 might be a better choice since this is a vertical spindle, so if you find the grease runs out too easily over time, you might need to increase the NLGI.

Kluber is frustrating with how they restrict access to info. I used to have a login, but can’t remember it.

 

[Ischgl99]

Another option is Mobilgrease 28, it’s available at McMaster-Carr and is a good fit for spindles.

 

[ChandlerJPerry]

I am definitely going to try out the Mobiltemp SHC32. I found an applications guide (attached to my post) from Mobil that specifically calls it out for spindle bearings and machine tools. I do agree with the concern about it running out since my spindle is not sealed, but I'm willing to give it a try and see how it performs.

Unfortunately this machine has no grease fittings or way to add grease without removing the quill/spindle assembly, so no matter what choice I make relubrication will be a chore.

 

[Ischgl99]

Thanks, that’s a nice chart, I saved that to my files. They don’t have the Mobilgrease 28 listed, I’m wondering if the Mobiltemp 32 is an updated version of that. In any case, sounds like you have a good plan and that grease should work well.

That’s unfortunate you don’t have a way to regrease the spindle, hopefully you come across a manual and there is an easy way to do it that is not apparent right now. One thought, since the bearings are open, maybe you can regrease from the top near the pulley and let the grease work its way downward. That would avoid removing the spindle, but might need to pull the pulley off to get the grease in there.

 

[ChandlerJPerry]

I received everything in the mail and was able to spend some time working on the spindle this evening.

Step 1 was to knock the burrs off the spindle created by the old bearing spinning. A needle file made short work of it.


After that I dropped the thrust bearing washer on.



Next I cleaned out the new spindle nose bearing with some isopropyl alcohol to remove any lingering preservative and greased it with the Mobiltemp SHC32. My weapon of choice was a 3cc syringe with a fine tip on it. NSK recommends 2cc of grease on a 7208 for a 15% fill. I went with more like 2.5 to shoot for 20%. With the small tip it was easy to apply the grease directly between the balls on the inner and outer race.



Then I applied some loctite 660 to the shaft. I was surprised to find it's a very viscous paste, unlike the usual runny retaining compounds I've used from loctite.


After spreading it in a thin layer around the worn area, I installed the bearing with a twisting motion as recommended. Recommended cure time on the tube is a few hours so I left it alone at that point.

Now for one last mystery regarding the bearing arrangement on this spindle! While looking over the old parts I realized the 6208 ball bearing is in fact an angular contact bearing. Or at least some kind of bizarre hybrid. Whether this is by design or kludging by the last guy, I have no idea. But looking at the outer race it is clearly shaped as an ACB race would be and bears a 7208 part number instead of of the 6208 on the inner race. I have no explanation for the mismatch between the two. Or why it would be an ACB because the spindle as set up has no way to preload that bearing.



This has me seriously wondering if the spindle nose is supposed to have two ACBs in the same thrust direction with a spacer between the inner races that was discarded whenever these bearings were last replaced.

I am debating on if it would be worthwhile to attempt such a configuration, because as coincidence would have it the outer race spacer that I do have is .707", which is the exact same thickness as the inner race of the now disassembled bearing I was examining. Meaning I would have a perfect spacer for the inner races if I wanted to do so. I could also acquire an identical RHP bearing to go with the one I already purchased. Not sure if it would provide any benefit, although it seems more logical than how it is currently set up. I already have a 6208 in hand that I ordered, I'm just utterly perplexed by the combination of ball bearing inner race with ACB outer.

 

[extropic]

So far, so good. I really appreciate the clear images.

Hybrid bearing? Aren't you kind. Calling it a kludge is a euphemism.

Achieving the "exact" height and parallelism of spacers, to set a desired preload for a pair of ACBs, is a non-trivial task.
I understand that ACB pairs can be had with OEM preload set at the factory. That simplifies the spacer issue because the inner and outer only need to be exactly parallel and equal in height to maintain the OEM preload. You might ask a bearing distributor. Be seated when he replies with the $$$.

 

[ChandlerJPerry]

Hybrid bearing? Aren't you kind. Calling it a kludge is a euphemism.

Abomination, crime, affront, and disgrace all come to mind but I'm trying to maintain some semblance of positivity here .

 

[Ischgl99]

That is very strange, I don’t think I have ever seen a bearing like that. 17208 is not a standard designation, so I am wondering if that is a custom bearing made for this machine, or someone found a bearing somewhere online from an offshore supplier and thought it was what they needed.

When mounting bearings in tandem, they are usually right next to each other so you don’t need precision spacers. Mounting that way would increase the axial and radial capacity, but I would expect them to be mounted without spacers instead of how this spindle is designed. If you want to use tandem mounting, the snap ring makes sense to keep everything together while mounting, but you’ll need spacers for the inner and outer rings. This machine gets more confusing every time you post lol.

 

[ChandlerJPerry]

No matter what path I choose, I think I will have to omit the snap ring on account of the fact that the thrust washer raises the bearing stack slightly and partially obscures the snap ring groove.

I've come up with two mounting schemes for double ACBs in the spindle nose. Pictured here as a doodle:


Personally, config A appeals to me as it eliminates the need for two precisely matched spacers pictured in config B and would allow for the ACB inner races to be preloaded. Both configs would have the bearings with the same thrust direction, with the opposite thrust taken up by the 7307 at the top of the spindle. I have found that the existing spacer that I have is somewhat dimensionally inconsistent in terms of thickness. However I could use the previously pictured 17208 outer race as a spacer for config A, I would expect it to be very parallel and flat since it is a bearing race. It is also within a thousandth or so of the thickness of the current spacer, so the stack height wouldn't be significantly impacted.