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

[markba633csi]

The wear on the spindle portion looks too be so little that perhaps you could use that Loctite product that fills gaps.
The wear on the shoulder part below that would of course need to be reground- but epoxy might be a possibility, or just turn down
with a carbide bit- provided you have a lathe

 

[ChandlerJPerry]

The wear on the spindle portion looks too be so little that perhaps you could use that Loctite product that fills gaps.
The wear on the shoulder part below that would of course need to be reground- but epoxy might be a possibility, or just turn down
with a carbide bit- provided you have a lathe

Which loctite product are you referring to? I'm not familiar with it.

EDIT: I did find this and it seems like it may be what you mean?

LOCTITE® 660

If you want a product that enables re-use of worn bearing seats, keys, splines or tapers, try LOCTITE® 660. This high-strength retaining compound is designed for the bonding of cylindrical fitting parts, particularly where bond gaps occur – and without the need for re-machining. It’s also...

next.henkel-adhesives.com

I know loctite also makes a myriad of the green flavored bearing retaining compounds like 680, some suitable for loose fits, if that's what you meant.

 

[markba633csi]

411 and 660 are two I have heard of- may be others

 

[extropic]

I've been watching and I see plenty of "right thinking" IMHO so far, but I'll add my own to the suggestions.
I'm assuming that the "quill end nut plate" can actually secure the two outer races, the outer spacer and the outer spacer is precisely parallel.
consider using a pair of 7208 ACBs, back to back, in the lower positions. Discard the snap ring. Machine an inner spacer that, when clamped, will set the preload on the ACBs. Machine an appropriate spacer to fit between the upper 7208 inner race and the inner race of the uppermost bearing. Use a 6307 radial bearing in the uppermost position. Use the existing nut to clamp all the inner races.

Regarding the circular groove damage to the spindle bearing shoulder: If you have access to a quality grinder hand, and the price is acceptable, the best repair is to grind to 100% cleanup. The spindle will sit a few thou higher in the quill but I doubt that would be a problem. Another option is to make a washer to cover the damage. I might start with a thrust bearing washer which is already hard, flat and parallel. The only modification is to reduce the washer's OD as required.

I would use a sealed bearing for the uppermost position (6307). It's a milling machine and I don't want contamination screwing things up.
I would machine (remake?) the quill end nut plate to carry a lip (or felt) seal for obvious reasons.
If the quill is without any unsealed holes, open, grease lubed ACBs should be fine. The quill interior has to be sealed from ingress of anything that could contaminate the open ACBs/grease.

Good luck.

 

[ChandlerJPerry]

@extropic thank you for your detailed reply! I think that sounds like a fantastic plan to rework the spindle in a more sensible fashion. I do think it's a little past my current abilities to accomplish with my lathe also being down. I am definitely putting a pin in the idea for the future though.

However I did want to comment that I love the idea about using a washer to cover the spindle damage. I had the same concept myself but I hadn't been able to come up with a suitable washer, a thrust bearing washer is a perfect fit. I did contact a local grinding shop today and they would like me to bring the spindle in for them to get a look at it early next week. I would prefer that course of action but I am on a pretty tight budget, so the washer idea may end up being what I pursue.

I am thinking that idea plus an application of loctite 660 for the lower bearing is going to be my lowest cost way to hopefully get things back to a baseline state to at least measure where I'm at in terms of runout, have a functional mill for now, and make a plan of attack from there.

 

[extropic]

I forgot to mention before. If you end up using a washer, be sure to stone the burrs off of the spindle damage. I think I can see raised burrs in the very good images you posted.

Please let us know what the grinder quote is because I have no idea what to expect. $100?

I completely understand the near term "let's get it running sooner" vs the "fantastic plan" approach.

 

[ChandlerJPerry]

Feeling like I have nothing to lose at this point, I decided to put the spindle back together and check the runout. I cleaned all the old grease out of the bearings and put some fresh #2 bearing grease in them. Unfortunately it looks like these bearings are shot, or maybe just lacking in precision.



Even with preload to the point that there is considerable drag on the bearings, I'm measuring .001" on the spindle taper. Here is a video of the runout being measured. Pay no mind to the dings in the taper

As I see it right now, the lowest cost option to get myself to a well functioning mill again is to pursue the concept of the thrust washer over top of the shoulder that @extropic suggested, combined with the loctite 660 to hopefully take up any slack that may exist between the spindle and inner bearing race. At least one thing in my favor is that there is a thrust washer available in the exact size I need, 40mm bore x 60mm OD. This is a perfect match for the shoulder, I am thinking the 1mm thick option would be sufficient.



Combined with some ABEC 5/P5 bearings, I'm hoping I could at least get it back down into the tenths.

I will still likely take the spindle to get a quote on grinding, but I think bearings just ate that potential budget up.

 

[Ischgl99]

I like the washer idea, that is worth a try. Maybe try the washer with the old bearings first and see what that does. If the shoulder is not square to the spindle axis due to the wear, that could be causing some of the runout you are measuring. With the wear on the bearing seat, there is no guarantee the Loctite will center the bearing, the ball bearing may help with that, but you need to make sure the inner ring is centered while the Loctite is drying. The loctite is more meant to keep the inner ring from spinning on the shaft and doing more damage, so you probably are not going to see the potential of precision bearings without the spindle in good condition. My preference would be fixing the spindle before new precision bearings. Even standard precision bearings on a good spindle is likely to give better results than precision bearings on a worn spindle.

If you choose to fix the spindle and go with standard precision bearings for the time being, if they are available in the size you need, the FAG X-Life series bearings are made to P6 tolerances in several areas, but come at standard precision prices. SKF does the same with the Explorer series.

 

[ChandlerJPerry]

With the wear on the bearing seat, there is no guarantee the Loctite will center the bearing, the ball bearing may help with that, but you need to make sure the inner ring is centered while the Loctite is drying. The loctite is more meant to keep the inner ring from spinning on the shaft and doing more damage, so you probably are not going to see the potential of precision bearings without the spindle in good condition. My preference would be fixing the spindle before new precision bearings. Even standard precision bearings on a good spindle is likely to give better results than precision bearings on a worn spindle.

That is a very good point. To that end either tonight or sometime this weekend I will disassemble it again and see if I can take some micrometer readings from the spindle to better assess the condition the bearing seat is in.

Visually the wear on the bearing seat looks pretty minor, but I know looks can be deceiving.

Speaking on bearings, I wholly agree with you @Ischgl99 in regards to using non precision bearings. However I did some part number research last night and came across a few NOS candidates on eBay at incredibly favorable prices. I would appreciate a sanity check though to make sure I've got the right specs. My feeling is that at these prices, why not spring for P4 spec? Furthermore, at said prices I may even be able to pursue spindle grinding depending on what that looks like cost wise.



I love cheap and am often constrained to it, but I know this is one instance where making it right if I can will pay off.

Is there any reason to choose a precision grade bearing to replace the radial bearing? It seems almost vestigial at this point based on the discussion.

 

[Ischgl99]

I honestly don't know what the radial bearing is doing, so I'm not sure if it would make a difference or not.

I used to work in the bearing industry, they estimate 10% of the bearings sold worldwide are counterfeit, so I avoid buying bearings on Ebay or other non-authorized distributors. The first bearing you show is selling for 10% of the normal price, that is a huge red flag for me. You can go to this website and scan the bar code of the bearing box of the second listing and it will let you know what that bar code belongs to and if it matches what is on the bearing. https://www.stopfakebearings.com/ Look and see if there is high spot markings on the bearings, I know NSK does that on their precision bearings, so if that is missing, then it should be a hard pass. You might not be able to see it in the pictures, maybe you could get the sell to get you better pictures.