What does the -A -B -C suffix mean for bearings?

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gregreid

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I have a Chinese MX-210V mini-lathe and want to replace its spindle bearings. I haven't taken it apart yet, but I understand from perusing YouTube about this lathe that it uses common 30209 tapered roller bearings at both chuck and drive ends. (Please let me know if you know differently, or if you know of an angular contact bearing that would be better.)

When sourcing 30209 bearings, I see various suffixes of -A, -B, -C and -M for them from various manufacturers, but I can't find anywhere that tells me what they mean. They all look the same and all have the same specifications (near as I can tell). Can anyone enlighten me? Maybe tighter tolerances? Harder materials?

Thanks,
Greg
 
Those letters are usually manufacturer specific and could have a different meaning from one brand to another. If you have a part number 30209A or 30209B, for example, that usually means there was a design change to the bearing. The important dimensions will still be the same, so it would be interchangeable with any other 30209 bearing, but the A design would be retired and anything new would be the B design. A different manufacturer might not have made any changes yet for their bearings, so it’s not that important between brands.

This document shows what Timken uses for their bearings:

 
I replaced the headstock bearings in a MX-210 before, and from my experience, I don't think you need, or want, close tolerance bearings. The bearings are quite large compared to the size of the lathe, and the loading it sees, and overly tight bearings can cause binding unless the bearing bores are likewise held to tight tolerance, which is suspect on that machine.

Looking back through my purchase history on Amazon suggests my lathe used 30206 bearings, not 30209. That's curious. They could have changed them, of course, so dismiss this comment as appropriate.
 
So C1 C2 c3 or the clearances for the bearing so a C1 is super tight, a C2 is a tight fitting. I use that on my travel on my table milling table. A c3 is a looser fitting. Usually a general fitting these days. If I remember correctly, CN is a normal but c3 is becoming the de facto standard in a lot of applications. It allows for heat not as precise
 
Thanks for all of the quick (on Christmas!) replies, everyone. And ho ho ho.

Looks like I'd better take my lathe spindle apart and see what's REALLY in there before I order new ones. Hopefully they're clearly stamped. I'll also need to see what (if any) bearing seals are used and order fresh ones. I guess that's my project for tomorrow (busy finishing something else today).

Greg
 
Ischgl99 said:
Those letters are usually manufacturer specific and could have a different meaning from one brand to another. If you have a part number 30209A or 30209B, for example, that usually means there was a design change to the bearing. The important dimensions will still be the same, so it would be interchangeable with any other 30209 bearing, but the A design would be retired and anything new would be the B design. A different manufacturer might not have made any changes yet for their bearings, so it’s not that important between brands.

This document shows what Timken uses for their bearings:

Click to expand...
Thanks. I'd found a similar Timken bearing nomenclature publication, but it didn't say anything about A/B/C suffixes. But now that I'm looking again, I realize that the suffixed ones that I saw earlier (on Amazon) were for National and NSK bearings. So it makes sense that these may just be their "revision numbers" -- and I'd likely want to go with the highest letter if ordering.
 
woodchucker said:
So C1 C2 c3 or the clearances for the bearing so a C1 is super tight, a C2 is a tight fitting. I use that on my travel on my table milling table. A c3 is a looser fitting. Usually a general fitting these days. If I remember correctly, CN is a normal but c3 is becoming the de facto standard in a lot of applications. It allows for heat not as precise
Click to expand...
Ya, I've read that we don't want tight tolerances here, to allow for the spindle diameter swelling with heat. And also, that the drive side needs to be a slip fit to allow for tightening the spindle nuts to remove end play (but not TOO tight).

Again, I'd better tear mine apart to see what's being used before ordering. Will do that soon.

Thanks again everyone.
 
gregreid said:
Ya, I've read that we don't want tight tolerances here, to allow for the spindle diameter swelling with heat. And also, that the drive side needs to be a slip fit to allow for tightening the spindle nuts to remove end play (but not TOO tight).

Again, I'd better tear mine apart to see what's being used before ordering. Will do that soon.

Thanks again everyone.
Click to expand...
He is talking about internal clearance between the rolling elements and races, that doesn’t apply to tapered roller or angular contact bearings. Once you preload the bearings, there is no more clearance. The tolerance you are talking about is determined by the spindle dimensions, not the bearings. For a tight fit, the OD of the spindle at that bearing location would be on the plus side, for the slip fit, on the negative side of the nominal bore size. The bearings themselves will be identical (assuming the same size bearings are used).
 
gregreid said:
Thanks. I'd found a similar Timken bearing nomenclature publication, but it didn't say anything about A/B/C suffixes. But now that I'm looking again, I realize that the suffixed ones that I saw earlier (on Amazon) were for National and NSK bearings. So it makes sense that these may just be their "revision numbers" -- and I'd likely want to go with the highest letter if ordering.
Click to expand...
The revisions are meaningless between brands, and might not even be the same changes, so you don’t want to base your purchasing decision on that. The revisions could have been made decades ago, so you won’t have a choice of which revision to order if buying new. If someone is selling new old stock on Ebay, it’s possible to find older designs available. In the case of Timken, I believe the A revision was mostly adjusting the tolerances to meet current ABEC and ISO specifications since many of their bearings were first made before a lot of the specifications were standard. Another brand could have started making those sizes to the current tolerance classes and would not need to revise the design and would appear as an “older” design compared to a different manufacturer.
 
Personally, I'd measure the spindle run-out before doing anything. It's possible, it's ok. To do that use a dial test indicator inside the spindle taper. I understand wanting to improve things, but to do so, you need to know where you started from.
 
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