Do tapered roller bearings have accuracy classes?

[fvdbergh]

Hi everyone,

I am in the process of replacing my mill's spindle bearings (it is an Optimium BF20), and I have been looking at the usual suspects on the topic (Hoss, Russtuff). Anyhow, I am pretty much decided on just replacing the tapered roller bearings (32005) with new ones, steering well clear of the angular contact bearings.

I spent some time looking at the definition of the ABEC classes, and I noticed in particular the radial runout of a typical ABEC-5 (or ISO P5) in the size I am looking at (25 mm bore) is about 4 micron, and the face runout is a whopping 8 micron. Digging around on the web, it looks like you can buy angular contact bearings in ABEC-5 or ABEC-3 (if you want to splash out), but the tapered roller bearings did not appear to have a rating attached.

So my question: do tapered roller bearings have accuracy classes?

I can imagine that variance in the roller diameter, and surface roughness of the races could cause radial runout, but the preload is user-adjustable in a spindle application, and the tapered geometry makes it easier to ensure that the inner race is concentric with the outer race.

My thoughts are that this is very different from a deep-groove bearing, where the preload is essentially built into the bearing during manufacture. On an angular contact bearing, I can imagine that the geometry of the race could be imperfect, i.e., any error in the diameter of the race would produce radial runout, even if you do control the preload.

Am I on the right track, or am I missing something?

-Frans

 

[Kernbigo]

yes i know timken's have different class's, they are listed the opposite of angular contacts, being lets say 00 being better class than a 3

 

[Bob Korves]

The first link below says there are precision tapered roller bearings, you will need to check if they are offered in the sizes you are interested in. The second link shows bearings I would not touch with a ten foot spindle...
http://www.timken.com/pdf/5722_Precision Tapered Roller Bearings.pdf
http://blsbearing.en.made-in-china....curacy-Single-Row-Tapered-Roller-Bearing.html

 

[fvdbergh]

Thanks gents!

I found the Timken "Fafnir" brochure, which provides the details of their precision tapered roller bearings. Unfortunately my mill's spindle is a little small --- they start at a bore of 60 mm.

I see that NTN offers a "class 4" bearing T4-32005X, but I have yet to locate a local distributor.

In the meantime I have ordered a pair of SKF 32005 X/Q bearings. I will try to measure their runout before I install them.

If anyone knows of a reputable manufacturer (other than NTN) that offers precision tapered roller bearings in smaller bore sizes, please let me know!

-Frans

 

[Kernbigo]

class for are the least precision 0000 are the best

 

[fvdbergh]

class for are the least precision 0000 are the best

Agreed; that applies to bearings specified in imperial units (ANSI/ABMA and some of the ISO standards).

The NTN "class 4" metric bearing (in JIS B 1514 or ISO492) appears to be equivalent to a "class 0" in imperial (http://www.ntnglobal.com/en/products/catalog/pdf/2202E_a06.pdf), which is probably good enough for my mill.

I see that the Timken Fafnir documentation recommends class 3 or class 0 bearings for milling machines (https://www.timken.com/wp-content/uploads/2016/12/5918_Machine-Tool-Catalog.pdf, page 15).

 

[crazypj]

I may be completely wrong but generally, if IRC, the higher the load rating the 'lower' the precision rating for same size bearings. More rollers, better load rating. I forget most about bearings, haven't 'HAD to know ever but learned about them around 1976~77
The higer precision the bearings though, the better the shafts and housings have to be made, that's actually the difficult part, production machining to 3 micron tolerance (trust me, it sucks on manual machines)