Understanding Bearing Tolerance: Diameter 55 k5

[Andreii]

Hi All

On the following picture http://img.photobucket.com/albums/v309/Andreii/ujj.jpg" , I have the tolerance Diameter 55 k5. Of course there is a big difference between k5 and K5 but that has nothing to do with my post. I would like to know why is exsactly this tolerance there? Why not, for example, Diameter 55 s3 or Diameter 55 j2 or Diameter 55 k4 and so on, why exsactly k5?

So far I have got part of an answer but it does not help me. It might be because of this:
http://www.skf.com/images/cat/images/1/1_0/017_0212.jpg
The most lowest part of k5's red color is on the exact location from the 0 Line comparing to my piece of drawing but that makes no sense to me. There (on the SKF picture) are no Diameters given to ''read'' this k5. How can I see this, so microscopical small, length (between k5 and 0 Line) is correct comparing to the drawing?

Tried to help myself with tables here:
http://www.skf.com/portal/skf/home/products?lang=en&maincatalogue=1&newlink=1_0_76

but nothing so far...


Along this, I would also like to ask two other subjects:

http://img.photobucket.com/albums/v309/Andreii/trrr.jpg" ?

Also, why are some of Ra's http://img.photobucket.com/albums/v309/Andreii/raji.jpg" on the separated part of the drawing (in the top right corner) - some of them are also in brackets, why?

Hopefully we could figure that out.

Thank you for the reply.

 

[FredGarvin]

In typical applications, the shaft OD size and tolerance is usually stated by the bearing manufacturer. It takes into account desired press, ball radial clearances, inner race stresses and a few other things. Most manufacturers have done quite a bit of work to model their bearings and to ensure their stated life expectancies. Bearing fir is the number one control over the health of the bearing.

As far as the Tr40x3 call out...I have no clue, especially without knowing what the entire print looks like. As a guess, it looks like 40 mm diameter by 3 mm deep. I can not agree with the thread idea especially since it is being called out as the primary GD&T datum. If a thread is called out as a datum one usually references the pitch diameter for the datum diameter.

As far as the surface call outs...that's just weird. It doesn't make any sense. Usually you will see a note saying this is the desired surface roughness unless otherwise specified.

 

[Ranger Mike]

HAving been product manager for a company that made surface texture measurement instruments, the call out is not to ANSI B46 specs...see attached
when only one call out is on top of the check mark symbol it says the Ra should not exceed this amount...any call out inside the Divisor sign is the cut off length or assessment length

 

[Andreii]

Fred about tolerance on the shaft; I have to prove it why is, on the drawing, used exsactly this tolerance. I know the bearing fit in this example but doesn't say much to me why the tolerance is this. I have known what you typed and tried to say it to the professor on university but he rejected it. Also I have a book where is visible in which situation, on which fit and on which element (in this case bearing) is exact tolerance given. I described this too but also this has been rejected. I need to prove why this tolerance is used and need to relay on engineering standards. Thats why I mentoined the picture from SKF website but this is only 20% of the answer. Everything what says to me on the picture is the final solution, which is k5. But need the diameter given in some table to see why is the length (if i understand correctly) from 0 Line to the most lowest part of k5's red color, exsactly 50 (mm). Does exsist the table similar to:

Diameter Of Shaft ||||| Fit ||||| Tolerance

... - 50 ... k5

I cannot (tried it) just say ''The tolerance is because manufacturers suggest so the element will have as long life expectancies as possible''. I need to relay on the standards, tables, pictures to give a reason why is chosen exsactly k5. So I am still trying to figure out why is this ''length'' on the picture 50mm. On the bearing shows very well where is 0 but nowhere is some kind of Diameter Scale.

About the Tr. The picture of the main 3D model is http://img.photobucket.com/albums/v309/Andreii/Slika9.jpg . I think the Tr belongs to thread, the specific kind of thread which is showed in my first post. At least this is what my research showed. I just wanted to make sure its correct.

Ranger Mike did you relay, in your reply, on the Ra's that are located in the right top corner of the drawing (its part is showed in my first post)? Because from your reply and file that you attached I think we didn't understand each other. You were trying to say what each symbol for roughness means. I already know this, was just interested to know why are some of them separated and why are some of separated ones inside the brackets. It might be logical, as Fred said, if, on specific surface, isn't the symbol for roughness given then it means the symbol(s) in the top right corner is/are valid but why are some of them in brackets then?

 

[Ranger Mike]

got no idea..the dude who tolerance them was not following conventional method...but Ford Motor Co didn't either...if it works for your company internal manufacturing ,,,then its good enuff i guess

 

[FredGarvin]

Fred about tolerance on the shaft; I have to prove it why is, on the drawing, used exsactly this tolerance. I know the bearing fit in this example but doesn't say much to me why the tolerance is this. I have known what you typed and tried to say it to the professor on university but he rejected it. Also I have a book where is visible in which situation, on which fit and on which element (in this case bearing) is exact tolerance given. I described this too but also this has been rejected. I need to prove why this tolerance is used and need to relay on engineering standards. Thats why I mentoined the picture from SKF website but this is only 20% of the answer. Everything what says to me on the picture is the final solution, which is k5. But need the diameter given in some table to see why is the length (if i understand correctly) from 0 Line to the most lowest part of k5's red color, exsactly 50 (mm). Does exsist the table similar to:

Diameter Of Shaft ||||| Fit ||||| Tolerance

... - 50 ... k5

I cannot (tried it) just say ''The tolerance is because manufacturers suggest so the element will have as long life expectancies as possible''. I need to relay on the standards, tables, pictures to give a reason why is chosen exsactly k5. So I am still trying to figure out why is this ''length'' on the picture 50mm. On the bearing shows very well where is 0 but nowhere is some kind of Diameter Scale.

About the Tr. The picture of the main 3D model is http://img.photobucket.com/albums/v309/Andreii/Slika9.jpg . I think the Tr belongs to thread, the specific kind of thread which is showed in my first post. At least this is what my research showed. I just wanted to make sure its correct.

Well, I guess you are going to have to be able to pull a bunch of numbers out of your butt, because, like I said, there are a lot of things that go into a bearing fit. You're going to have to look at the things I told you earlier like radial clearance in the bearing, lubrication paths, shaft speed vs. inner race fit and expected increased in OD...There's a lot going on there.

As far as the drawing, I honestly do not know. I don't work in the European type of drawings (which this appears to be) but IMO it is a horrible drawing.

Good luck.

 

[Andreii]

Ok I was able to help myself and figure it out.

To share with others what I learned:

About the tolerance: I searched something like http://img.photobucket.com/albums/v309/Andreii/Slika9-1.jpg . Now this helped me determinating the exact tolerance.

Fred (and others) if you would like to save it, I suggest you to do so because you might need it later - the table is really helpful. I haven't written it myself. I could find it before on SKF but there are thousands of different tables. Just a suggestion :)

About the ''Tr'' - It was the kind of thread which I showed so I presumed correctly. In USA probably engineers named it somehow else.

About the Ra's in the top right corner: Same as you said Fred. The one before the bracket means that roughness is for the surfaces where aren't other ones stated. The ones in brackets don't have a special meaning but only as a collection of different roughness that are already stated on the drawing.