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Ball bearings

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Vic10/03/2015 00:01:19
2256 forum posts
11 photos

I noticed on a bearing factors site that many imperial ball bearings are not correctly sized but are expressed in mm and rounded up to the nearest .01 of a mm. For example 1/8" is 3.18 instead of 3.175 and 3/8" is 9.53 not 9.525 Not in every case though of course 12.7 and 6.35 were ok. Why is this though, it seems odd to manufacture bearings that are neither true imperial or a logical metric size?!

Bandersnatch10/03/2015 00:14:29
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1249 forum posts
40 photos

.01 mm is equivalent to .0004" (4 tenths of a thou). If they expressed it to the next decimal place (.001 mm) they would be tacitly saying their bearing sizes are accurate to .00004" ..... which I doubt.

What I want to know is where did all the extended-race bearings go (commonly inner race but extended outer race bearings were also available)? They used to be quite commonly available (and were arguably more useful than standard bearings) but I rarely see them nowadays. I suspect they are available but to special order which is a pity.

Bandersnatch10/03/2015 01:07:51
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1249 forum posts
40 photos

.. oh, and the really dumb thing is expressing inch bearing sizes in metric at all. If they're making inch bearings they should be listed in inches .... period.

Vic10/03/2015 09:34:36
2256 forum posts
11 photos

Agreed, why not grind it to 1/8" and express it as such?

Trevorh10/03/2015 09:58:37
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279 forum posts
79 photos

Goes back to when we were at the cross roads of changing over in Industry 1970's

it seemed easier to accept that if you compared Imperial to metric to round to the nearest size

Certainly in heavy industry and the printing industry it is just accepted that if you have 3" its the same as 75mm not 76.2 same as 1/2" is 12mm not 12.7 and 1/4" is 5mm not 6.35 and so on

Its just how industry has worked out over the years

Michael Gilligan10/03/2015 10:26:33
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14023 forum posts
609 photos
Posted by Trevorh on 10/03/2015 09:58:37:

... it is just accepted that if you have 3" its the same as 75mm not 76.2 same as 1/2" is 12mm not 12.7 and 1/4" is 5mm not 6.35 and so on

.

"Design updates" maybe ... But hopefully not for spares !!

MichaelG.

Bob Brown 110/03/2015 10:38:51
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982 forum posts
125 photos

I think you will find that they have just set the dimension in metric to 2 decimal places rather than the actual dimension in metric as some get rather long like 11/64" which is 4.365625 in metric but they will show it as 4.37.

Bob

Ketan Swali10/03/2015 10:54:13
1113 forum posts
91 photos

Vic,

I collect old bearing catalogues. Bearing manufacturers generally show measurements upto 3 decimal places if they show imperial bearings converted to metric dimensions.

Picture from 70s RHP catalogue showing correct imperial measurements:

img_1990.jpg

Similarly imperial measurements converted into metric in an old NACHI catalogue:

img_1991.jpg

I am guessing that the bearing factors web software is just rounding up to two decimal places.

Ketan at ARC.

Ketan Swali10/03/2015 11:04:35
1113 forum posts
91 photos
Posted by Bandersnatch on 10/03/2015 00:14:29:

What I want to know is where did all the extended-race bearings go (commonly inner race but extended outer race bearings were also available)? They used to be quite commonly available (and were arguably more useful than standard bearings) but I rarely see them nowadays. I suspect they are available but to special order which is a pity.

I am not quite sure what you mean. For ball bearings, if the outer race is extended, the inner race is equally extended, i.e. wide ball bearing or double row ball bearing, or angular contact double row ball bearing (not to be confused with double row self aligning ball bearing). If you mean wide/double row ball bearing, then they are still in general production.:

Japanese factories refer to them as the 5000 series, and western factories refer to them as the 4000 series. Broadly similar, pictures from the respective catalogues:

NACHI/Japan:

img_1992.jpg

SKF/Western:

img_1993.jpg

Ketan at ARC.

Nicholas Farr10/03/2015 11:17:13
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1977 forum posts
937 photos

Hi bandersnatch, are these what you are refering to, **LINK** or maybe these http://www.lutco.com/Products/Radial-Bearing/Flanged-Radial-Extended-Inner-Race-Bearing/

Regards Nick,

Edited By Nicholas Farr on 10/03/2015 11:23:00

Ketan Swali10/03/2015 11:28:48
1113 forum posts
91 photos

Hi Nick,

I am familiar with extended inner ring ball bearings as in your link, as well as the self aligning type pillow block inserts, LR track roller type, etc., but I am having difficulty picturing extended outer ring by itself for ball bearings suggested by Bandersnatch. Hence I wasn't sure what he meant by the extended outer ring.

Ketan at ARC.

Gordon W10/03/2015 11:49:52
2011 forum posts

Only time I have seen extended inner or outer ring is in special order stuff. Often was used as a surface for oil seal to run on.

Nicholas Farr10/03/2015 12:46:19
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1977 forum posts
937 photos

Hi Ketan, extended outer ring bearings are usually specials for many reasons, one example is shown on the third page of the PDF which you have to open in this **LINK**

Regards Nick.

Bazyle10/03/2015 13:25:58
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4728 forum posts
186 photos

If the dimensions are given in imperial there are a bunch of kids now in industry who just wouldn't have a clue and would end up with all manner of non-fitting parts.

Quick test in the office to the two under 25's " what is 1/8 inch in mm". not a clue. Dived for their computers to google it.

Ketan Swali10/03/2015 14:19:34
1113 forum posts
91 photos
Posted by Bazyle on 10/03/2015 13:25:58:

If the dimensions are given in imperial there are a bunch of kids now in industry who just wouldn't have a clue and would end up with all manner of non-fitting parts.

Quick test in the office to the two under 25's " what is 1/8 inch in mm". not a clue. Dived for their computers to google it.

Agreed...cant blaim them...most of the time I can only think in metric. I too am guilty of this. I end up using a calculator.

For bearings, in the old days when I used to get stuck with imperial bearing measurements or an imperial bearing number, I used to call the 'old boys' in the trade who just reeled off the bearing number over the phone from the measurements I gave them!

Bandersnatch10/03/2015 17:25:53
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1249 forum posts
40 photos
Posted by Ketan Swali on 10/03/2015 11:04:35:
Posted by Bandersnatch on 10/03/2015 00:14:29:

What I want to know is where did all the extended-race bearings go (commonly inner race but extended outer race bearings were also available)?

I am not quite sure what you mean. For ball bearings, if the outer race is extended, the inner race is equally extended,

I see several people recognise these and have addressed this before I got here today. Just to enlarge a bit, the kind of bearings I meant had the race extended by a small amount ... maybe .5 mm in your language smiley .... It was just to stop potential shorting of the inner and outer race in some situations while avoiding the use of shims or shoulders and were routine in the small mechanisms I dealt with in those days. A particular use for extended outer-races that I remember was when the bearing was installed in a blind hole. The end wall of the hole would short the bearing unless it was either stepped (shouldered) or you used an extended outer race.

Tony Pratt 110/03/2015 18:34:51
904 forum posts
3 photos
Posted by Bazyle on 10/03/2015 13:25:58:

If the dimensions are given in imperial there are a bunch of kids now in industry who just wouldn't have a clue and would end up with all manner of non-fitting parts.

Quick test in the office to the two under 25's " what is 1/8 inch in mm". not a clue. Dived for their computers to google it.

What a load of cobblers, unit of measure i.e. Metric or imperial has nothing to do with 'fitting parts' or 'non-fitting parts', it's all about interest, training & aptitude.

Tony

Ketan Swali10/03/2015 19:40:46
1113 forum posts
91 photos

Tony,

You may be right in so far as it may be a load of cobblers. As I said earlier, I too am guilty for failure to understand imperial measurements, but personally I would disagree that its just about interest, training and aptitude. It may be nothing to do with 'fitting parts' or 'non-fitting parts', as you may see it, from an engineers eye, but mistakes do happen.

Example of non-fitting of parts: I ordered dies and diestocks from one of the biggest and well known Chinese suppliers to the trade. The dies were supposed to be 20mm diameter to fit 20mm diestock.

The diestocks I received were 20mm, but the dies were 20.6375mm in diameter, so they won't fit the diestock. These are split dies, so at first I thought the die had just expanded (lack of understanding on my part perhaps) or that the factory had just used 20mm round bar which was slightly oversized. Now, having never come across imperial in my school life, I would presume that the dies were not made correctly, failing to realise that the round stock from which the die was made was 13/16". Until and unless one talks about this to a person versed in imperial measures, it is reasonably easy to make such a mistake in understanding, as I did. But then, I am not an engineer. May be that is where interest, training and aptitude....and experience could come into it, I suppose.

So please, don't be so harsh on the metric generation

Ketan at ARC

Tony Pratt 110/03/2015 20:19:16
904 forum posts
3 photos

Ketan,

I stand by what I said in response to the post by Bazyle, I am guessing it is from a, shall we say ‘mature’ gentleman who is feeling the passage of time?

I am in the same boat, educated in the imperial system but in the 70’s introduced to the metric system & completely happy working with either.

I am still in work in the aircraft industry using Imperial units but can visualise in metric if required, may I also say we have many young engineers in my office, definitely educated in the metric system but I never hear them moan about using another unit of measure.

Your story smacks of incompetence on the part of the supplier, did they not work to a drawing, if not what sizes did they work to?

Best wishes,

Tony

Ketan Swali10/03/2015 21:05:02
1113 forum posts
91 photos

Hi Tony

I don't think that the metric generation is moaning. I am just saying that there may be potential for mistakes when the metric generation has not been exposed to imperial on a daily basis.

As for the dies supplier, I am guessing that something similar happened there. It is just something we will deal with.

Thanks, Ketan.

Edited By Ketan Swali on 10/03/2015 21:08:33

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