How did Bearings end up predominantly metric? 4

[ryandias]

I have been working 8 years as a designer, and last week found out bearings are predominantly metric.

I designed a test jig and ordered a 0.25" bore, 1" OD bearing from Mcmaster to fit the jig. When we got the bearings they are ultra cheap garbage, with about 1mm of play. I figured I'd just reorder an SKF equivalent - and found out the great news that bearings are mostly metric.

I prefer metric anyways, but when out of my way to use an imperial bearing because I thought it would be more common.

How did bearings become predominantly metric???

 

[spciesla]

My point is that some (many) tout metric in a "holier than thou" tone and then embrace "unholy" metric units like kgf and kgf/cm^2.

How is kgf/cm^2 used for pressure a derived unit?

 

[KENAT]

You didn't say kgf/cm^2

You said kg/cm^2.

Which yes, incorrect for pressure but not for area density.

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[spciesla]

Good point KENAT.

However, I'm pretty sure that I've seen pressure gauges with units of kg/cm^2 written on them (implying kgf/cm^2). I never seen or looked for an area density gauge!

 

[Fugeguy]

If you ask a Brit how much he weighs he's likely to say about 14 and a half stones...

 

[VEBill]

Some of my high science teachers in the 1970s were still grumbling (or pretending to grumble) about the transition from 'cgs' to 'MKS', let alone "that new-fangled 'SI' nonsense". Of course these differences trickle down into all sorts of different derived units and constants.

 

[tbuelna]

...I designed a test jig and ordered a 0.25" bore, 1" OD bearing from Mcmaster to fit the jig. When we got the bearings they are ultra cheap garbage, with about 1mm of play.

I don't see how it could be possible that the inch class bearing you purchased could have a metric class amount of free-play. Something seems amiss here! Are you sure the amount of free-play wasn't actually .03937 inch rather than 1mm? Obviously, that would make more sense.

And as dvd pointed out, that inch class bearing could only have been manufactured in the US, Myanmar or Liberia, since these are the only countries still using the inch system. I checked available sources and could find no evidence that Liberia or Myanmar presently have any domestic production capacity of crappy rolling element bearings. So your bearing must have come from a US manufacturer, assuming what you stated is correct.

On the other hand, I have personally seen examples of cheap, crappy metric class rolling element bearings imported from sub-standard foreign manufacturers being passed-off as inch class bearings. So you might be the victim of bearing fraud. You should check your bearing to make sure it is a genuine 1 inch bearing instead of a fake 25.4mm bearing.

By the way, how have you managed to spend 8 years working in the US auto industry without knowing about metric bearings? The US auto industry has used the metric system for almost 2 decades now.

 

[romke]

as long as i can remember bearing manufacturers in Europe offered metric sizes and sometimes a limited selection of non-metric sizes. the balls used in the past however were usually non-metric. some types of tapered roller bearing for automotive wheel bearings were used in non-metric sizes until quite recently, even by "metric" manufacturers like Mercedes-Benz. that may be due to the fact that originally that part of the business was dominated by Timken.

although most engineering dimensioning nowadays is metric, there are more areas where non-metric sizing is still more or less alive: pipe fittings, automotive brake hosing until recently, kingpins, bellhousings. for pipe fittings and brake hoses the non-metric species had the advantage that due to the threads used sealing against fluid leaks was better because of the smaller top angle of the thread (55 vs 60 degrees). the advantage thus was not so much because of being non-metric but because of the different thread design.

 

[electricpete]

Nothing relevant, just thought it was funny how far off this Professor seems to be:

http://www2.southeastern.edu/Academics/Faculty/wparkinson/help/metric_units/

A measurement in the metric system that is represented by a rational number remains a rational number after metric unit conversion. (For example, 250 mm = 25 cm = .25 m). In contrast irrational unit systems , such as the English system, do not have the same property (For example, 250 inches = 20.8333... ft = 0.0039457... mile)

The definition of a rational number is one which can be represented by a ratio of integers. The last I checked, 3, 12 and 36,and 5280 are all integers, so any conversion amongst inches, feet, yards and miles cannot change a rational number to an irrational number.


=====================================
(2B)+(2B)' ?

 

[SomptingGuy]

My "burning bush" moment for SI was when I realised that (electrical) V x A gives the same power units as (mechanical) N x m/s. Likewise the energy units in matter/energy (E=mc^2) the same as those in mechanical (E=0.5mv^2) and thermal (dE=mCdT).

Suddenly physics became tangible and possible rather than a loose collection of things which appear proportional to each other. Like some kind of grand unification moment thatallowed engineering to be practical rather than theoretical.

Strangely and sadly, our media just don't seem to understand that an electric motor rated at 100kW isn't only "equivalent" to a petrol motor of 134 BHP. It has the same identical power and therefore ability to do work. They've not managed to make the leap of seperating physical quantities from their customary units.

Steve

 

[tbuelna]

I designed a test jig and ordered a 0.25" bore, 1" OD bearing from Mcmaster to fit the jig. When we got the bearings they are ultra cheap garbage, with about 1mm of play. I figured I'd just reorder an SKF equivalent - and found out the great news that bearings are mostly metric.

I did a quick search for .25" ID x 1.0" OD ball bearings on the SKF website, and there were no listings for this size of bearing. The McMaster-Carr website lists a single example of this size ball bearing, but it does not even meet ABEC-1 tolerance standards.

Are you sure what you stated in your OP is accurate?

 

[juergenwt]

Something smells rotten on this post by
ryandias. Sorry!

 

[zeusfaber]

There are two types of countries in the world - Those that have adopted the metric system, and those that have put men on the moon.

 

[JohnRBaker]

Where did you get the picture of that Liberian flag flying on the Moon?

John R. Baker, P.E.
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Product Engineering Software
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Digital Factory
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To an Engineer, the glass is twice as big as it needs to be.

 

[tbuelna]

Actually, that's the official 1836 flag of The Republic of Texas Naval Service. The Liberian flag only has 11 stripes. But I appreciate how confusing it can be for proponents of the metric system to count beyond 10.

Regardless, it doesn't matter since the Republic of Texas has put men on the Moon and has never officially adopted the metric system. "Houston, Tranquility Base here. The Eagle has landed....."

 

[RolMec]

Back to bearings...

SKF (disclaimer: me = No) will be happy to provide imperial size bearings, it's (@tbuelna) just that for a 1/4" ID there's no 1" OD, the 1/4" ID range ball bearings stop at 3/4" OD. Else you can have it all , pls. refer attachment.

To put someone on the moon's just nothing against making the wind blow, up there. ;-)

As for metric vs. imperial, one can take it or leave it and in the end for someone requiring a 1" shaft I do happily a drawing with 2 dimensions and rather have the business than the discussion. Metric system got a lot of standardization done in very various and vast fields of lots of different industries, so it's a better life, for some, to have fitting things, say only just for example from electrical and mechanical disciplines and then design it "here" but purchase it "There" and it works. Evidently so...
Kind regards

 

[zeusfaber]

Actually, that's the official 1836 flag of The Republic of Texas Naval Service. The Liberian flag only has 11 stripes.

Touché. "I was wondering who'd be the first to spot that."

A.

 

[JNieman]

As I sit here drinking coffee from my mug stating
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with the old trademarked (expired) logo, I can't help but grin at some of the statements

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[geesamand]

Regardless, it doesn't matter since the Republic of Texas has put men on the Moon and has never officially adopted the metric system. "Houston, Tranquility Base here. The Eagle has landed....."

The mission control center might have been in Texas, but I assure you the equipment in that photo (suit) did not come from Texas.

Anyway, to the original question I think a huge factor is that most of the machinery built in the world does not come from America. (Or Texas ) So with metric bearings there are higher quantities, more brands, and ultimately more bang for the buck. And if you're in the world of taper roller bearings, many fewer size choices which is helpful in most cases. My company does everything possible to design our machines with the most popular metric sizes to keep costs and lead times down.

If you're buying your bearing in large quantities, then it really doesn't matter.