×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How did Bearings end up predominantly metric?
4

How did Bearings end up predominantly metric?

How did Bearings end up predominantly metric?

(OP)
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???

RE: How did Bearings end up predominantly metric?

Because someone was smart and on the ball (no pun intended)

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: How did Bearings end up predominantly metric?

ryandias,

SKF is Swedish. Sweden is metric.

--
JHG

RE: How did Bearings end up predominantly metric?

But many times the balls inside those bearings are fractional inch .

snort.

RE: How did Bearings end up predominantly metric?

Quote (Tmoose)

But many times the balls inside those bearings are fractional inch
That's odd...I could have sworn the BBs in my bicycle's bottom bracket were nominal 6.35mm! ponder wink

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: How did Bearings end up predominantly metric?

(OP)

Quote (kenat)

Where did you get the sizing/dimensions you designed to? Did the catalogs (or equivalent web page) not list the true dimensions as opposed to the nominal size?

I grabbed a CAD model of Mcmaster and built my jig around the CAD model of the bearing. It wasn't that the CAD model was wrong, it was just a bad selection in general.

The jig tests an electrical circuit board, and wouldn't be used very much; so I did no checks on the bearing loading, rpm, etc.

Cut corners, came back to bite...

RE: How did Bearings end up predominantly metric?

ryandias, I took a quick look on the McMaster site at a bearing of approximately the size you mention when I first replied and in the product detail section it clearly sated the size and tolerance on the bore.

While I've probably done it a few times, just grabbing the CAD model and hoping for the best aint really engineering.winky smile

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: How did Bearings end up predominantly metric?

There are lots of things out there with "inches inside". I worked in France for a couple of years, at one point I had to draw up a test fixture that needed a pipe fitting so I included a metric pipe thread. The French manufacturing engineer asked me WTF is that? I asked him what they used for pipe threads, turned out to be good old NPT. This is in France where they claim to have invented the metric system.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

RE: How did Bearings end up predominantly metric?

Most people don't realize that 1 inch is the same as 25.4 mm. How crazy is that?

Seriously, as to one system being better than the other, I would simply give this reply: 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. wink

RE: How did Bearings end up predominantly metric?

Just don't talk about putting landers on inside Mars

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"

RE: How did Bearings end up predominantly metric?

Quote (dgallup)


I worked in France for a couple of years, at one point I had to draw up a test fixture that needed a pipe fitting so I included a metric pipe thread. The French manufacturing engineer asked me WTF is that? I asked him what they used for pipe threads, turned out to be good old NPT. This is in France where they claim to have invented the metric system.

I think if you look at what passes as 'Metric Pipe Threads' you'll discover that they are simply the NPT standard with assigned metric nominal values. But when you look at a table of pipe sizes you'll see that the Metric values equal the original Imperial values, as seen in the table below, as an example:

http://www.sonicinspection.com/uploads/Size_1-10in...

Now there is a 'British Standard Pipe Thread' which is not entirely interchangeable with the NPT standard. The pipe threads are the same size, but the thread profile is different, 55° instead of 60° which is what NPT uses. This means that while you can technically thread a male NPT into a BSPT female fitting, and vice versa, the threads will not produce an interference seal as would have been the case if both threads were NPT or BSPT. The only way they can be used together is if sealant compounds are applied, which while it might work in some situations, this should generally be avoided if at all possible.

http://www.ralstoninst.com/news/story/the-differen...

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: How did Bearings end up predominantly metric?

Inches and pounds seemed to get the job done 40 years ago for these Mars landers. We (the US of A) didn't seem to encounter a problem with Mars missions until countries using the metric system got involved.

RE: How did Bearings end up predominantly metric?

"Just don't talk about putting landers on inside Mars"

Most of the landers get to the ground; it's the orbiters that seem to have problems.

TTFN
FAQ731-376: Eng-Tips.com Forum Policies
[IMG http://tinyurl.com/7ofakss]
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers


Of course I can. I can do anything. I can do absolutely anything. I'm an expert!
There is a homework forum hosted by engineering.com: http://www.engineering.com/AskForum/aff/32.aspx

RE: How did Bearings end up predominantly metric?

bearings are predominantly metric because the world is predominantly metric.

RE: How did Bearings end up predominantly metric?

How many of the predominantly metric countries of the world are using "metric" units like: kgf for force or kg/cm^2 for pressure?

RE: How did Bearings end up predominantly metric?

KENAT,

kgf and kgf/cm2 are evil metric units.

I like how Canada is listed as a metric country. We do use kph on the highway and we measure temperature in °C. Our construction industry is resolutely English (Imperial?).

--
JHG

RE: How did Bearings end up predominantly metric?

Sure, kgf is unholy and an affront to all that is good about metric however, still metric.

kg/cm^2 is definitely just a derived metric.

I miss high school & university where almost everything was base metric units with exponents. Now that's hard core metricwinky smile

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: How did Bearings end up predominantly metric?

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?

RE: How did Bearings end up predominantly metric?

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!

RE: How did Bearings end up predominantly metric?

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

RE: How did Bearings end up predominantly metric?

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.


RE: How did Bearings end up predominantly metric?

Quote (ryandias)

...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.

RE: How did Bearings end up predominantly metric?

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.

RE: How did Bearings end up predominantly metric?

Nothing relevant, just thought it was funny how far off this Professor seems to be:
http://www2.southeastern.edu/Academics/Faculty/wpa...

Quote:

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)' ?

RE: How did Bearings end up predominantly metric?

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

RE: How did Bearings end up predominantly metric?

Quote (ryandias)

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?

RE: How did Bearings end up predominantly metric?

Something smells rotten on this post by
ryandias. Sorry!

RE: How did Bearings end up predominantly metric?

Quote (tbuelna)

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.

RE: How did Bearings end up predominantly metric?

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

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

RE: How did Bearings end up predominantly metric?

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....."


RE: How did Bearings end up predominantly metric?

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 smile, pls. refer attachment.

To put someone on the moon's just nothing against making the wind blow, up there. winky smile

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

RE: How did Bearings end up predominantly metric?

Quote (tbuelna)

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.

RE: How did Bearings end up predominantly metric?

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


_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

RE: How did Bearings end up predominantly metric?

Quote (tbuelna)

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.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources