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???

 

[Artisi]

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.)

 

[drawoh]

ryandias,

SKF is Swedish. Sweden is metric.

--
JHG

 

[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?

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[Tmoose]

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

snort.

 

[GregLocock]

Ever been to a bearing factory? magic stuff.

Cheers

Greg Locock


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[Lou Scannon]

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!

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[ryandias]

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...

 

[KENAT]

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.;-)

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[dgallup]

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.

 

[tbuelna]

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.

 

[itdepends]

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"

 

[JohnRBaker]

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_1-10inch.pdf

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-difference-between-npt-bspp-and-bspt-seals/

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.

 

[tbuelna]

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.

 

[IRstuff]

"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
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[dvd]

bearings are predominantly metric because the world is predominantly metric.

 

[spciesla]

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

 

[KENAT]

They are derived metric units, what's your point?

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[drawoh]

KENAT,

kgf and kgf/cm[sup]2[/sup] 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

 

[KENAT]

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 metric;-)

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