Dear Adrian and All,
on 2002/04/27 11.26, Adrian Jadic at [EMAIL PROTECTED] wrote in
[USMA:19685]:
I have selected portions of your post and added some remarks to support my
view that metrication gives many industries a once-in-a-millenium
opportunity to review many of their past practices.
<snip>
> ... if the standards for electric motors
> will not change to hard metric then people will always use the HP ratings
> and present ANSI mountings which are ifp based and refer to shafts as 1" and
> keys as 1/4 etc. And no matter how hard you will try you will never be able
> to rewrite the standard to say that the shaft is 2.54 diameter because
> everyone will object and even if you did change the standard they will
> reverse back to English units ...
You are quite right. Users of old units will still use the old names while
the sizes are in rounded old units.
And this practice will continue until one designer, somewhere, says,
'Hey, what if we retested the size we need for all of these shafts? What
would happen if we used a 20�mm shaft with a 5�mm key?'
All of a sudden this designer is saving his company loads of money. It is
most probable that the original designer used the 1 inch shaft with a 1/4
inch key simply because that was the nearest size available for his first
prototype. Old standards were, almost always, written for old rounded values
of inch-foot-pound units.
I am reminded here of a story about General Motors who saved so much money
by rationalising the number of parts when they changed to metric that it was
not worthwhile monitoring the 'cost of metrication' because they were making
money from the process.
<snip>
> Let's give another example:
>
> ANSI B94 is the standard for Wearing Bushings. All dimensions and tolerances
> are given in ifp. How will the engineer design a machine using metric units
> when he has to face the colossal task of converting every dimension and
> tolerance in that machine and basically redo the drawing and the specs for
> every wearing bushing or whatever part he is using. Even more the names of
> the bushings are designated as H-xx where xx is a number representing how
> many multiples of 0.0156" fit in the OD of the bushing. EX: a 0.5" dia is
> called H-32. So the ifp is also embedded in the name. If say you rewrite the
> standard in metric units. How will you call the bushings and how will you
> justify the rule you used in naming the bushings. If you just go ahead and
> just soft convert it you will be the laughing stock of every mechanic in the
> land who will say: screw those bureaucrats!
As I said earlier, opportunities like this, to rethink your operation with a
view to making quantum improvements, are extremely rare. Soft conversions
are invariably foolish and so the better process is to retain the old
standard (together with its old language) while you rethink the whole of the
operation in a rational way. This is pretty much the approach taken by
mechanical engineers in Australia; they simply run to two sets of lathes and
milling machines and two languages � old and metric. They tend not to do
conversions but work distinctly with one mindset or the other. This is a
slow process but it matches the slow process that is usual in replacing all
of the tools in a mechanical workshop.
Cheers,
Pat Naughtin
CAMS - Certified Advanced Metrication Specialist
- United States Metric Association
ASM - Accredited Speaking Member
- National Speakers Association of Australia
Member, International Federation for Professional Speakers
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