1-Visitor

Question

Units

Forum|Forum|15 years ago
September 21, 2010
34 replies
5619 views

I'm used to seeing feet, inches and pounds usedin this forum but had kind of assumed it was a legacy thing, I was quite surprised to learn that (as one of the last three countries with Burma and Liberia) the US still has imperial units as its official measurement system.

From a professional point of view it would be useful to know whether US college engineering students are taughtat all inSI units aswe're starting to see a lot more US graduates here in the UK,

Cheers, Sean

S

StephenW

23-Emerald III

Yes, When I was in school here in the US (1996-2003, Texas Tech University) we used SI units in class more than imperial units. I was also working at the time for a company building construction equipment for Caterpillar who uses SI units also.
That being said, most US students (in my opinion) still don't have a feel for SI units. Day to day life is still thought of in feet, inches, lbs and then converted if necessary. I'm one of those...I have worked at companies that use SI units for 14 yrs and still basically convert everything in my head so I get a relative feel for the size or weight or whatever.

Steve

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P

ptc-1932745

1-Visitor

I can comment that in my career (I'm now 50) we always used SI units, in
High School and College, (Ill Institute of Technology, Cleveland State
Univ., Univ. of Akron) Although I never used them in industry.

I personally would like to see us eliminate all use of imperial units
from 'professional' services such as Engineering and manufacturing,
leaving only Imperial units for some consumer goods such as food,
gasoline, building materials, etc... I think that this is happening. I
understand that in England a wooden wall stud is still called a 4x2,
even though it is not manufactured in inches. ( it's probably more
difficult to call it a 100x50, this doesn't quite roll off of the
tongue, maybe 10x5 (in cm) would be better).

My children are all being taught SI units (cm, mm, and km for length,
and kg and gm for weight) in their day to day studies in primary school.

One of the first uses I find for going to SI units is describing
mechanical components, with the concepts of fractional measurements
being the most troublesome.

For example to 'accurately' show a dimension of 3/16", the decimal value
is .1875". When modeling this in Pro-e you need all 4 decimal places,
the system does not use fractions directly. When showing the dimension
on a drawing, showing .1875 +/-.0300 is frowned upon (at my workplace)
because of all of the trailing zeros in the tolerance. I have the
option of showing the dimension as 3/16+/-1/32, but this is messy in
pro-E. I could just round up/down to 2 or three decimal places, but for
'design intent' I do really want the nominal dimension to be 3/16", not
.19".

One of our customers uses imperial units but shows all dimensions to 4
decimal places, trailing zeros be damned. They also comment that the
number of decimal places does not imply a tolerance, and explicitly show
all dimension tolerances that differ from the 'default' tolerance.

Happily this will all go by the wayside when digital product definition
becomes more mainstream.

Note that you do not have this duality of fractional vs. decimal
dimensioning in SI units. I find also that more people are willing to
use 'preferred numbers' when using decimal dimensions.

I anticipate that because a majority of machinists are taught in
imperial units, and most shops have most of their measuring tools
defined in imperial units, that they will be around for some time. Two
things can change this, CMM inspection to digital product definition
models, and the requirement to report inspection results in the native
units. (no measuring the features using imperial gages, and then
converting and reporting the result in SI units).

Christopher F. Gosnell

FPD Company

124 Hidden Valley Road

McMurray, PA 15317

L

lylebeidler

1-Visitor

I graduated from Penn State with a B.S. in Mechanical Engineering in 2000.
In my studies there, we used SI units at least half the time. It varied by
textbook & instructor. Many professors insisted on using both (sometimes in
the same problem) as they knew we would face that scenario on graduation ( a
fact which has been borne out in my professional life)

--

Lyle Beidler
MGS Inc
178 Muddy Creek Church Rd
Denver PA 17517
717-336-7528
Fax 717-336-0514
<">mailto:-> -
<">http://www.mgsincorporated.com>

P

ptc-593619

1-Visitor

Sean,

The imperial system is alive and well here in the USA. Most
professionals use it with aplomb, the SI system is as foreign as a five
legged cow. It does cause some confusion and I suspect most "American"
Engineers carry out a conversion in their heads when using the metric
system. For me, it is difficult to get used to "thous" again and I try
my best to convert any Engineers to microns though to date I have had
little success. It is all rather a moot point because if a guy/gal is of
any worth he/she will work in both systems while finding one more
comfortable.

I still can't get used to weighing too much in pounds instead of stones!

Cheers back at ya,

Richard

J

JWayman

1-Visitor

I have had problems in the past when in conversation with the US office of
our UK company, I would talk about 'mils' (meaning millimetres) and they
would talk about 'mils' (meaning milli-inches - always referred to as
'thous' in England). Huge potential for embarrassment, but fortunately, it
was always sorted out before anything was manufactured!

Talking to machinists, the good old 'thou' is still used a lot, as it is
just such a convenient unit for turning and milling - much more useful than
0.0254mm.

In UK, we have been officially SI for longer than I can remember
(literally), but my children still glibly use Feet, Inches and Stones when
describing a person's height and weight. Incidentally, I don't suppose 12
Stone means any more to a US engineer than 76kg would, despite being a valid
Imperial unit! Equally, telling me a person weighs 168 pounds is no help at
all. It's what you are used to. When I was a teenager, we used to pick
Brussels Sprouts into a Bushel Box. You don't hear much about Bushels these
days. It's a handy volume measurement, though.

For modelling, calculations, drawings, etc. I would always choose SI, though
- it is much easier that way. Particularly, I find it useful, in engineering
calculations, to strip everything on both sides of the equation back to m,
kg and s, just to make sure that the units make sense. I find it much more
difficult to do that in Imperial units.

There remains the mystery that, in England, engineers talk in millimetres
and metres, but children are taught in centimetres and metres. I am sure
there is a good reason...
Then there are all the other obscure unit systems, like the one that refers
to parts of the anatomy of a gnat in relation to a small distance.

Interesting to hear that US schools teach SI, though. We will all get to
using the same system eventually.

Cheers,
John

J

jnanesh.sajjan

1-Visitor

Well, a lot of discussion happened over this topic in other forums. And
it is a good topic to understand more about the pluses and minuses of
both the worlds of units of measurement.

1_Missed-metric-moment.pdf

S

StephenW

23-Emerald III

After sending this I realized I didn't put the most important part...I WOULD MUCH RATHER WORK IN SI UNITS. It's so much easier. This is coming from a guy who grew up using imperial units and yes I did learn a little about the metric system in grade school all the way through college. But when I actually became immersed in it in business, I realized how much easier it is to use. So many things take care of themselves in SI. AND, like someone else said, no pesky fractions to make life difficult.

Now I work in the oil industry in Houston. Wow, what a step back in the past. We still put fractions on drawings for welding.

D

dgschaefer

21-Topaz II

Back in grade school in the 70's, there was a push by politicians to
move to 'the metric system', but it seems that they pushed to hard and
fast. The older generations pushed back, I think there was some
silliness of metric not being American and whatnot, and so they backed
off and no one would touch it. Seems if we just started putting both
units on things for a while, it may take a generation, but we'll get
there.

Personally, I'm more comfortable with imperial units, but certainly
understand the benefits of metric.

Doug Schaefer

R

rreifsnyder

15-Moonstone

God, I hope we never use SI for general purpose. I'm fully conversant with SI and can and will use it when needed, but I hate the idea that they tried to force this on us beginning in the 70's as someone else pointed out. Even with all the pressure we simply won't use SI and the time has come for us to stop pushing it. I have no problem teaching it alongside the Imperial units (English units here) just as we should learn any other languages we can. We have wasted far too much effort and money trying to force this. If and when people decide that they are comfortable with it, it will change. I've always found it interesting that even the rest of the world has maintained certain things in inches, namely wheel sizes on cars. They are still in 14,15,16 inch and so on. In the early 80's Ford and Michelin tried coming out with 360mm and 395 mm wheels and tires for some of their cars. It couldn't catch on not just here but everywhere. I'm not for forcing anyone else to change to English units please don't try to force us to change ours. It's another language, that's all. We need to be conversant in both.

Rob Reifsnyder
Mechanical Design Engineer/ Pro/E Librarian
L
Mission Systems & Sensors (MS2)
497 Electronics Parkway
Liverpool, NY 13088
EP5-Quad2, Cube 281

T

tcooper

1-Visitor

Didn't NASA try using both units on a Mars mission? I believe that didn't work so well. 😉

Tim P. Cooper
LMES, Houston
ITL Facility and Mockups Design
LM1 / Rm. 666

Physical Address: Correspondence:
2625 Bay Area Blvd LM1, Mail Code: A7A
Houston, TX 77058 P.O. Box 58487
(281) 283-4372 Houston, TX 77258-8784
(281) 283-4340 (F)

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