Torque values?

[reubj]

As a free lance mechanical designer I often specify torque values for machine screws for assembly drawings. More often than not the customer questions my use of "lbs-in" as a torque value. They insist on "in-lbs". I usually change the drawing to "keep the customer happy" but is this the right thing to do? Thanks for the feedback

 

[TheTick]

Mathematically, there is no difference, since the notation symbolizes the results of multiplication.

I rarely see lb-in; almost always in-lb.

"Great ideas need landing gear as well as wings."--C. D. Jackson

http://www.EsoxRepublic.com

 

[Bgoldstein]

I'm certainly not an expert on this, but I've always seen english torque values expressed in "distance"-"force", such as in-lbs and foot-lbs. Of course, metric seems to be the exact opposition of this, with N-m.

 

[MintJulep]

IFI "Inch Fastener Standards" book consistantly uses "lb. in"

Torque is defined as a a force applied at a distance, which is consistent with pound-inch.

I bet your customers would never ask to change Newton-meters to meter-Newtons.

 

[CoryPad]

reubj,

Inch-pounds is the standard way in US industry to present torque values. There is no particular standard or guideline that covers this subject, as far as I know. One pound times one inch (or one pound-inch) is equal to one inch times one pound (or one inch-pound), so it isn't a question of wrong answer but presentation preference. This is one of the problems that occurs with the Inch-Pound system used in the US - there are no standards that cover abbreviations, etc. I have read that some people like to differentiate rotational energy (pound-inch, pound-feet, etc.) and static torque (inch-pound). Because of the info above, and many more reasons, I recommend the conversion to and use of SI units.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[CoryPad]

I wrote my previous response while TheTick, Bgoldstein, and MintJulep posted theirs. I was surprised to see that IFI uses pound-inch - that is not used commonly by the fastener industry (manufacturers, users).

One small correction regarding SI units - you shouldn't use a dash to separate units. Rather, use a space or a dot: e.g., N m or N&[ignore]middot[/ignore];m.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[aviat]

From machinery's handbook:
Torque or moment is commonly expressed in pound-feet, pound-inches, kilogram-meters, etc. Metric (SI)is newton-meters.
Work is force times distance and is expressed in foot-pounds, inch-pounds, meter-kilograms etc. SI metric is the Joule.

Because there are two systems using the same units, to differentiate it is common to show torque as lb-in as you do.

 

[TheTick]

stupid question, Cory....

how do you type the dot?

 

[Sparweb]

Even US mil-standards use differing notations:
Mil-Hdbk-60 uses pound-inch (Newton-mm),
Mil-B-7838 uses inch-pound.

"View-Source" on my browser reveals that you must type "_&_m_i_d_d_o_t_;_" to show a · on the screen. (I had to put the underscores in to prevent the browser from automatically converting the characters to a dot on its own)

STF

 

[unclesyd]

Num Lock on and Hold down the ALT key and type on the Numeric Keypad.

Alt 250 ·

Alt 248 ° 100°C

Alt 241 ± ±100°C

 

[CoryPad]

TheTick and SparWeb,

Please review

http://www.xcalcs.com/docs/symbolinfo.htm

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[chicopee]

Has any body asked about convention:
in-lb in Imperial units and
N-m in metric

 

[gearguru]

chicopee,
in metric units the torque is measured in N·m
The metric units suppose to correspond with the way how they were derived/calculated.
" · " means "multiplied by" while " - " means "minus".
In Imperial units I have seen any combination of in lb (lbf).

 

[Sparweb]

Most metric moment/torque values come out in kN•m, because a newton is such a small force. I remember a college assignment in which the beam was so long, and the force so small, that I deliberately wrote the units "N•km".

Very few of my classmates found it as funny as I did.

STF

 

[gearguru]

SparWeb,
both your units are acceptable. If logical, it's a different story.
In the automotive industry we use the torque in N·m, the numbers are reasonable.
By the way - the 1988 GM metric standard properly defines the N·m as a unit of torque. (The same standard always shows "lbf" as the unit for pound(force) to make the difference between the mass and force, what is the main reason why we have the Newtons in metric system...)
How did you make the dots bold?

 

[Iskit4iam]

As Uclesyd illustrates typing a code number with the alt key depressed generates a symbol in many applications.

= ia Alt 243. These are ascii codes for the symbol. To get a complete list of symbols accessible this way do a search for ascii codes and pick a table that is easy to read.

Some tables don't show the extended ascii codes (above 127)so find one that does.

 

[chicopee]

one more thing gearguru, the "-" is not a minus sign, it is a hyphen which could be used instead of the dot product for metric but then here goes the convention.

 

[CoryPad]

chicopee,

How does one know the difference between a hyphen and a subtraction sign? You can't guarantee which is which, so SI style guides state that compound units are separated with a space or a dot, not with a hyphen.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[gearguru]

chicopee,
I have have never seen "-" used in place of "·" in any metric standard. The convention youre talking about is non-metric and can lead to confusion, therefore I would not recommend it with metric units. Obviously most important is to know, what we are doing.
While in the college (in a "metric" country), when we calculated some engineering problems, at the very end we usually performed the same calculations symbolically with units, using the same formulas (sometimes very complex) just to prove that the results are valid values, making sense for the given problem.
Is there any standard allowing using "-" in place of "·"?
As I already mentioned, the GM standard uses "·"
Regards
gearguru