Torque... We've been wrong all these years! 11

[kthree]

For many years we've rated our gear reducers in 'inch pounds'. Lately I've been noticing, mostly automotive and implement ads, torque being rated in 'pound inches' or 'pound feet'. Today I grabbed my Machinery's Handbook and there it is, "...pound-feet, pound-inches, kilogram-meters, etc." Wow, We've been wrong all these years!

 

[metalonis]

To stretch the topic a bit, the units are actually a product of force times distance (or distance times force if you like). Therefore they would more properly be displayed as a product, e.g., ft•lb or lb•ft rather than either ft-lb (feet minus pounds) or ft/lb (feet divided by pounds).

 

[drawoh]

metalonis,

ft/lb obviously is wrong. I use ft.lb. That middle dot comes from a mathematical font that may or may not be implemented on my computer, and that may or may not be implemented on the computer of whoever is reading my document.

--
JHG

 

[GrandpaDave]

Duwe6(Industrial)... Were you around when NASA's Mars Climate Orbiter missed it's target in November 1999?
A failure occurred because one company worked with Newtons and the other company worked with pounds. Can't recall
but weren't there 2 space vehicles impacted?

 

[GrandpaDave]

Follow-up: 1999 was a bad year... Mars Climate Orbiter, Mars Polar Lander and Deep Space 2, Oops from 1999

 

[tbuelna]

GrandpaDave-

I have worked on numerous NASA programs over the past 25 years, including the ISS, Delta II, Delta IV, Space Shuttle, and the new SLS booster. All of the drawings, test requirements, etc. that I created used inches and pounds. For example, fastener torques were always defined in ft-lbs or in-lbs, areas were defined in in^2, pressures were defined in psig or psia, stresses were defined in lbs/in^2, etc. These programs all had a pretty good success rate. There was never a problem with how units were defined, in-lb or lb-in, since everyone involved knew what was implied.

While working on the Space Shuttle program at Rockwell, we had no problem working with Russian, Japanese, Italian, or even Canadian engineers and their engineering documents that used metric units.

 

[dicer]

If memory serves in that machinerys handbook it specifically notes that there is absolutely no difference
between ft.lbs and lbs.ft And besides common sense tells you its the same thing. Its the measure of torque with some unit of weight at the end of an arm. Isn't 100 ft lbs the same as 100 lbs ft?
Commutative property, so for example 12ft.lbs of torque.
You can either hang 12 pounds 1 foot from the center point on the arm, or you can hang 1 pound 12 feet from the center point, you get the same torque. Realistically the lever or arm has to be weightless, when hanging the weight out so far. I guess we can be picky about the "s".

 

[mikekilroy]

I'm as picky about the s as I am with folks who want to call speed RPMS; neither should be done. Having spent 35 years working with torque motors, I have always used lb-in, lb-ft-s^2, same as all those who have used nm, kg-m, correctly since the beginning....

http://www.KilroyWasHere<dot>com

 

[Sparweb]

Back in university when working on assignments with classmates, I remember writing answers in "N*km" instead of the more common "kN*m" but nobody found it funny except me.


STF