Torque Wrench use: converting foot pounds to inch pounds

[jmickelct]

Howdy,

 

Ok heres my stupid question for the day.

 

Bout to launch into a timing belt (plus) job on a 1996 OBW 2.5 EJ25 DOHC. Pretty much have my parts and accessories lined up and have a question about the loaner (OEM brand, click type, foot pound) torque wrench that AutoZone was kind enough to lend me (for a $90 deposit!).

 

I see that I will be needing to reinstall some bolts to foot pounds and others to inch pounds. Can I just be dividing foot pounds by 12 to get inch pounds? Or will I (should I) need to lay my hands on an inch pounds unit too?

 

John

[Moodybluesr]

1lb-ft. = 12 lb-in.

 

That said most applications that give you a reading in lb-in. are low enough that a wrench reading lb-ft. is not going to go low enough to give you an accurate reading. My generic 3/8in torque wrench only goes down to 10ft-lb. which means it would only be accurate(ish) above 120in-lb.

[Manarius]

1 ft         12 in            12 in-----  ----> ------   ---->   -----------1 lb         1 ft              1 lb

 

A little bit of unit conversion for you

 

1 ft/lb = 12in/lb

[mikeshoup]

1 ft      12 in                      12 in-----  ----> ------   ---->   -----------1 lb                             1 ft                                         1 lb

 

A little bit of unit conversion for you

 

1 ft/lb = 12in/lb

 

Sorry for a bit... future math teacher, and I wanna use some of that physics I've learned in college:

 

Actually, your unit conversion is wrong. Torque is a cross product of Force X Distance, or the vector multiplication of the moment of Inertia * Angular Accelration.

 

As such, the units are Force * Distance. So, the correct unit conversion should be:

 

1 (ft*lb) * 12in/1ft = 12in*lb

 

Pretty simple. But yes, essentialy multiple by 12 to go from feet to inches.

[Manarius]

Sorry for a bit... future math teacher, and I wanna use some of that physics I've learned in college:

 

Actually, your unit conversion is wrong. Torque is a cross product of Force X Distance, or the vector multiplication of the moment of Inertia * Angular Accelration.

 

As such, the units are Force * Distance. So, the correct unit conversion should be:

 

1 (ft*lb) * 12in/1ft = 12in*lb

 

Pretty simple. But yes, essentialy multiple by 12 to go from feet to inches.

Blah, future math teacher as well. I'll give you that torque isn't a quotient derived unit.

 

I hated unit conversion for a reason.

 

[/hijack]

[nipper]

EWWWW no one told me there would be math teachers here...

 

thats it im leaving

 

 

 

(hehehehehe)

 

nipper

[Smpol19]

wow, that was the first time browsing this foum has made my head hurt so much....

[uncoolperson]

that there engineering school was good for something... (geez I hope i remembered this right)

[dmanaenk]

Here's A+ question then - convert ft-lb to N-m and back to ft-lb but on Mars

[nipper]

Here's A+ question then - convert ft-lb to N-m and back to ft-lb but on Mars

 

It's really very simple. Divide 1 lb by the surface value of gravity of the earth (32.174 ft/sec^2) to get mass in slugs. Then multiply mass in slugs by surface value of gravity of any other body of consideration (such as Mars) to know the weight there. And of course, it works the other way around too.

 

For your specific question, divide 1 lb by Mars surface gravity and multiply by Earth surface gravity

 

nipper aka mad sciencetest

[mikeshoup]

Here's A+ question then - convert ft-lb to N-m and back to ft-lb but on Mars

Simple, a pound of force on earth is till the same as a pound of force on Mars. Though your weight changes, but that's because Mars is pulling on your less force.

 

Weight is a similar way of saying Force.

[dmanaenk]

Seems like someone did not make it to A+

[mikeshoup]

Seems like someone did not make it to A+

Who you talkin bout willis? (Btw, I did get an A in physics I. Physics II freaking sucks though)

[NorthWet]

Simple, a pound of force on earth is till the same as a pound of force on Mars. Though your weight changes, but that's because Mars is pulling on your less force.

 

Weight is a similar way of saying Force.

Ahhh, not true, Grasshopper! Weight (measured here in lbs) is a property of mass that is subjected to a gravitational field; or if you are more Einsteinian, a mass subjected to warping of space-time by a nearby mass. Thus, an object would have less weight (measure less poundage) on Mars, but would have the same mass. Now, an interesting thought here is that torque wrench calibration/markings are only meaningful at earth's sealevel; they should really be calibrated in something space-time-warpage independant, but I am too tired to think this one through.

 

I was impressed with Nipper bringing out "slugs". I can only think of 1 or 2 acquaintences that could trot-out the English unit for mass. Well done!!!

[forester2002s]

Aside from 'slugs' and the various ruminations about force, mass, weight and gravity, the thing to remember is this:

 

If you are only talking (torquing?) about a few inch-lbs, then be CAREFUL not to overdo the tightening; it will be very easy to SHEAR OFF the bolt if you're not careful.

 

10 inch-lbs is not very much. Sneeze suddenly, and you're in trouble!

[dmanaenk]

Who you talkin bout willis? (Btw, I did get an A in physics I. Physics II freaking sucks though)

I'm actually with you on this

Pound-force is defined as force exerted by mass of one pound in a place where free-fall gravity acceleration is 32.174 ft/sec^2. So lbf as a unit of force is unchanged, and one can use Torque wrench in lbf-s, if one ever happens to be on Mars

[NorthWet]

...If you are only talking (torquing?) about a few inch-lbs, then be CAREFUL not to overdo the tightening; it will be very easy to SHEAR OFF the bolt if you're not careful.

 

10 inch-lbs is not very much. Sneeze suddenly, and you're in trouble!

Amen! Er... I mean, GESUNDHEIT!!!

[otis]

Ahhh, not true, Grasshopper! Weight (measured here in lbs) is a property of mass that is subjected to a gravitational field; or if you are more Einsteinian, a mass subjected to warping of space-time by a nearby mass. Thus, an object would have less weight (measure less poundage) on Mars, but would have the same mass. Now, an interesting thought here is that torque wrench calibration/markings are only meaningful at earth's sealevel; they should really be calibrated in something space-time-warpage independant, but I am too tired to think this one through.

 

I was impressed with Nipper bringing out "slugs". I can only think of 1 or 2 acquaintences that could trot-out the English unit for mass. Well done!!!

Physics may not be my specialty, but I gotta add a vote for 1 ft-lb = 1 ft-lb regardless of what planet you're on.

 

I get that the same mass will have 2 different weights on 2 different planets- but we're talking about a measurement related to force- 1 lb of force on earth is still 1 lb of force on mars. so if you torque down 2 different bolts to the same spec on each planet, they will be the same.

 

NOW- if you torque your bolts by standing on a wrench (ie changing a flat tire on the side of the road), then yes, you will be applying 2 different torques depending on your altitude or planet. but if you torque your bolt by listening for the "click" of your torque wrench- then you will have the exact same torque no matter what planet youre on.

[mikeshoup]

A pound of force is the same regardless where you are. Just as a newton of force is the same regardless where you are. Just like mass is the same wherever you are.

 

What changes is the force due to gravity, aka weight.

[OB99W]

[...] but if you torque your bolt by listening for the "click" of your torque wrench- then you will have the exact same torque no matter what planet youre on.

If you "feel" the "click", yes. However, given that sound transmission requires atmosphere (or some other conductive medium), and planetary atmosphere varies greatly (Mars' is very thin, others may have none at all), that bolt might get severely overtorqued if you're depending on hearing the click. Perhaps if there's enough light, a bending-beam torque wrench might be the better choice.

[nipper]

Ahhh, not true, Grasshopper! Weight (measured here in lbs) is a property of mass that is subjected to a gravitational field; or if you are more Einsteinian, a mass subjected to warping of space-time by a nearby mass. Thus, an object would have less weight (measure less poundage) on Mars, but would have the same mass. Now, an interesting thought here is that torque wrench calibration/markings are only meaningful at earth's sealevel; they should really be calibrated in something space-time-warpage independant, but I am too tired to think this one through.

 

I was impressed with Nipper bringing out "slugs". I can only think of 1 or 2 acquaintences that could trot-out the English unit for mass. Well done!!!

 

i may hate math, but i am an engineer

 

get yourself an inch/lb torque wrench also. i cant help much with this one as my arm is calibrated after pulling a wrench since i was 5 (god that will be forty years this 29th... eeeekkk)

 

nipper

[porcupine73]

has everyone on this board gone stark raving mad??? The last time I heard 'slugs' was when my nephew spotted a big slug next to a little slug in the garden and said 'that momma slug has cute baby slugs'.

 

Anyway can't memba if I said it in this thread already but Sears has 3/8" inch pound (force) clicker wrenches on sale for 54.99 I think. Harbor Freight I think also has clicker 1/4" wrenches for like $20.

[nipper]

http://en.wikipedia.org/wiki/Force

 

damn i love mechanical engineering....... too bad its all outsourced now.

 

heheheh

[NorthWet]

...Anyway can't memba if I said it in this thread already but Sears has 3/8" inch pound (force) clicker wrenches on sale for 54.99 I think. Harbor Freight I think also has clicker 1/4" wrenches for like $20.

Again, the problem with click-type torque wrenches is that they do not work well at low torque values.. like 10ft-lbs or less. A torsion-beam 1/4" is about the only way to go.

[porcupine73]

I've been trying to find an inch-pound beam style torque wrench, but haven't been able to find one yet....do you have any leads NorthWet? If so I'm all game! The inch-lb(f) clicker I have claims to be within 4% I think when above 20% of range, which I think is 200 in-lb(f). Darn now after every pound indication on this thread you have to put (f) or (m).