# Convert Degrees to Foot Pounds?

• posted

Working on a Deutz Diesel engine. The instructions say to torque the bolts to 30 foot pounds then turn 45 degrees.

Can I convert the degrees to foot pounds so I can use a torque wrench to make them more exact?

Is there an abbreviation for "foot pounds"?

• posted

Do what it says. There are factors that affect torque readings. The engineers have it right, no sense second guessing them.

• posted

No -- that would be making them *less* exact.

Do you have an old school protractor? (The D-shaped thing with angles marked on it in degrees.) Use your torque wrench as instructed to tighten to 30 foot pounds, and then place the protractor to measure the angle of the wrench handle. Turn it an extra 45 degrees (1/8 of a full turn). This part is to stretch the bolt after you get it to that torque starting point. And that bolt should *never* be re-used -- you stretch it once, no more.

"Ft-Lbs" is one.

Enjoy, DoN.

• posted

Yep. It is probably easier to turn 45 degrees and stop rather than to "torque" to some specified final amount.

• posted

snipped-for-privacy@deltafarms.com (Kenn E. Thompson) wrote in news: snipped-for-privacy@posting.google.com:

They are not wanting a specific 'torque' on the bolt, they want a specific amount of bolt stretch, or yield. You torque it to 30 to get it to the initial point, then they want it stretched by x mm, which is 1/8 of the pitch. So say for a M8x1.5 this is going to be .1875 mm of stretch, after the 30 lb-ft of torque are applied. As I believe Don said, NEVER, NEVER reuse a torque+stretch bolt. They are designed to stretch ONCE. They WILL FAIL if stretched a second time. And yes, technically, it is lb-ft, not ft-lbs.

• posted

On 26 Nov 2004 17:22:42 -0800, snipped-for-privacy@deltafarms.com (Kenn E. Thompson) vaguely proposed a theory ......and in reply I say!:

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You are far better off simply doing as they say.

I was amazed when I started looking at tightening techniques. I have an industrial fastener reference from a largish nuts and bolts firm here in Oz. In it they say that "guess work" by the operator is on average 35% inaccurate and that's plus or minus!....and the torque wrench is 25% ! Turn of nut (your need) is 15%. So actually, guessing is less harmful over torque wrenches than torque wrenches over turn of nut!

Then you get down to really careful, \$\$ stuff like strain gauges, special washers that show tension etc. Lastly are Strain Gauges, which these guys say are within 1%.

• posted

3 * 4 = 4 * 3. ;^)

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

• posted

"Tim Williams" wrote: 3 * 4 = 4 * 3. ;^) ^^^^^^^^^^^^^^ That's the reciprocity law, and it applies to addition and multiplication. However, there is a HUGE difference when you are dealing with vectors. If the vectors are colinear, you get WORK, and by convention it is labelled foot-pounds. If the vectors are at right angles, you get TORQUE, and label it pound-feet. The labelling is arbitrary, but important. :-)

• posted

Doesn't every bolt stretch when you torque it down? How are these fundamentally different?

• posted

Also... Doesn't this assume that these bolts are tightened past their elastic limit? Past their UTS?

Surely not...

== Jeff R.

• posted

Brain fart. I meant "Yield Stress"

(oops)

• posted

"Jeff R." wrote in news:41a88302\$0\$20863\$ snipped-for-privacy@news.optusnet.com.au:

The tightening technique is to get the bolt very near the yield point, and not over it. However, if you reuse the bolt, you will exceed the yeld point. This will result in insufficient clamping pressure for the joint, and could (very likely, actually) result in broken fastners.

The torque technique is becoming industry standard nowadays, and that is because it is inherintly more accurate. If you torque a bolt to 70-80 lb-ft, the inaccuracies of the measurement grow expotentially as you increase torque due to friction, head galling, lubrication distribution and other variables during the tightening. By keeping the measured torque lower, you reduce these inaccuracies substantially. By specifying the angle of final placement from a lower given torque, you use the thread pitch to determine the linear stretch amount for the fastener.

• posted

I'm well aware of the dot vs. cross product, but didn't know the order of the units mattered at all... interesting!

Now if only I would remember that bit of trivia. ;-p

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

• posted

Mathematically they don't matter -- and if you depend on convention then you'll just get screwed up by the person who's document you're reading who didn't know the convention.

Best to understand what you're looking at, and assume that the manufacturer _probably_ knew what they were talking about.

• posted

Precisely!! Ken.

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The Eleventh Commandant: THOU SHALT NOT ASSUME! Regards. Ken.

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"Tim Wescott" wrote: (clip)if you depend on convention then you'll just get screwed up by the person who's document you're reading who didn't know the convention.(clip) ^^^^^^^^^^^^^^ I would certainly not adhere to the convention if the context indicated otherwise. I was responding to Tim Williams post, and it turns out that he knew this as well. So..."Never mind."

• posted

On Sat, 27 Nov 2004 14:05:24 GMT, Anthony vaguely proposed a theory ......and in reply I say!:

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AFAICS, you shouldn't exceed the yield point if you use the bolt again. The whole idea of Yield point (and I am prepared to learn another lack in my "knowledge base here, believe me" is that it's the point at which the steel deforms permanently. Any bolt tightened to below the yield will return to its former length. (???)

I can see two possible problems. Metal fatigue if the bolt is in place for an extended time, and / oe under heat/cold/ vibration etc. Accidental overtightening. Thsi would be an enginerring tning. If the bolts were _really_ taken to near yield, there would little margin for error. But once a bolt has exceeded yield, it starts to lose tension anyway. That woud be dangerous.

• posted

On Sun, 28 Nov 2004 00:37:05 +1100, "Jeff R." vaguely proposed a theory ......and in reply I say!:

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AFACUI, the answer is still no if you are asking about stretching. A spring is the most dramatic example of a metal that can be "stretched" without exceeding yield stress. To stretch steel you need to apply stress. It will start to stretch under very small stress. It will _permanently_ stretch when it passes yield.

• posted

On 26 Nov 2004 21:54:28 -0500, snipped-for-privacy@d-and-d.com (DoN. Nichols) vaguely proposed a theory ......and in reply I say!:

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Ok. Why should yopu not re-use the bolt? You are only stretching it, but not to Yield.

I have questioned Anthony about this. My theory says I am right, but you guys know your stuff. So fact is against me. I am never willing to let being thought a fool stop me from opening my mouth. I have leraned a lot that way...

...everything except when to keep my mouth shut!

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