NEW! Ultimate C/S Prop Wrench Anti Splat Aero

[PerfTech]

Originally Posted by erich weaver

Growing weary of this as Im sure are others, but I never read/heard Allan say that the 0.8 was only an example. The quote above from Allan's earlier post, as well as the product video, seems to say that if your torque wrench measures in ft lbs, that 0.8 is the correct multiplier. I say, (as does Walt I believe) that is not necessarily the case. Ya gotta measure the length of your torque wrench and if its not 12 inches, you better do the math or plug in the numbers to the handy calculator web site that was posted to see what value to set your wrench at when using the extension.

Do you agree Allan?

And for the record, love you man, product on order

erich

All foot lb. torque wrenches are the same regardless of handle overall length. The overall length only effects how hard you need to pull on it. on a foot lb. torque wrench the .8 multiplier is exactly and always the number. It is not rounded off and it never changes as long as the crows foot or our tool is 3" and in installed straight. If you install it on the torque wrench at 90 degrees the multiplier is 0, at a 45 degree angle it is .9. This is simple math and does not change.

[Garage Guy]

So you are saying if it is a ft-lb wrench: (12")/(12"+3") = 0.8

And if it is a newton-meter wrench: (39.37")/(39.37"+3") = 0.929

And if it is an inch-lb wrench: (1")/(1"+3") = 0.25

I don't think so!

As a bunch of folks have pointed out, your correction factor should be (wrench length in inches) / (wrench length in inches + 3"), it doesn't matter what the scale is calibrated in. A lot of torque wrenches have both metric and SAE scales for example.

Of course "wrench length" doesn't include the length of any cheater bar. It is the designed length of the wrench, from the handle pivot to the socket axis.

--Paul

[schristo@mac.com]

Originally Posted by PerfTech

All foot lb. torque wrenches are the same regardless of handle overall length. The overall length only effects how hard you need to pull on it. on a foot lb. torque wrench the .8 multiplier is exactly and always the number. It is not rounded off and it never changes as long as the crows foot or our tool is 3" and in installed straight. If you install it on the torque wrench at 90 degrees the multiplier is 0, at a 45 degree angle it is .9. This is simple math and does not change.

It is my understanding that torque wrenches are calibrated from the center of the handle and that is the lever distance to be used for accurate torque and extension calculation. Where you grip effects the amount of bending moment within the tool which is properly accounted for only at the calibration point; middle of the handle. I have never seen reference to a lever length other than from the calibration point to the ratchet head.

If two similar torque wrenches, one long and one short were both calibrated at 12" the lever calculation would be the same (or very similar), however, they are calibrated at their respective handles to generate an indicated torque at the ratchet head which impacts the internal pawl size or beam arm mechanism along with the bending of the wrench itself.

Always torque from the calibration point, the handle... never use a cheater bar to make it easier to get a torque value, at least if you hope for an accurate torque.

[L.Adamson]

Assume that a nut needs exactly a one quarter turn more(90 degrees), to hit the exact specified torque value. Let's say the torque wrench is 12" long.

Get a ten foot cheater bar, and it's still going to be just a 90 degree movement. The "push" required at the end of the ten foot bar, is much less than that at 12", but the traveled distance is much farther. Works just like a block & tackle. Whether it's 12" or ten feet, the torque value of the nut, remains the same.

[PerfTech]

Originally Posted by schristo@mac.com

It is my understanding that torque wrenches are calibrated from the center of the handle and that is the lever distance to be used for accurate torque and extension calculation. Where you grip effects the amount of bending moment within the tool which is properly accounted for only at the calibration point; middle of the handle. I have never seen reference to a lever length other than from the calibration point to the ratchet head.

If two similar torque wrenches, one long and one short were both calibrated at 12" the lever calculation would be the same (or very similar), however, they are calibrated at their respective handles to generate an indicated torque at the ratchet head which impacts the internal pawl size or beam arm mechanism along with the bending of the wrench itself.

Always torque from the calibration point, the handle... never use a cheater bar to make it easier to get a torque value, at least if you hope for an accurate torque.

The cheater bar was only stated to demonstrate a point or principal, not a suggestion. As for torque wrenches that are calibrated from the handle, the only ones that are sensitive to this are the old school bending beam type that depend on the entire beam length to flex giving the indication. That type has a pivoting handle to address this issue. None of this has anything to do with the .8 multiplier or click type, gauge pull type, flex shaft internal, twisting shaft or load cell type wrenches. If the wrench is in foot pounds the correction factor with our wrench is .8, if in inch pounds it is .8 X 12. Thanks, Allan

[schristo@mac.com]

Originally Posted by L.Adamson

Assume that a nut needs exactly a one quarter turn more(90 degrees), to hit the exact specified torque value. Let's say the torque wrench is 12" long.

Get a ten foot cheater bar, and it's still going to be just a 90 degree movement. The "push" required at the end of the ten foot bar, is much less than that at 12", but the traveled distance is much farther. Works just like a block & tackle. Whether it's 12" or ten feet, the torque value of the nut, remains the same.

The problem is with the torque measurement. With and without the cheater bar the wrench will indicate that the specified torque is reached at different physical points... The method of measurement is pretty finicky. A cheater bar will place a levered load onto the wrench itself applying both an upward force and downward force (assuming a tube shaped cheater is slipped over the wrench) which will impact the measured torque at the head. How much will depend on how deep the cheater is inserted, how much force leverage is being applied, how different the material and physical properties of the wrench and cheater are for bending...

in the end none of this likely matters much though since we are dealing with pretty broad torque ranges but don't get fooled into thinking that the torque you dial up or read is pin point accurate. CDI calls calibration less than 20% 'minor'.

Good technique with a well calibrated wrench is still likely +/- 5%. It would not surprise me to see a typical tool box torque wrench with poor technique off 30% or more. Even at that error most mid torques values that we are dealing with are pretty safe. I recall a discussion here where someone was consistently braking off AN3 bolts with their torque wrench... turned out he was using ftlbs rather than inlbs... not surprising that he was breaking bolts.



To get this thread back on track...

Great solution for prop bolts! I ordered one this morning

[erich weaver]

Originally Posted by schristo@mac.com

Wrench torque = desired bolt torque * (wrench length / total length)

For a wrench length (to the handle centerline) of 12" with a 3" extension you have (12 / 15) or .8

Originally Posted by PerfTech

That is correct, this is why the .8 multiplier. Thanks, Allan

Still cant see the logic behind how the 0.8 can be a constant, regardless of the length of the torque wrench. From the quotes above, Allan seems to acknowledge that the 0.8 value was arrived at based on a wrench length of 12 inches. It therefore stands to reason that if you use a different wrench that is NOT 12 inches long, (dont confuse the issue with cheater bars - I mean a DIFFERENT WRENCH) the multiplier will be something other than 0.8. You cant have it both ways - its either based on the wrench length or its not.

Somebody find the flaw in my logic and put this to rest. Funny how little things like this can gnaw at you late at night when you should be sleeping...

erich

[PerfTech]

I will try this one more time. Forget the length of your wrench, Forget cheater bars and everything else. If you have a torque wrench that you currently use to torque things in foot lbs. and you want to torque a bolt to 100 foot lb. you set your wrench or reed your gauge at 100. If you use our prop wrench with your torque wrench and want 100 foot lbs. you set or read your torque wrench to 80 foot lbs. You do not need to do any math or calculations of any kind. We have done that for you. Allan

[LifeofReiley]

Originally Posted by PerfTech

I will try this one more time. Forget the length of your wrench, Forget cheater bars and everything else. If you have a torque wrench that you currently use to torque things in foot lbs. and you want to torque a bolt to 100 foot lb. you set your wrench or reed your gauge at 100. If you use our prop wrench with your torque wrench and want 100 foot lbs. you set or read your torque wrench to 80 foot lbs. You do not need to do any math or calculations of any kind. We have done that for you. Allan

Allan... looks like the design has stirred up the math. I get it. Thanks for another Great Product!

[rv8guy]

The constant is the 3 inch extension. The torque is applied to it, not the nut.

Stimulating discussion