Torque Stick - my test.

[macabethiel]

My Torque Stick arrived yesterday so I have tried a test on the SL wheels.

Firstly I used my 17mm long socket as it has a plastic outer liner to prevent damage to the alloy wheels / paintwork being made by Sealey specifically for wheel bolts.

I had tightened all the wheel bolts to 60 lb ft using my Torque Wrench a couple of weeks ago when I fitted the wheels after having some new tyres fitted.

I attached the Torque Stick (rated at 110 Nm) to my wrench with the long (hexagon only) socket at the end.
I then held the end of the socket with my left hand so I could feel /sense movement. I then pulled the trigger with the Kielder Set in low power mode. As soon as the hammer action changed in sound I released the trigger as the socket had stopped rotating.

I then checked the bolt with my Torque wrench set at 90 Nm and it clicked, I repeated the process again at 100 Nm and it clicked then I went to 110 Nm and it clicked. I then jumped to 120 Nm and it did not click.

My conclusion is that the Torque Sticks are quick to use but probably only accurate to within 10%. I then found this video where an engineer detailed the reasons for variations in results.
My conclusion is that I will get another Torque Stick rated at 90 or 100 Nm then use my Torque Wrench for the final nip. Good news is it's reduced the effort in removing and refitting bolts - probably not worth the effort & cost if you are fit & healthy and under 60 DIY'er

https://www.youtube.com/watch?v=6ccxHCwnQPY

I have pasted the interesting post below.

Engineer here, I think I know what might be happening--sorry that this is going to be long.

First, a word about how torque sticks in general work. You'll note each stick is thinner as you go to lower torque specs. This makes each stick have less "torsional stiffness." Think of a graph with the torque on one axis and the rotation (in degrees angle) on the other. Each torque stick will have a different trace of torque vs angular displacement. The smaller ones have more angular deflection for a given amount of torque. Keep this in mind.


When you have no impact mechanism, this reduced torsional stiffness is irrelevant because the force is constantly applied. Thus, all the torque applied is passed along to the end of the torque stick. And the time associated with force application is irrelevant because it's essentially zero.



Now what happens with the impact mechanism? Starting with no or very low torque, the mechanism doesn’t actuate, you have no hammering action, just a steady/smooth. It takes a certain minimum amount of torque to cause the hammering action, which occurs when the torque (reaction torque, here) overcomes the dog/pin static torque, causing relative motion between hammer and anvil.

Since we have enough reaction torque to activate the mechanism, the tool behaves differently. Now, it delivers torque in discrete “chunks.” The torque delivered is much higher, but is short in time duration—an impulse. This is how a regular hammer works in striking a nail—the mass of the hammer and its velocity determine that energy it will be able to deliver to the nail.



But what if that carpenter’s hammer hits a nail covered with several thick layers of rubber? In this case, that impact energy is diverted into compressing the rubber instead of driving the nail. The same amount of energy is present, but less is delivered to the nail because more went into compressing the rubber matting over the nail.

The torsional stiffness of the torque sticks creates the same effect—the discrete impulse of the hammer mechanism is diverted into twisting the torque stick, causing each impulse to be changed into a longer time but lower peak event. The less stiffness, the more time and the less twist. The more stiffness, the less time and the more peak force.


That time component is absolutely key. There is a time parameter associated with each combination of torsional stiffness and impact force. The more torque or the less stiffness, the more time is consumed by each event. After each blow, some time must pass when the energy absorbed (stored) by the torque stick is returned to the system. Engineers would definite a “torsional modal frequency” to capture that time.

If the impact tool can apply another hammer blow before the torque stick has dissipated the energy it stored, then not all the energy from the torsional deflection will have been returned to the system yet; so the energy “accumulates” and the applied torque will increase. It’s as if before we had a swimming pool being filled at the same rate it was leaking out, causing the water level to remain constant, then suddenly someone plugs the pool’s leak and the water starts to rise.



Because the deep socket is less stiff in torsion than the short socket, it mimics some of the effect of the torque stick and it makes that time factor longer. This makes it more likely that energy will “pile up.” More specifically, it lowers the natural torsional resonant frequency of the system.

The shallow sockets have slightly higher torsional frequency, make the additional energy “pile up” at a much lower rate.

All that to say this: the “medium torque” cordless has much higher rate of hammer blows, and that frequency being higher than the natural torsional resonance of the system, it will allow the energy to “pile up” a bit, causing the delivered torque to the exceed the rating of the torque stick.


Torque stick manufacturers would do well to publish a maximum blows per minute “BPM” for each torque stick corresponding to its torsional modal frequency. But since they don’t know what sockets you’re using or anything, they can’t publish anything meaningful.

The takeaway here is not that the torque sticks need to be “calibrated”—it’s that they need to be used with a tool that has a low enough BPM rate to fall beneath their natural frequency.


PS: If you tried the highest torque rated sticks with the medium torque gun, you’d find this problem almost entirely disappears. WHY? The higher rated sticks are stiffer, have a higher frequency, and this frequency is almost certainly higher than the BPM rating of even the medium torque cordless gun.

[solarman216]

Ted that is brilliant, why? because I am a picture thinker, I understood all in that post, because I saw it in my mind but could never ever of found the words to describe it, Rick

[macabethiel]

Originally Posted by solarman216

Ted that is brilliant, why? because I am a picture thinker, I understood all in that post, because I saw it in my mind but could never ever of found the words to describe it, Rick

The Missus put's it differently she says I have verbal Diarrhea!

[solarman216]

No the ability to say what is happening, great Rick