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I'm wondering if there is any benefit behind double-clicking when using a mechanical torque wrench. Could it be that some folks do it to compensate for slack in the ratcheting mechanism?
In other words, would I lose anything if I torqued down with just a single click?
This YouTube video demonstrates what I mean.
Double checking your torque is never a bad thing. The only thing you lose is a half second of your time. Peace of mind is what it's all about.
One of the reasons for doing this, though, might be when you are torquing, the fastener itself becomes slightly bound up, not giving a perfectly correct reading. By double clicking, you are allowing the fastener to rest for a second, then you are back at it to get the proper amount of torque there. This is the only other reason besides habit I can tell you why someone would do this. I almost always double check my torque, but usually only when I'm doing something in a sequence. I hardly ever double click while I'm applying torque unless there is only a single fastener involved. It doesn't mean either method is wrong or right, just that people have different ways of doing things.
Of note, remember that when torquing with a click type torque wrench, you can easily over torque your fastener by doing things too fast. You can go by the torque setting of a click type torque wrench without even thinking about. Slow, methodical movements are what you want to achieve. You want to be just on the verge of stopping the twisting motion at a moments (clicks) notice. Too often while at a tire shop (Merchants, NTB, whatever), I'll see the guys rocking the car to assist (well what they think is assisting) in the torque process, which will actually over torque a lug nut without too much issue. The only time I'm sure they are giving it the right torque is when I see them using a torque stick, which provides only one set torque value. These tools give way when the proper torque is achieved, insuring you cannot over torque. I will most often loosen and retorque my lug nuts after I get home just to ensure it was done correctly ... at which point I find that most of them are torqued all over the place, only proving my point.
I spent 25 years as a Helicopter technician, and from year one i was Ordered NEVER EVER to double click a torque wrench. This double clicking that i see mechanics do drives me nuts. You are "overtorquing" if you do it twice.
It seems clear that there are two differing opinions on "double Clicking" the torque wrench. Just to qualify my experience. For a number of years, I traveled nationally and internationally to install, service and repair high end measuring systems. Calibrating the system was the most critical part of the service. During those adjustments. The use of a torque wrench was very specific to reach the correct settings to ensure machine accuracy. It was not unusual to torque, loosen and re-torque nuts and bolts many time in an effort to reach the correct adjustment when calibrating to the millionth of an inch. It was not uncommon to "double click" an adjustment to ensure the correct torque value. Torque is a measurement of force against resistance. This does not reflect movement. Torque is the effort needed to reach a specific value of force against resistance. If you chose to "double click" your wrench. What is important, is to note any movement in degrees of rotation. Some of this practices get foggy when a manufacturer uses "degrees" in their final settings. The installation of head bolts for example. New engines with aluminum blocks have specific torque values with the final adjustment done in a matter of degrees of rotation of the fastener. If the original torque value is over. That error will be magnified after tightening the fastener to an additional number of degrees of rotation. These final adjustments actually "stretch" the bolt. Allowing them to only be torqued to value one time. So if your original torque wrench value is over. In the end the bolt will have been stretched too far and be compromised. I say it really depends on the application if in question. Don't double click. I personally, like to torque in stages. Try to be more methodical. This will help with any anxiety over the need to double click.
It depends on what you're torquing and the requirements that need to be met for the item your are torquing. In the aviation industry everything is very fine tolerances and small torque ranges. A double click is over-torquing. In the general automotive industry where things are not as precise as aviation a double click isn't going to hurt anything.
I find double clicking useful.
My reasoning for using it is that when you quickly tighten the bolt or nut with the torque wrench, part of the torque goes to acceleration and only part of it increases the fastener torque. So it will be undertorqued by a very small margin.
However, the next time it's already very close to the indicated torque, so the acceleration required to reach the click will be significantly less. Thus, the next time nearly 100% of the torque goes to increasing the fastener torque.
I don't know how big the effect is -- do you undertorque by 1%, 0.1% or 0.01% the first time, but doing a second click with the fastener very near the indicated torque just feels like the right thing to do.
Of course you could have reached the same effect by doing the first torquing run very slowly so that acceleration effects are small. However, it's much faster to do the first torquing run very quickly and then do the second click.
If you know how to use the tool properly, double clicking or checking the torque a hundred times doesn't matter due to no further rotation of the fastener is performed. If the correct torque is achieved on first pass, the tool will release on every recheck after that which will not change or add additional torque. It all comes down to proper tool use. PERIOD!!!
