Does clicking a torque wrench more than once add torque each time.

I would agree that in practice, you don't really need to overthink it: make sure you torque wrench is calibrated and in good condition, use it correctly, wait for the click (remembering additional clicks don't increase the torque if you use it correctly), and you're good to go.

But what's the point of having a discussion forum if we aren't going to discuss things? Everyone here has experience with wheels and lug nuts, just like oil, so lots of people have input and want to discuss it. Different people have different levels of experience, some anecdotal (probably mostly anecdotal lol), some experimental, some analytical, so it's good to share information and discuss.

 

It's funny how people over think things like this. I can count on one hand the times I've seen any backyard mechanic even attempt to check the accuracy of their torque wrenches (I'm stuck at 2 fingers now at 50 plus years old). But, oh goodness, that extra click...

 

How about fasteners other than lug nuts?

I have seen many of them break by over tightening with a tork wrench.

Never seen a lug nut break.

 

Lug nuts aren't special. Any fastener can fail if it's stressed beyond its yield strength.

 

Thank you for your time. Your answer showed me why I am not going find a formula and that I appreciate. I understand more than I did.

 

Well, since we’re on the subject of lubricant. Do you all reduce torque values when using loctite?

I never have, but I don’t use it much.
Mostly on hub bolts and stuff like that.

 

This technique is also used when torquing up structural steel bridge bolts. Both when running a skidmore to test bolt strength or just using the turn of the nut method.

 

No. Loctite isn't a lubricant and doesn't change the friction level enough. This is by design.

 

Unfortunately, while we don't typically think of Loctite or any other thread locking compound as "lubricant", they absolutely do change the properties of the surface interaction at the threads when applied--meaning that it will affect input torque. It's not going to have as big of an effect as slapping some moly grease on the threads, but it does have an effect.

Henkel (Loctite's parent company) has several customer-facing white papers that go pretty in-depth on the topic of fasteners, fastening systems, thread lubrication, etc. if anyone wants some further reading. It's pretty interesting.

https://dm.henkel-dam.com/is/content/henkel/LOCTITE-Threadlocker-Manual

 

You all do get that a bolt is nothing more than a spring. The applied torque is meant to place the spring into it's elastic region and achieve desired clamping force. For a typical bolted interfaces it is not rocket science, +/- 10% will be fine in all but critical operations, of which 99% are not.

 

Technically, everything is a spring if we really want to get into it.

I agree that in practice, you don't really need to think that hard about it: just use the right tool, use the tool correctly, and follow the MFR instructions/specs and you should be good to go. But that being said, the math and physics behind it all is very complex, and pretty interesting IMO.

 

But what about when you are torqueing the lug nuts while using a sloppy fitting socket and not maintaining a 90* angle between the lever and the fastener? You could be over or under depending on the angle and now your wheels might fall off.

 

Yea, the science behind it is interesting.

The bolt is more like a wedge. Unless the bolts are yield type, I do t think there’s much spring to it.

Basically, a bolt in simple form is a wedge wrapped around pin.

 

Another fun one seen fairly often at work - torque spec is 100 in/lbs and the torque wrench just clicks and the fastener doesn't move at all. Trying to explain to some people that it isn't torqued to spec of 100 in/lbs is mind blowing.

 

Nah, at that point just grab your impact and throw some ugga duggas at it and you're good.

 

You certainly make up for my habit of never torquing anything in the universal force of Even Steven.

Something else to play with is calibrating the wrench with a weight hanging 1 foot from pivot. Set to 50, hang 50# and it should click.

 

They're not hard to. I bet just about any full grown man could snap one. I know guys that really should use a torque wrench from their tendancy to overtighten everything thus ruining the lug bolts in quick order.

 

There is for sure some spring, in fact that's what creates the clamping force. You're 100% right that a bolt is really just a fancy wedge, the simplest of machines, an inclined plain. Turning the fastener forces that wedge against the wedge on the opposing part. This action induces internal stress and (and therefore strain, i.e. elongation) in the fastener. We just want to make sure that this stress and strain is in the elastic range of the material and not the plastic range--which is exactly where a torque spec and fastener size is defined by whoever is designing the system.

In fact, one of the more accurate ways of measuring clamping force is to measure the elongation of the bolt itself.

 

Trust me, I know from experience that once the bolt gets smaller, you went too far.

Seriously, if I were to guess. I probably over torqued most stuff. As do most people.

 

All those engines we built using needle torque wrenches, hardly any of them blew up. That's precision.