Thread: I bought a torque wrench

Originally Posted by LRJim

Very interesting topic this has become, glad you asked the supplier about the angle. I just put a square over both the alloy nut and a steel nut, they seem slightly different the steel nut seemed to have a bit more taper but it's an old nut from the series3 so could be worn down.
My sunrasias came off a series 3 and there pretty old the nut seems to fit the taper well surprisingly. But again could be worn down.
On the subject of steel rims, I went to have my wheels balanced and the centre was too big for the machine I was really surprised they couldn't do it. Anyone else had this problem before?

Cheers Jim

The Sunnies might be different though, i did hear that somewhere many moons ago. Just dynamic are a little different. Which is why i brought it up.
In theory a 60 degree taper would have a greater surface area than a 45 degree taper where the nut bites the rim which i suspected would effect torque settings based on resistance from the mating surfaces however i may have to eat humble pie here, im not sure. Waiting on a reply actually hahaha.

Yea mate i went to a guy with my disco 33x10.5x15 and had to get a puncture fixed. They could not balance mine either as my tyres were too big so did not charge me for the fix.

Originally Posted by DAMINK

So your saying the mating surfaces dont play a part in torque? The resistance you get from the mating surfaces specifically?

Not exactly.

The type of surface plays a part as it affects the co-efficient of friction between the surfaces. For example a highly corroded surface will change the torque required to achieve the correct tension.

However the area of the surface has no effect as the friction force is dependent on the force normal to the surface, not the area it acts upon.

Where you are now adding a complication is in changing the taper angle as the friction force acts normal to the surfaces. This means that with a more acute taper angle the resisting force along the axis of the bolt is less. So for a given torque the nut will move further down the thread thus increasing the tension in the bolt. In reality though, and without doing the maths, I’d say the differences between tapers would be bugger all.

Cheers,
Jon

Originally Posted by DAMINK

True perhaps but NO ONE owns a volvo so its a non issue

You laugh, but my 740 is my Landrover Rescue vehicle.

Originally Posted by jon3950

Not exactly.

The type of surface plays a part as it affects the co-efficient of friction between the surfaces. For example a highly corroded surface will change the torque required to achieve the correct tension.

The more friction the more it will effect the torque reading IMHO.
See my thinking is simple. Lets exaggerate the situation for a second. If i have a flat nut mating to a flat surface when the nut tightens it will dig into the mating surface as well as pull on the bolt. No washers!
If you get a massive huge nut to do the exact same thing then there will be more resistance between the mating surfaces meaning in reality the bigger nut would need a higher torque to achieve the same actual result or the same amount of pull on the thread as the smaller nut with less resistance.

If this is to be true then thats been my point all along.

A 45 degree taper will have for argument sake 1.5mm of actual mating surface where as the 60 degree may have 1.8mm of actual mating surface as the angle is longer. Sure the nuts will go deeper but thats not relevant.
Whats relevant is the mating surface IF what i say above is true.

Either im not clear in what im trying to say, or im wrong flat out. Cant see how more resistance cant effect the torque settings. Still scratching my head over that.

Your first sentence is correct.

Friction, or your resistance, is simply the force applied normal (or perpendicular) to the surface multiplied by the co-efficient of friction. The area has no effect.

The torque you apply to the nut rotates it, thus moving it down the thread on the bolt. Moving it down the bolt pushes it against the mating surface. This applies a force to the surface. It doesn’t matter how big the area of the mating surfaces are, the force applied is the same. (The pressure on the surface will change because pressure equals force divided by area.)

Because the nut is turning, it is also trying to move across the surface and friction is the force resisting this movement.

If the mating surface is flat then the normal force is the full force applied. If the surface is tapered then the normal force is the applied force multiplied by the sine of the angle between them.

Cheers,
Jon

Originally Posted by jon3950

Your first sentence is correct.

Friction, or your resistance, is simply the force applied normal (or perpendicular) to the surface multiplied by the co-efficient of friction. The area has no effect.

The torque you apply to the nut rotates it, thus moving it down the thread on the bolt. Moving it down the bolt pushes it against the mating surface. This applies a force to the surface. It doesn’t matter how big the area of the mating surfaces are, the force applied is the same. (The pressure on the surface will change because pressure equals force divided by area.)

Because the nut is turning, it is also trying to move across the surface and friction is the force resisting this movement.

If the mating surface is flat then the normal force is the full force applied. If the surface is tapered then the normal force is the applied force multiplied by the sine of the angle between them.

Cheers,
Jon

Im going to have to read that a few times and scratch my noodle to get my head around but thankyou for the reply.

"The pressure on the surface will change because pressure equals force divided by area."
"It doesn’t matter how big the area of the mating surfaces are, the force applied is the same"

Dont those 2 sentences contradict one another?

What an interesting topic this has become.

Originally Posted by DAMINK

Im going to have to read that a few times and scratch my noodle to get my head around but thankyou for the reply.

"The pressure on the surface will change because pressure equals force divided by area."
"It doesn’t matter how big the area of the mating surfaces are, the force applied is the same"

Dont those 2 sentences contradict one another?

What an interesting topic this has become.

No they don’t as pressure isn’t force. I probably haven’t explained it as well as I could have as its a bit difficult doing it on the run. Its all basic physics though. Try googling it, there’s lots of good stuff out there and a diagram would probably help.

Cheers,
Jon

Originally Posted by jon3950

No they don’t as pressure isn’t force. I probably haven’t explained it as well as I could have as its a bit difficult doing it on the run. Its all basic physics though. Try googling it, there’s lots of good stuff out there and a diagram would probably help.

Cheers,
Jon

Decided to google it.

"From tests, it is known that approximately 50% of the tightening torque is dissipated in overcoming friction under the bolt head or the nut face (whichever is the face that is rotated). Typically only 10% to 15% of the overall torque is actually used to tighten the bolt, the rest is used to overcome friction in the threads and on the contact face that is being rotated (nut face or bolt head)."

Source http://www.boltscience.com/pages/nutorbolttightening.htm