Torque Wrenches - PITA

Flukester

Flukester

Flukester

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So I thought I'd retighten all my bikes caliper bolts with a shiny new screwfix torque wrench.... you know, do things properly.

Tighten, yep click, Tighten another, roger click, Tighten another, clickety, Tighten another (silence)..Tighten some more (silence) CRACKKKKKKKKKK!!!!

Nice one screwfix you bunch of &*^&, one snapped caliper casting.

Allen bolt in question was pin holding pads in... after speaky with local dealer they agreed, don't use a torque wrench on small bolts, just guess it with hand.

£200 quid down the drain :rolleyes::confused::eek::(:o
 
Torque wrenches are over rated for anything other than cases where you want to be certain of equal pressure eg cyclinder heads. I've never used one in 20 years of servicing my own bikes and cars (well, havent serviced my own car for a wahile but I used to) Never had anythign drop off yet!
 
a screw fix wrench isnt going to be the best, ive got a couple nice ones and even those like to go silent sometimes :( i test it before i start though to try and be safe
 
My Halfrauds TW has never ever let me down in the 10 years I've had it. Make sure you store it correctly and wind off the settings after each use and they should last years.
 
it is possible that the thread was already stripping, so as you were turning it wasnt reaching the preset torque and eventually something broke *shrug*
 
I have always been a bit confused over this, you can tighten it until it clicks. However theroy should surely be if you try again it should click and not turn. However the one I have will turn then click again, and again. So is that right or is it just a naff wrench?

Should you just stop as soon as it clicks and leave it?
 
With torque wrenches you need to make shure it has released before attemting to tighten the next bolt, listen for the first click to say the bolt is torqued down and then listen for the second click as the wrench releases.
 
Capt Doufos said:
I have always been a bit confused over this, you can tighten it until it clicks. However theroy should surely be if you try again it should click and not turn. However the one I have will turn then click again, and again. So is that right or is it just a naff wrench?
Click to expand...

Depends on what your tightening. If the assembly has something that could relax as pressure is applied to it, then you could expect this behaviour. Ordinarily "stiction" would make sure the torque wrench clicked before the fastener turned.
 
The reason it did not click is because it is too big of a wrench for its application. If you use such a big wrench for such small torque, you will miss the click if you are applying the load gently. The key of using big torque wrenches on small torques is to do it quickly. The torque might not be as accurate but you at least wouldn't miss the click and end up yielding the bolt/ stripping the thread.

I have the screwfix 15 quid job and I wouldn't use it for anything under say 40Nm. Get a smaller wrench for 22Nm.

Yes, torque is not important, but the clamping force is. If there isn't enough clamping force, the bolt will come loose under vibration. If there is too much, the joint will yield somewhere. The joint yielding somewhere is even worse than it snapping because you will end up with less clamping force and the joint is likely to come loose.

Torque is just an indication of the clamping force, there are many other factors that affect the torque/clamping force relation e.g. lubrication, condition of the thread etc. So even with a torque wrench, you are not necessarily safe.

For older bolts, always use copper slip because copper slip has about the same coefficient of friction as a new bolt.

If you are experience enough, you probably don't need a torque wrench as you can probably feel just about the right torque and you will definitely feel it if the joint start yielding. You are also quite likely to get away with it because the range for a correct clamping force is usually quite high.
 
nicholas_yiu said:
The reason it did not click is because it is too big of a wrench for its application. If you use such a big wrench for such small torque, you will miss the click if you are applying the load gently. The key of using big torque wrenches on small torques is to do it quickly. The torque might not be as accurate but you at least wouldn't miss the click and end up yielding the bolt/ stripping the thread.

I have the screwfix 15 quid job and I wouldn't use it for anything under say 40Nm. Get a smaller wrench for 22Nm.

Yes, torque is not important, but the clamping force is. If there isn't enough clamping force, the bolt will come loose under vibration. If there is too much, the joint will yield somewhere. The joint yielding somewhere is even worse than it snapping because you will end up with less clamping force and the joint is likely to come loose.

Torque is just an indication of the clamping force, there are many other factors that affect the torque/clamping force relation e.g. lubrication, condition of the thread etc. So even with a torque wrench, you are not necessarily safe.

For older bolts, always use copper slip because copper slip has about the same coefficient of friction as a new bolt.

If you are experience enough, you probably don't need a torque wrench as you can probably feel just about the right torque and you will definitely feel it if the joint start yielding. You are also quite likely to get away with it because the range for a correct clamping force is usually quite high.
Click to expand...
torque is also important for certain bolts. tiny m6 bolts that hold up golf sumps are meant to go to 25nm (whatever..) but once the bolt has stretched and killed its thread that badly, there is bearly any clamp force on the gasket

an m6 bolt shouldnt be going much more than 10-15nm. mine are all at 10nm and its perfect (one thing that doesnt actually leak!)
 
Matt82 said:
torque is also important for certain bolts. tiny m6 bolts that hold up golf sumps are meant to go to 25nm (whatever..) but once the bolt has stretched and killed its thread that badly, there is bearly any clamp force on the gasket

an m6 bolt shouldnt be going much more than 10-15nm. mine are all at 10nm and its perfect (one thing that doesnt actually leak!)
Click to expand...

Of course there is no tension, because once the bolt/thread is past its yielding point, the clamping force will keep on reducing however much torque you put down.

People always get confused about torque, torque is just an indication of the tension in the bolt (i.e. clamping force) there are so many other factors that can affect the bolt tension so you cannot rely on the torque only to be 100% safe.

For example, in my workplace, a whole batch of bolts are scraped because they tend to yield. The operators applied the correct torque but the bolts yielded because the surface finish under the bolt head is different from before.

That's the reason I say torque is not important, but clamping force (bolt tension) is.
 
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