Something I need to torque about..

[Scrat]

I have all the correct torque wrenches!
from 0-300Nm

And they only ever come out when USA lawers are sniffing round.
or our ISO9001 is due :shock:

 

[Dr.Robotnik]

Feel is better than a torque wrench. Just don't do things up stupidly tight.

 

[the great roberto]

Torqueing a fastener is a crude means to an end.

Think about what you are actually trying to achieve.


A fastener works, because it clamps two or more items in place. The fastener does this because it is (elastically) strained. i.e. streached, such that it wants to go back to its un-streached state, and hence the clamping force.

ideally to get the correct amount of strain you would stretch the bolt, then apply a nut to hold the bolt in it's streached state. Thats how big fasteners are loaded. This load is periodically checked to make sure the load is still being applied.

A quick and dirty method is to torque a fasetner as a guide to how much it has been streached. However a torque value needs to be qualified.Is the fastener dry or lubricated ? normal practise is that you reduce the torque value by half is the threads are lub'd.

So, on a bike, when thomson tell me my stem bolts should be torqued to 4.0NM is that dry or lub'd. Their leaflet shows grease being applied to the threads, but i thienk that 4.0NM of torque applied to the lub'd fastener may result in the fastner yielding.i.e. being strained plastically, and thus not actually providing any clamping force.

must email them and ask !


Despite the above, a simple torque wrench is useful in certain critical areas of a bike, car, or even a nuclear power station. Use it in the knowledge that you have taken the manufacturers advice.

 

[WD Pro]

Feel is better than a torque wrench. Just don't do things up stupidly tight.

Not quite sure I agree with that ...

My 'stupidly tight' is a whole world apart from my GF's 'stupidly tight'

Another reason that I dont like the allen ket sets etc that are in the pocket holder thingies - its possible to apply the same amount of leverage to the small key as the large as you are using the same handle

WD

 

[WD Pro]

Torqueing a fastener is a crude means to an end.

Think about what you are actually trying to achieve.


A fastener works, because it clamps two or more items in place. The fastener does this because it is (elastically) strained. i.e. streached, such that it wants to go back to its un-streached state, and hence the clamping force.

ideally to get the correct amount of strain you would stretch the bolt, then apply a nut to hold the bolt in it's streached state. Thats how big fasteners are loaded. This load is periodically checked to make sure the load is still being applied.

A quick and dirty method is to torque a fasetner as a guide to how much it has been streached. However a torque value needs to be qualified.Is the fastener dry or lubricated ? normal practise is that you reduce the torque value by half is the threads are lub'd.

So, on a bike, when thomson tell me my stem bolts should be torqued to 4.0NM is that dry or lub'd. Their leaflet shows grease being applied to the threads, but i thienk that 4.0NM of torque applied to the lub'd fastener may result in the fastner yielding.i.e. being strained plastically, and thus not actually providing any clamping force.

must email them and ask !


Despite the above, a simple torque wrench is useful in certain critical areas of a bike, car, or even a nuclear power station. Use it in the knowledge that you have taken the manufacturers advice.

Some very good points

I have noticed in 'some' manuals it not only says in text if the setting is wet or dry but also (if wet) the spec of the oil / grease / thread lock etc that should be used

ARP sell devices (or have done in the past) to measure bolt 'stretch' rather than trust torque only good if you can get to both ends though … :-(

Some specs for thread lock make reference to the effect on torque

Although it can be a bit of a minefield, I still think a basic torque wrench is a great addition for the home mechanic - especially after witnessing dad's technique of 'four white knuckles' ...

WD

 

[lewis1641]

However a torque value needs to be qualified.Is the fastener dry or lubricated ? normal practise is that you reduce the torque value by half is the threads are lub'd.

:shock:

never knew that

 

[the great roberto]

elastic strain is the key. plastic strain(yield)=FUBAR.

The grading of fasteners tells you the ultimate tensile strength(uts) , i.e goes snap and the percentage yield point of that UTS i.e. 8.8 or 10.8 or 14.9.

so a 14.9 cap head screw has a high uts and yields at 90% of that uts.

most regular bolts are 6.8 grade. little more than compressed dog shite :cry:

 

[WD Pro]

elastic strain is the key. plastic strain(yield)=FUBAR.

The grading of fasteners tells you the ultimate tensile strength(uts) , i.e goes snap and the percentage yield point of that UTS i.e. 8.8 or 10.8 or 14.9.

so a 14.9 cap head screw has a high uts and yields at 90% of that uts.

most regular bolts are 6.8 grade. little more than compressed dog shite :cry:

14.9 ? :shock:

 

[Neil G]

Don't you just do it up till thread starts coming out and then back it off 1/4 turn?

No I normally keep going 'til the allen key snaps

lol or something rounds off!

 

[the great roberto]

elastic strain is the key. plastic strain(yield)=FUBAR.

The grading of fasteners tells you the ultimate tensile strength(uts) , i.e goes snap and the percentage yield point of that UTS i.e. 8.8 or 10.8 or 14.9.

so a 14.9 cap head screw has a high uts and yields at 90% of that uts.

most regular bolts are 6.8 grade. little more than compressed dog shite :cry:

14.9 ? :shock:

not that common, but 12.9 are.

from memory............the 8 means 800 MPa. i.e. 800 mega pascals or 800 mega n/mm squared. then the .8 means that it yields at 80% of the 800MPa.

So a 14.9 has a high uts and a high yield point.

stainless A2 or A4 bolts are quite soft and hence a uts of about 600MPa. That is why stainless looks nice but iscrap at any significant load.

ummmmmmmmm must look up titanium