Something I need to torque about..

[the great roberto]

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

Real real important that one. lub a fastener (usually a good thing to do ) like the wheel bolts on your car, and remember to lower the recommended torque value. Feels wrong, 'cause the bolt feels easier to tighten. Exactly, and easier to yield as well 'cause you've reduced the thread friction by lub'ing

 

[the great roberto]

just had word back from thomson and it says

"Grease on threads only, no use of anti-seize."

so it looks like their torque values require the screws to greased prior to torqueing. Makes sence.

 

[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:

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

This has been stored in my favorites for ages :

http://www.boltdepot.com/fastener%2Dinf ... Chart.aspx

I seem to recall SS A4 being a bit stronger than A2 and Ti being weaker than expected - similar to 10.9 ?

WD

 

[the great roberto]

a4 is 316 and a2 is 304.

316 is used for its corrosion properties against salt water.

316 uts is around 580MPa
304 is around the same !

titanium about 900 MPa
2000 series ali 480MPa

all of these at room temp.Add some temp and it all goes south big time.Time for some CMV steel then !!

 

[dyna-ti]

14.9 ?

And God says unto Issac -
If you'd done that up properly,your wheel wouldn't have fallen off!

 

[chiswickcollectables]

Ok... it's getting quite in-depth but interesting nonetheless. I think when funds permit I'll purchase a wrench and have a little play around. I tend to find that over time my seatpost definitely drops which is obviously due to me not tightening the bolt/clamp enough. I guess I'm a little over paranoid of damaging the frame by overtightening.

CB

 

[Flat Lander]

If you're going to get a torque wrench think carefully about the range you want to use it on. This usually means you need more than one :roll:

I'm pretty sure The great Roberto has got some advice on this topic too. Right matey?

 

[Flat Lander]

e.g. 5-20nm which is not enough for the M970 xtr crank.

Matey, do you use a torque wrench?

 

[haggis]

Roberto you forgot to mention the coefficient of friction of different anti seizes and the effect that has on torque values :roll:

 

[the great roberto]

Roberto you forgot to mention the coefficient of friction of different anti seizes and the effect that has on torque values :roll:

Ahhhhhhhhhhh. So you want the master class then

Yes, different lubs will reduce the friction between the threads.So, a class 1 lub will reduce the most and the now lub'd torque figure may need to be reduced even further to prevent over-torqueing and potential yield.

Tob be fair despite what manufacturers say, its a bit of guess work.
A good rule of thumb is to go for 50% reduvtion from dry quoted figure.

And anyway who uses a calibrated torque wrench that is checked pre and post use anyway ?