All you can do is buy brand names from a reputable source, and then hope.
As a matter of interest, are you SURE that your torque wrench is reasonably correct?
David
Hi all,
Torqued up some 8.8 grade M8 bolts (Zinc plated). Looked up the required torque as 30 NM. Bolt's streched before this, what am I doing worng?
I think these bolts marked incorectly!! Anyone else come across this?
Cheers
Dan
There are a lot of counterfeit bolts out there - it's very scary when you think about it. Even worse, there's a high level of counterfeiting
in aircraft components! Now that's REALLY scary...
All you can do is buy brand names from a reputable source, and then hope.
As a matter of interest, are you SURE that your torque wrench is reasonably correct?
David
torque wrenches should be left unwound or the spring can get pretensioned or stretch and give an inaccurate reading...
Ned.
even at 20% out 30nm is sod all, a grade 8.8 should easily withstand a lot more than that.
(i have no idea what i'm talking about just my own personal, non scientific view)
Roughly 22 ft/lb, according to my converter program.
That's quite a lot for a M8 bolt if it's not high-tensile.
David
30Nm is too much for an 8.8 M8 according to this ref:
http://www.nord-lock.com/default.asp?url=338.16.37
and here
www.norbar.com/content/cms/TorqueValueGuide.pdf
[Edited on 23/6/06 by iank]
Iank, I think it's just correct, as it was a zinc plated bolt and nut so a 1.2 multiplyer of 25.5Nm is 30.6Nm...
Also checked torque wrench with scales, needs 7kg at 43cm, wich I recon is 30Nm.
Tried to diffrent bolts from the same supplyer same thing happed.. Did'nt get anywere near 30NM before it felt odd...
Dan
quote:
Did'nt get anywere near 30NM before it felt odd...
Not an expert by any means, but that first link claims 24.5 Nm for zinc plated 8.8 M8 assembled dry.
But I agree that is recommended torque not torque to kill the thing, there should be a heafty safety margin built into those figures. If it stretched
much earlier than 30 then something is clearly wrong!
Might be worth calling Namrick (http://www.namrick.co.uk) or someone else reputable to get their opinion, and order some decent ones.
what are you bolting?
quote:
You're not torquing into Aluminium are you? Could be close to stripping threads rather than stretching bolts!
o.k;
Not bolting Ali.
Nut and bolt both BZP, 8.8 M8. Nut is a nyloc, both new from supplyer.
It's for the handbrake lever (don't realy need this much torque I guess), but that's not the point, it makes all the other nut's
and bolts suspect I have from this supplyer.
It's a good job I know where all these nuts and bolts are at the moment
(two are holding the Master cylinder on).
[Edited on 23/6/06 by Bluemoon]
30Nm isn much, really, but you really don need it for a handbrake lever. However, if you want to be sure, swich to allen bolts, which are grade 12.9
and there is no way to miss.
just a suggestion...
by the way, zinc plating (as any electrolytic treatment) causes stress risers, so they are usually not as strong as non-plated ones)