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Interesting comment Michael. Some years ago when visiting a
workshop/factory that sealed porous engine blocks with the Locktite
product they had a chart on the wall showing the impact of what you mention
as important factors in how much of the torque figure showing on the tool
readout, or click setting;
Absorbed by friction in the dirty or damaged thread?
How much by the out of square nut : washer:clamping surface?
How much to the cheap commercial washers, not hardened washers?
How much due to no lubrication?
The chart showed that with the same torque reading the clamping force and
that is what we are trying to achieve is severely reduced by some of the
conditions and this is hard to quantify but the significant result for me
was with the same torque setting on the tool when the thread was clean and
in good condition the correct washer and grade of nut used with a light oil
lubricant the clamping force was much closer to the value indicated by the
torque reading. But when lubricated with Locktite it was possible to shear
the bolt
This shows how accurate or inaccurate the effect of the torque reading can
be
Serious engine builders do not use a torque wrench but measure the actual
effect required and that is clamping force plus an allowance for expansion
due to lpad and heat. Therefore they stretch the bolt to a predetermined
figure. In this situation 'more is not necessarily better'
As a side the Australian Standards for Industrial Fasteners will not use
Torque figures foe structual grade bolts. Don=B9t ask how I know this. I do
know that all the high strength bolts in a freeway bridge already assembled
and torqued up were required to be removed, replaced and new bolts installe=
d
by the calculated 'turn of nut' measurement system using hardened washers
Joe
From: Michael Salter <michaelsalter@gmail.com>
Date: Friday, 16 January 2015 8:53 AM
To: "healeys@autox.team.net" <healeys@autox.team.net>
Subject: Re: [Healeys] [SUSPECTED SPAM] Re: torque wrench
Way back in the "olden days" when I was doing my aircraft engine fitter
training we were given a graphic demonstration of just how varied the
clamping force that a nut tightened using an accurately calibrated torque
wrench could be.
Forget the 2 - 5% inaccuracy of the wrench and concentrate on clean, unworn
and correctly formed threads, proper countersinking at the top of stud
threads, sufficient thread below the nut, correct lubrication of the
threads, perfectly straight studs, serrated washers or soft washer
materials, correct tightening sequence etc etc..
When you see how those factors can affect the clamping forces the accuracy
of the torque wrench, which BTW in the services had to be checked daily, yo=
u
realize that the torque wrench is only a part of the equation!!
Michael S
BN1 #174
>=20
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<html><head></head><body style=3D"word-wrap: break-word; -webkit-nbsp-mode: s=
pace; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size:=
14px; font-family: Calibri, sans-serif; "><div>Interesting comment Michael.=
Some years ago when visiting a workshop/factory that sealed porous en=
gine blocks with the Locktite product they had a chart on the wa=
ll showing the impact of what you mention as important factors in how much o=
f the torque figure showing on the tool readout, or click setting;</div><div=
><span class=3D"Apple-tab-span" style=3D"white-space:pre"> </span>Absorbed
>by fr=
iction in the dirty or damaged thread?</div><div><span class=3D"Apple-tab-span=
" style=3D"white-space:pre"> </span>How much by the out of square nut :
washer=
:clamping surface?</div><div><span class=3D"Apple-tab-span"
style=3D"white-space=
:pre"> </span>How much to the cheap commercial washers, not hardened washers=
?</div><div><span class=3D"Apple-tab-span" style=3D"white-space:pre">
</span>How=
much due to no lubrication?</div><div><br></div><div>The chart showed that =
with the same torque reading the clamping force and that is what we are tryi=
ng to achieve is severely reduced by some of the conditions and this is hard=
to quantify but the significant result for me was with the same torque sett=
ing on the tool when the thread was clean and in good condition the correct =
washer and grade of nut used with a light oil lubricant the clamping force w=
as much closer to the value indicated by the torque reading. But when lubric=
ated with Locktite it was possible to shear the bolt</div><div><br></div><di=
v>This shows how accurate or inaccurate the effect of the torque readi=
ng can be</div><div><br></div><div>Serious engine builders do not use a torq=
ue wrench but measure the actual effect required and that is clamping force =
plus an allowance for expansion due to lpad and heat. Therefore they stretch=
the bolt to a predetermined figure. In this situation 'more is not necessar=
ily better'</div><div><br></div><div>As a side the Australian Standards for =
Industrial Fasteners will not use Torque figures foe structual grade bolts. =
Don’t ask how I know this. I do know that all the high strength bolts =
in a freeway bridge already assembled and torqued up were required to be rem=
oved, replaced and new bolts installed by the calculated 'turn of nut' measu=
rement system using hardened washers</div><div><br></div><div>Joe</div><div>=
<br></div><span id=3D"OLK_SRC_BODY_SECTION"><div style=3D"font-family:Calibri;
f=
ont-size:11pt; text-align:left; color:black; BORDER-BOTTOM: medium none; BOR=
DER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT=
: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP=
: 3pt"><span style=3D"font-weight:bold">From: </span> Michael Salter <<a hr=
ef=3D"mailto:michaelsalter@gmail.com";>michaelsalter@gmail.com</a>><br><span=
style=3D"font-weight:bold">Date: </span> Friday, 16 January 2015 8:53 AM<br><=
span style=3D"font-weight:bold">To: </span> "<a
href=3D"mailto:healeys@autox.tea=
m.net">healeys@autox.team.net</a>" <<a href=3D"mailto:healeys@autox.team.ne=
t">healeys@autox.team.net</a>><br><span style=3D"font-weight:bold">Subject:=
</span> Re: [Healeys] [SUSPECTED SPAM] Re: torque wrench<br></div><div><br>=
</div><div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:comic
san=
s ms,sans-serif;font-size:small">Way back in the "olden days" when I was doi=
ng my aircraft engine fitter training we were given a graphic demonstration =
of just how varied the clamping force that a nut tightened using an accurate=
ly calibrated torque wrench could be.<br>Forget the 2 - 5% inaccuracy of the=
wrench and concentrate on clean, unworn and correctly formed threads, prope=
r countersinking at the top of stud threads, sufficient thread below the nut=
, correct lubrication of the threads, perfectly straight studs, serrated was=
hers or soft washer materials, correct tightening sequence etc etc.. <br>Whe=
n you see how those factors can affect the clamping forces the accuracy of t=
he torque wrench, which BTW in the services had to be checked daily, you rea=
lize that the torque wrench is only a part of the equation!!<br><br></div><d=
iv class=3D"gmail_default" style=3D"font-family:comic sans
ms,sans-serif;font-si=
ze:small">Michael S<br></div><div class=3D"gmail_default"
style=3D"font-family:c=
omic sans ms,sans-serif;font-size:small">BN1 #174<br></div></div><div class=3D=
"gmail_extra"><div class=3D"gmail_quote"><blockquote class=3D"gmail_quote"
style=
=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div c=
lass=3D"h5"><br></div></div></blockquote></div></div></span></body></html>
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