OT - Torque the Nut or the Bolt?
DerbyDad03
looking for some input.
Let's say I've got a nut and bolt holding something together and I
want it torqued at XXX inch-pounds. I can hold the nut with a standard
wrench and use the torque wrench on the bolt, or I can hold the bolt
with a standard wrench and use the torque wrench on the nut.
One of the guys I was working with said "When given the chance, you
always torque the nut." When I asked why the answer was "Because
that's what I've always been told." You know how *those* conversations
go!
So what's the deal? Does it matter? And if so, why? Could it be
different in different cases? And if so, why?
Thanks!
Oren
I follow the reference manual. Either torque the bolt or the nut. When
a pattern of torque is necessary, like with head bolts..follow the
instructions.
I replaced my radial arm bushings on the truck. The ONLY option was to
torque the nut.
dpb
The "guy" is right because the torque spec will be for the fastener. If
turn from the bolt side instead of the nut, there's a possibility
there's additional friction (almost guaranteed) along the side of the
bolt that isn't there on the nut side. Consequently, one will end up
low on the torque spec; how much depends on the unknown internal force
having to overcome w/ the bolt itself.
--
mike
It does not matter. The braking effect of the underside of the nut is
equivalent to the braking effect of the underside of the bolt head.
DerbyDad03
> On Jun 30, 12:40 pm, DerbyDad03 <teamarr...@eznet.net> wrote:
>
>
>
>
>
> > This question came up while working on a project this weekend and I'm
> > looking for some input.
>
> > Let's say I've got a nut and bolt holding something together and I
> > want it torqued at XXX inch-pounds. I can hold the nut with a standard
> > wrench and use the torque wrench on the bolt, or I can hold the bolt
> > with a standard wrench and use the torque wrench on the nut.
>
> > One of the guys I was working with said "When given the chance, you
> > always torque the nut." When I asked why the answer was "Because
> > that's what I've always been told." You know how *those* conversations
> > go!
>
> > So what's the deal? Does it matter? And if so, why? Could it be
> > different in different cases? And if so, why?
>
> > Thanks!
>
nut is equivalent to the braking effect of the underside of the bolt
head
Even if the material on the underside of the nut is not equivalent to
the material on the underside of the bolt head?
dpb
Not normally as quite often there will be lock washer under the nut not
under the head and, as noted above, there's drag along the length of the
fastener for the bolt that isn't present for the nut. This effect
varies from insignificant to possibly quite large depending on the
application and size of bolt/hole/what the bolt is bearing on, if anything.
--
SteveB
"DerbyDad03" <teama...@eznet.net> wrote in message
news:36ddab12-99df-4bbf...@y21g2000hsf.googlegroups.com...
What if there is no nut, as when a bolt goes into a block? Or what if there
is no bolt, as when a nut goes on a stud?
As for me, I would think any time there is a bolt that it can have added
resistance from whatever it is seated against, and if you were to use a
clicking torque wrench after tightening it down manually, that the wrench
would give different readings from the nut and the bolt, and I suspect the
bolt reading would be higher.
Steve
mike
>
> - Show quoted text -
In such a case the difference would still likely be minimal. It's not
like you're going to use an aluminum nut with steel bolt.
Torque specs vary on bolt size, bolt strength, application
(permanent, non-permanent, etc.) and lubrication or lack thereof.
They don't vary on which half of the fastener is experiencing sliding
friction.
mike
>
> - Show quoted text -
As a self-follow-up, I think if all fasteners looked like this:
http://accuratemfg.com/images/ComboHeadSexBolt.jpg
...nobody would even ask the question.
dpb
...
> Torque specs vary on bolt size, bolt strength, application
> (permanent, non-permanent, etc.) and lubrication or lack thereof.
> They don't vary on which half of the fastener is experiencing sliding
> friction.
Correct, so _if_ one portion of the fastener (namely the bolt) _does_
have a friction load, the net torque applied will be low as compared to
the spec.
For most relatively small bolts and applications, the effect is probably
minimal, granted, but the general principle holds.
--
mike
> mike wrote:
>
> ...
>
> > Torque specs vary on bolt size, bolt strength, application
> > (permanent, non-permanent, etc.) and lubrication or lack thereof.
> > They don't vary on which half of the fastener is experiencing sliding
> > friction.
>
> Correct, so _if_ one portion of the fastener (namely the bolt) _does_
> have a friction load, the net torque applied will be low as compared to
> the spec.
>
No the torque spec will not be low. Both the nut and the bolt would
have frictional resistance on the underside if turned. See the
picture in this thread so you can see the symmetry of a bolted joint.
The placement of the threads doesn't affect the frictional symmetry.
DerbyDad03
> "DerbyDad03" <teamarr...@eznet.net> wrote in message
>
> news:36ddab12-99df-4bbf...@y21g2000hsf.googlegroups.com...
>
>
>
>
>
> > This question came up while working on a project this weekend and I'm
> > looking for some input.
>
> > Let's say I've got a nut and bolt holding something together and I
> > want it torqued at XXX inch-pounds. I can hold the nut with a standard
> > wrench and use the torque wrench on the bolt, or I can hold the bolt
> > with a standard wrench and use the torque wrench on the nut.
>
> > One of the guys I was working with said "When given the chance, you
> > always torque the nut." When I asked why the answer was "Because
> > that's what I've always been told." You know how *those* conversations
> > go!
>
> > So what's the deal? Does it matter? And if so, why? Could it be
> > different in different cases? And if so, why?
>
> > Thanks!
>
what if there is no bolt, as when a nut goes on a stud?
Thanks for the response, but I'm not sure why you asked those
questions.
I stated what my situation was: I've got a nut and bolt holding
something together. Obviously if there is not one or the other, you
have no choice as to where you use the torque wrench.
I'm probably missing the point of your questions. Please elaborate.
> As for me, I would think any time there is a bolt that it can have added
> resistance from whatever it is seated against, and if you were to use a
> clicking torque wrench after tightening it down manually, that the wrench
> would give different readings from the nut and the bolt, and I suspect the
> bolt reading would be higher.
>
> Steve- Hide quoted text -
DerbyDad03
>
> - Show quoted text -
Not sure I understand your point. If all fasteners look like this, no
one would ask the question either:
http://image.guardian.co.uk/sys-images/Arts/Arts_/Pictures/2006/11/28/paperclip460.jpg
However, the fastener in my picture does not fit all applications, and
neither does yours.
dpb
There can be friction along the _LENGTH_ of the bolt which must be
turned which, if present, is _NOT_ symmetric as turning the nut doesn't
require turning the bolt against that load.
--
DerbyDad03
>
> - Show quoted text -
Not everything comes with a manual. This is a custom built project.
dpb
...
> Not everything comes with a manual. This is a custom built project.
Then you get to set the torque specs... :)
--
SteveB
Just that I think in a real time test that if you were to torque two bolt
and nuts on identical assemblies, torquing the bolt on one, and the nut on
the other, that when you popped them loose, the torque readings would be
different.
And that sometimes, there IS no nut or bolt to select from. You have one or
the other.
Trouble is, if it is important enough to have a torque rating, failure will
probably be highly damaging.
Steve
dpb
...
> Thanks for the response, but I'm not sure why you asked those
> questions.
Because he didn't read the original question??? :)
> I stated what my situation was: I've got a nut and bolt holding
> something together. Obviously if there is not one or the other, you
> have no choice as to where you use the torque wrench.
...
Choose the nut if you can. Again, if there's no side load on the bolt
(that is, it turns freely in the hole) there will be virtually no
difference. _IF_ (again, the proverbial "big if") there is a resistance
on the bolt, whatever that torque that resistance contributes is will
contribute to the reading of the torque wrench so the actual torque
applied to the fastener will be low by that amount.
In normal situations, again, as noted, this will be small, but it's more
consistent to stay w/ the nut end.
--
Don Young
A lot of good responses here. It may help to know that without controlled
testing of a particular fastening application, tightening to a torque value
is only a very gross approximation to whatever tension the fastener can
withstand or the parts being held require. If you want to tighten to the
fastener limit, torque at least 6 to failure, verifying that the results are
reasonably consistent. Then set the torque at about 65% of the lowest. If
your concern is how much torque is required to hold the parts satisfactorily
you will need to test that. Sometimes uniform torque/tension is more
important than the specific amount, such as for cylinder heads.
Torquing the bolt or nut will make no consistent measureable difference. The
properties of the materials mating surfaces such as shape, hardness,
roughness, and lubrication will have significant effects. It's an
interesting thought but has no practical application that I am aware of.
The purpose of tightening a bolt is to stretch it (like a very stiff spring)
so that it will maintain the tension needed. If the amount of tension is
pretty important, then tension indicating or torque-to-yield fasteners are
sometimes used. On old Triumph motorcycles you tensioned the rod bolts by
measuring the stretch with a micrometer. This will give much more consistent
results than a torque wrench and can be used to test whether there is any
consistent difference in turning the bolt or the nut.
Don Young
SteveB
"Don Young" <no...@nonesuch.com> wrote in message
news:j6KdnbQLCbm9OvTV...@posted.worldwebinternetservicesprovideinc...
Your statements are true, but come with some assumptions. That is the parts
of the fastener are clean, the hole through which they pass is clean, the
threads are not boogered up, there is no corrosion or galling, and a couple
of other things. By and large, it don't make a lot of difference, but in
cases where the fastener is stuck on there because of various things, or the
hole is tight, or the fasteners have contamination in layers, or there is
any measurable metal damage, it can make a lot of difference.
Not picking nits here, but just to say that GENERALLY, it don't make much
differences, but not ALL the time. And we remember those odd instances
rather than the hundreds of times it goes by the book.
Or at least where I live.
Steve
Rick Brandt
> "DerbyDad03" <teama...@eznet.net> wrote in message
> news:71146b58-4029-4d25...@a70g2000hsh.googlegroups.com...
> what if there is no bolt, as when a nut goes on a stud?
>
> Thanks for the response, but I'm not sure why you asked those
> questions.
>
> I stated what my situation was: I've got a nut and bolt holding
> something together. Obviously if there is not one or the other, you
> have no choice as to where you use the torque wrench.
>
> I'm probably missing the point of your questions. Please elaborate.
These are discussion groups. You make a new post and a discussion is
started. If your original post asks a question then (if you're lucky) you
will get some answers somewhere in the thread. However; having the
discussion branch off in other directions is part of the package. There is
no requirement that the conversation stick to your original premise.
SteveB
"Rick Brandt" <rickb...@hotmail.com> wrote in message
news:iHoak.11830$jI5....@flpi148.ffdc.sbc.com...
There is in a perfect world.
DerbyDad03
> "DerbyDad03" <teamarr...@eznet.net> wrote in message
>
> news:71146b58-4029-4d25...@a70g2000hsh.googlegroups.com...
> On Jun 30, 7:21 pm, "SteveB" <toquerville@zionvistas> wrote:
>
>
>
> > "DerbyDad03" <teamarr...@eznet.net> wrote in message
>
> >news:36ddab12-99df-4bbf...@y21g2000hsf.googlegroups.com...
>
> > > This question came up while working on a project this weekend and I'm
> > > looking for some input.
>
> > > Let's say I've got a nut and bolt holding something together and I
> > > want it torqued at XXX inch-pounds. I can hold the nut with a standard
> > > with a standard wrench and use thetorquewrench on the nut.
>
> > > One of the guys I was working with said "When given the chance, you
> > > that's what I've always been told." You know how *those* conversations
> > > go!
>
> > > So what's the deal? Does it matter? And if so, why? Could it be
> > > different in different cases? And if so, why?
>
> > > Thanks!
>
> re: What if there is no nut, as when a bolt goes into a block? Or
> what if there is no bolt, as when a nut goes on a stud?
>
> Thanks for the response, but I'm not sure why you asked those
> questions.
>
> I stated what my situation was: I've got a nut and bolt holding
> something together. Obviously if there is not one or the other, you
> have no choice as to where you use thetorquewrench.
>
> I'm probably missing the point of your questions. Please elaborate.
>
> > As for me, I would think any time there is a bolt that it can have added
> > resistance from whatever it is seated against, and if you were to use a
> > would give different readings from the nut and the bolt, and I suspect the
> > bolt reading would be higher.
>
> > Steve- Hide quoted text -
>
> > - Show quoted text -
>
> A lot of good responses here. It may help to know that without controlled
> testing of a particular fastening application, tightening to atorquevalue
> is only a very gross approximation to whatever tension the fastener can
> withstand or the parts being held require. If you want to tighten to the
> reasonably consistent. Then set thetorqueat about 65% of the lowest. If
> your concern is how muchtorqueis required to hold the parts satisfactorily
> you will need to test that. Sometimes uniformtorque/tension is more
> important than the specific amount, such as for cylinder heads.
>
> Torquing the bolt or nut will make no consistent measureable difference. The
> properties of the materials mating surfaces such as shape, hardness,
> roughness, and lubrication will have significant effects. It's an
> interesting thought but has no practical application that I am aware of.
>
> The purpose of tightening a bolt is to stretch it (like a very stiff spring)
> so that it will maintain the tension needed. If the amount of tension is
> sometimes used. On old Triumph motorcycles you tensioned the rod bolts by
> measuring the stretch with a micrometer. This will give much more consistent
> consistent difference in turning the bolt or the nut.
>
>
> - Show quoted text -
Having absorbed all of the information given here, I've come to a
conclusion: I'll torque the nut.
For my application, I actually have 2 types of torque to deal with.
In one case, I want to torque the fastener to prevent all movement, so
I would want to torque the fastener to the maximum setting that will
not result in failure. For this case, knowing the failure point of the
bolt is required, assuming I test it from the same side (nut or bolt)
each time. Based on everything that has been said in this thread, it
sounds as if using the nut side makes the most sense. It just so
happens that it is physically easier to torque the nut anyway. :-)
In the other case, I want to allow for a certain amount of horizontal
rotational friction around the bolt. In other words, I want the object
that is fastened to be able to spin on the bolt, but not freely. In
this case, I will once again use the nut side for consistancy
purposes.
Thanks for all contributions to a lively discussion.
mike
>
> However, the fastener in my picture does not fit all applications, and
>
> - Show quoted text -
The point is that it does not matter where the threads are. The sex
bolt scenario is frictionally equivalent to a standard bolt scenario.
You still have two possible sliding regions (one under the nut and one
under the bolt head) that are identical.
Let's say that you put 100 joules into tightening the fastener. If
you turn the nut, the energy loss might be say 5 joules, leaving 95
joules to stretch the fastener properly. If you turn the bolt, the
energy loss would be the same, 5 joules, leaving the same 95 joules to
stretch the fastener.
Seriously, I'm done thinking of different ways to explain this. And
there is not significant energy loss along the sides of the through
hole. The tensioned surfaces (the threads and the regions under the
nut and bolt head) are the places where the braking effects occur.
dpb
...
> Seriously, I'm done thinking of different ways to explain this. And
> there is not significant energy loss along the sides of the through
> hole. ...
As long as there is no a significant side load, yes...if there is, then
it _is_ different.
--
mike
If there is significant side load on your bolt from the holes in the
plate stack, then how'd you get the bolt in the hole in the first
place?
Gordon Shumway
>There can be friction along the _LENGTH_ of the bolt which must be
>turned which, if present, is _NOT_ symmetric as turning the nut doesn't
>require turning the bolt against that load.
Anyone that has an engineering background knows you are correct.
However, I doubt that you will ever get that through to Mike.
dpb
Punch, usually...you never have anything difficult to line up? If not,
you've never worked on much...
--
mike
>
> - Show quoted text -
Rediculous. That's a great way to destroy the threads on a bolt.
dpb
...
> Rediculous. That's a great way to destroy the threads on a bolt.
_Drift_ punch in the hole, not on the bolt, silly...
--
Gordon Shumway
Mike,
Get your head out of your butt. "Punch" is a noun not a verb. You
use the punch to line up the holes before inserting the bolt.
Sit back and just read. You could learn a lot.
G.S.
mike
If you use tapered rods in neighboring holes to line things up... then
there is no side load on your bolt! It drops right in.
dpb
> On Jul 2, 8:39 am, dpb <n...@non.net> wrote:
>> mike wrote:
>>
>> ...
>>
>>> Rediculous. That's a great way to destroy the threads on a bolt.
>> _Drift_ punch in the hole, not on the bolt, silly...
>>
>> --
>
> If you use tapered rods in neighboring holes to line things up...
That "tapered rod" is a drift punch.
> ... then there is no side load on your bolt! It drops right in.
Sometimes yes, sometimes not so much.
--
mike
>
> - Show quoted text -
If the hole is lined up with taper rods, then the bolt drops in and
there is no "side load".
From Bolt Science.com:
"Typically only 10% to 15% of the overall torque is actually used to
tighten the bolt, the rest is used to overcome friction in the threads
and on the contact face that is being rotated (nut face or bolt head).
"
Notice that it doesn't say anything about the side of the bolt being
squeezed by the hole. It seems that you're the one with your head up
you butt.
dpb
...
> "Typically only 10% to 15% of the overall torque is actually used to
> tighten the bolt, the rest is used to overcome friction in the threads
> and on the contact face that is being rotated (nut face or bolt head).
> "
>
> Notice that it doesn't say anything about the side of the bolt being
> squeezed by the hole. It seems that you're the one with your head up
> you butt.
Notice it says "typically"...
Notice I have continually used "if" for the cases where it is/can be a
problem and have also continually pointed out it isn't significant where
there isn't a problem.
In addition to the misalignment problem, there are also assemblies where
the bolt may, in fact, be designed to carry a load (as in a hanger, for
example).
--
mike
I'm sorry, but you can't have it both ways. If you can install the
bolt, then there is no squeezing effect. If there is a squeezing
effect during installation, then you cannot install the bolt.
dpb
...
> I'm sorry, but you can't have it both ways. If you can install the
> bolt, then there is no squeezing effect. If there is a squeezing
> effect during installation, then you cannot install the bolt.
Sorry, but even if you can _TEMPORARILY_ counteract the force, you can't
always keep it from returning (external side load, for example).
If you think that isn't so, I reiterate you simply haven't worked on
enough stuff.
Have a nice day and hope all your assemblies are so simple...
--
DerbyDad03
> On Jul 2, 8:39 am, dpb <n...@non.net> wrote:
>
> > mike wrote:
>
> > ...
>
> > > Rediculous. That's a great way to destroy the threads on a bolt.
>
> > _Drift_ punch in the hole, not on the bolt, silly...
>
> > --
>
then there is no side load on your bolt! It drops right in.
Not so. In my application, the non-threaded portion of any given
number of bolts are known to be of varying diameters, as are the holes
of any given number of the object being fastened. There are times when
the bolt needs to be pressed while turned to insert or remove and
there are times when the bolt just drops right in. Since we are
required to obtain both the object and the bolts from a single source
we are stuck with what we get.
We prefer the tightest fit possible, which is why I concluded that
torqueing the nut is the correct method for us to use. If, in our
ideal situation, we have a very tight fit, then the side load on a
"big bolt/small hole" combination would impact our torque readings
considerably.
dpb
...
> We prefer the tightest fit possible, which is why I concluded that
> torqueing the nut is the correct method for us to use. If, in our
> ideal situation, we have a very tight fit, then the side load on a
> "big bolt/small hole" combination would impact our torque readings
> considerably.
Most definitely, tight tolerances are a prime example of where the side
pressure doesn't go away and where definitely for consistency from
assembly to assembly you would want to use the nut end.
"Mike" is simply too inexperienced apparently to have run into "real
world" complications to the theoretical descriptions he finds on the
web... :(
--
DerbyDad03
>
> - Show quoted text -
Unless I'm not understanding your use of the word "squeezing", I don't
agree.
As I said previously, certain combinations of bolt and object allow
for a "drop right in" situation, other combinations require turning/
pushing to get the bolt in.
Here is an example bolt in question:
http://www.cometkartsales.com/store/chassis/cpa/images/margayparts/markpbolt.jpg
The diameter of non-threaded portion of the bolt, as well as the
diameter of the hole it goes through, can be significantly different -
relatively speaking. If the hole happens to be in a 3/4" thick piece
of steel sitting on top of a 1" steel bushing, these different
diameters cold make a significant difference in side load.
There is also the issue quality control where it is possible that any
given hole might not be perfectly perpendicular to the faces. While
this will not only impact the sideload on the bolt, it introduces all
sort of other problems in the final product that I don't need to go
into here. Picture a bolt held straight by the bushing and then being
inserted into a 3/4" hole that is not perpendicular to the bushing. I
see significant sideload being introduced in the last 3/4".
SteveB
(end of transmission)
You may refer to my previous posts and applaud now.
Steve
DerbyDad03
> "DerbyDad03" <teamarr...@eznet.net> wrote in message
re: You may refer to my previous posts and applaud now.
If I wasn't so tired from reviewing this long thread, I'd stand up
too. ;-)
gpsman
> Having absorbed all of the information given here, I've come to a
> conclusion: I'll torque the nut.
Holy shit it doesn't matter. If you can reach both the bolt head and
the nut I'd have thought you'd have torqued 'em both and figgered it
out.
.
> For my application, I actually have 2 types of torque to deal with.
I doubt that.
> In one case, I want to torque the fastener to prevent all movement,
Good luck with that.
> so
> I would want to torque the fastener to the maximum setting that will
> not result in failure.
Fail... when?
> Based on everything that has been said in this thread, it
> sounds as if using the nut side makes the most sense.
Yeah, but there's only one "real" answer among "everything that has
been said in this thread"- Don Young's.
> In the other case, I want to allow for a certain amount of horizontal
> rotational friction around the bolt. In other words, I want the object
> that is fastened to be able to spin on the bolt, but not freely. In
> this case, I will once again use the nut side for consistancy
> purposes.
I hope this isn't a spacecraft.
-----
- gpsman
dpb
...
> Yeah, but there's only one "real" answer among "everything that has
> been said in this thread"- Don Young's.
Don's is precisely correct in what it deals with, but if there is a
tight fit of the bolt in the hole and one torgues the bolt and not the
nut, the reading of the torque wrench will include the resistance of the
bolt and the resulting applied torque will be low by that amount as
compared to what would be applied if torqued the nut.
That's all, no more, no less...
That the torque spec is an approximation and all that is certainly true,
but the real world still intrudes on what one will measure in different
circumstances.
--
DerbyDad03
re: I hope this isn't a spacecraft.
Why would anyone ask a spacecraft related question in a home repair
forum? Jeez.
gpsman
> gpsman wrote:
>
> ...
>
> > Yeah, but there's only one "real" answer among "everything that has
> > been said in this thread"- Don Young's.
>
> Don's is precisely correct in what it deals with, but if there is a
> tight fit of the bolt in the hole and one torgues the bolt and not the
> nut, the reading of the torque wrench will include the resistance of the
> bolt and the resulting applied torque will be low by that amount as
> compared to what would be applied if torqued the nut.
Your boat is too big for you ho.
-----
- gpsman
dpb
...
> Why would anyone ask a spacecraft related question in a home repair
> forum? Jeez.
Heck, somebody asked about nuclear power plants just the other day... :)
--
dpb
...
> Your boat is too big for you ho.
The question that started it off had tolerances that created the
situation. By some design standards that's so, but real world strikes
again...
And also there's the place where the bolt functions as a load-carrying
member, etc., etc., etc., ...
--
SteveB
Thank you. At least most of the usual suspects have agreed that 99% of the
time, it don't matter. And that was stated by, IIRC, all. The discussion
came about in circumstances that involve the other 1%, which is what I am
interested in. I know what happens when things go right. What I'm
interested in is those other times, because they are the ones that make it
interesting and labor intensive. ............. ez outs ......... drilling
.......... broken ez outs ............ torches ............ application of
heat, cold, penetrants, etc ................ learning new cuss words
........... getting out the first aid kit .........
need I go on?
Steve
gpsman
>
> The question that started it off had tolerances that created the
> situation. By some design standards that's so, but real world strikes
> again...
I don't care which world. How are you going to get your bolt
*through* hole and still retain enough friction between the two
surfaces to affect the torque wrench reading?
-----
- gpsman
dpb
Sometimes it's easy, sometimes it isn't...I've already gone thru it
enough times I no longer care.
OP's occasionally driving or pressing them, apparently, as I read his
post...
My practical problems tend to have weighted loads that aren't easy to
control in repair situations so one can manage to get the sucker in
there, but as soon as let go of the drift, it'll close up hard...
If that doesn't float your particular boat, so be it...
--
dpb
...
> OP's occasionally driving or pressing them, apparently, as I read his
> post...
...
Actually, it would be easy enough for him to test how significant it is
in his case--take one of his tightest-fit examples and torque it from
the bolt side, then check the nut end. If the drag is significant,
he'll find he can torque it further; if it only seems tight getting it
in the hole but isn't _that_ tight, it won't make a noticeable difference.
--
Tony Hwang
> This question came up while working on a project this weekend and I'm
> looking for some input.
>
> Let's say I've got a nut and bolt holding something together and I
> want it torqued at XXX inch-pounds. I can hold the nut with a standard
> wrench and use the torque wrench on the bolt, or I can hold the bolt
> with a standard wrench and use the torque wrench on the nut.
>
> One of the guys I was working with said "When given the chance, you
> always torque the nut." When I asked why the answer was "Because
> that's what I've always been told." You know how *those* conversations
> go!
>
> So what's the deal? Does it matter? And if so, why? Could it be
> different in different cases? And if so, why?
>
> Thanks!
Hi,
Do an experiment then. Torque the bolt and check the torque on the nut.
Is there difference? How much is the difference? Is the difference
enough to raise concern? Some times you can only access bolt or nut with
wrench, then what?
DerbyDad03
I have had cases where the bolt/hole combination has been *extremely*
tight. It required turning and tapping to insert the bolt. Now I think
I've got my ideal case, right?
Then I grab the toruque wrench and before I reach my desired setting,
the bolt snaps just below the threads. (The threads are, of course,
narrower than the shaft, so there is no friction between the threads
and the hole.) This raises the question of what caused the failure.
Was this bolt weaker than the others or did the fact that the bolt
could not twist/stretch in the hole cause to snap at a lower torque
than it could normally handle? Since most failures seem to occur with
the tighter bolts, either the larger bolts are weaker or the friction
prevents the stretching.
I'll vote for the friction.
TimR
> The purpose of tightening a bolt is to stretch it (like a very stiff spring)
> so that it will maintain the tension needed. If the amount of tension is
> pretty important, then tension indicating or torque-to-yield fasteners are
> sometimes used. On old Triumph motorcycles you tensioned the rod bolts by
> measuring the stretch with a micrometer. This will give much more consistent
> results than a torque wrench and can be used to test whether there is any
> consistent difference in turning the bolt or the nut.
>
> Don Young- Hide quoted text -
>
Good answer.
I would have worded it in reverse to make the point more clear. The
purpose of the torque is to get the clamping force correct. It is
correct that that should also stretch the bolt the correct amount in
order to meet the primary goal, the clamping force. How much the bolt
stretches, or whether it goes into yield or even fails, is determined
by the size of the bolt. So first you pick the force, then you use
that to pick the bolt size. And that is why you see eight sizes of
bolt on the same lawnmower - it's not really to make you buy eight
different wrenches, that's just a side benefit.
You also alluded to the difficulty of getting the accuracy. From what
I've seen, nobody with a torque wrench does any better than 50% plus
or minus his desired amount of torque, so which end you put the wrong
torque on is probably moot.
DerbyDad03
re: So first you pick the force, then you use that to pick the bolt
size.
Unless you have no choice as to the bolt size. Earlier I mentioned
that we are forced to single-source the bolt. Taking it to the next
level, we are required to purchase a *specific* bolt from that single
source.
Once we have the parts, the torque used to install them is up to us.
If I could purchase bolts from any source I wanted, things might be
different from a torque value perspective, but the original question
would still stand - nut v. bolt.
re: nobody with a torque wrench does any better than 50% plus or minus
his desired amount of torque
Please elaborate. Let's say I'm using a click wrench set to 200 in-
pounds. Are you saying my actual torque is anywhere from 100 to 300?
I'll assume that's not what you're saying since my assembly will
either be flopping around (relatively speaking) at 100 or the bolt
would have snapped well below 300.
TimR
> re: So first you pick the force, then you use that to pick the bolt
> size.
>
> Unless you have no choice as to the bolt size. Earlier I mentioned
> that we are forced to single-source the bolt. Taking it to the next
> level, we are required to purchase a *specific* bolt from that single
> source.
>
> Once we have the parts, the torque used to install them is up to us.
Yes, but how do you decide how much torque? Ideally, you know the
clamping force you want between the parts. Then you apply just enough
torque to get the clamping force. If you are forced to accept one
particular bolt, you run the risk that to get sufficient clamping
force you have to overtorque the bolt, risking failure, or undertorque
it, risking loosening in use. Do the calculation. If case 1, forget
it. If case 2, better use loctite, a very good lockwasher setup,
etc. Torque is there for a reason.
>
> re: nobody with a torque wrench does any better than 50% plus or minus
> his desired amount of torque
>
> Please elaborate. Let's say I'm using a click wrench set to 200 in-
> pounds. Are you saying my actual torque is anywhere from 100 to 300?
That seems strange to me too. But apparently that's what the studies
show. Also the torque can fail to have any correlation to the
clamping force.
By the way, torque is usually specified dry or wet. It's been decades
since I put a fastener on without lube, so I always look for wet. I
don't even like to put in a wood screw dry! <g>
And if I've got any of this wrong please correct me. Engineering
school was a .......long..........time ago and I may be
misremembering.
DerbyDad03
re: Yes, but how do you decide how much torque?
Trial and error over many years of experimenting. To prevent movement,
we go with the max before the bolt will fail, based on past
experience. In the other application, where we went to allow for
movement, that number might vary from installation to installation
based on how "loose" we want it - it's a case by case thing.
re: studies show...(the +/- 50% error)
Nothing personal, but I can't accept that without some substantiating
citations. If I were truly getting anywhere from 100 to 300 when my
click wrench says 200, then there is no way we could have zeroed in on
certain specific numbers that prove to work best time after time after
time. Why would we see bolts fail at a fairly consistant number that
is well below the upper range of a 50% error? I'll bet I could
consistantly snap the bolts at less than 10% above what we use as our
max number. Finally, the torque values we use work for our application
- and the bolt failure points are consistant - across multiple torque
wrenches from various manufacturers.
gpsman
> If I were truly getting anywhere from 100 to 300 when my
> click wrench says 200, then there is no way we could have zeroed in on
> certain specific numbers that prove to work best time after time after
> time.
(I thought you were having some sort of "problem".)
Generally, I think, a condition of "over torque" might be expected to
produce a satisfactory result in many if not most "normal" instances.
> Why would we see bolts fail at a fairly consistant number that
> is well below the upper range of a 50% error?
You're using bolts of inferior grade for your application?
> I'll bet I could
> consistantly snap the bolts at less than 10% above what we use as our
> max number.
Whatever you do, don't trot out to the bolts acting all crazy and
confirm your assumption.
I'm no engineer, but 10% seems to me as if you may be using the wrong
grade bolt... depending, of course, on your application, which, in
this case, could scarcely be more vague..
> Finally, the torque values we use work for our application
> - and the bolt failure points are consistant - across multiple torque
> wrenches from various manufacturers.
Similar errors of tolerance might be expected to produce similar
results.
I have only the slightest of ideas of what you are expecting of a
bolt, but my gut feeling is it's too much, and, to answer the original
question, again, from which end you torque it isn't going to make any
appreciable difference.
-----
- gpsman
sato...@gmail.com
> On Jun 30, 4:09 pm, mike <yellowbird...@hotmail.com> wrote:
> >
> >
> >
> >
> >
> > > This question came up while working on a project this weekend and I'm
> > > looking for some input.
> >
> > > Let's say I've got a nut and bolt holding something together and I
> > > want it torqued at XXX inch-pounds. I can hold the nut with a standard
> > > wrench and use the torque wrench on the bolt, or I can hold the bolt
> > > with a standard wrench and use the torque wrench on the nut.
> >
> > > One of the guys I was working with said "When given the chance, you
> > > always torque the nut." When I asked why the answer was "Because
> > > that's what I've always been told." You know how *those* conversations
> > > go!
> >
> > > So what's the deal? Does it matter? And if so, why? Could it be
> > > different in different cases? And if so, why?
> >
> > > Thanks!
> >
> nut is equivalent to the braking effect of the underside of the bolt
> head
>
> Even if the material on the underside of the nut is not equivalent to
> the material on the underside of the bolt head?
This isn't true. In the switchboard building industry we often have very long bolts and the bolt friction against the bus causes the wrench to click before proper torque is given. We ALWAYS torque the nut side (both sides are silver plated copper so surface friction doesn't matter in this case.)
DerbyDad03
wrench now.
Uncle Monster
[8~{} Uncle Furry Monster
DerbyDad03
Cousin Not-Too-Tight-Please Monster
Tekkie®
--
Tekkie