Can I convert the degrees to foot pounds so I can use a torque wrench
to make them more exact?
Is there an abbreviation for "foot pounds"?
"Kenn E. Thompson" <webm...@deltafarms.com> wrote in message
news:96aa2d22.04112...@posting.google.com...
Bob Swinney
"Tom Gardner" <tom(nospam)@ohiobrush.com> wrote in message
news:DnRpd.209$nE7...@newssvr17.news.prodigy.com...
No -- that would be making them *less* exact.
Do you have an old school protractor? (The D-shaped thing with
angles marked on it in degrees.) Use your torque wrench as instructed
to tighten to 30 foot pounds, and then place the protractor to measure
the angle of the wrench handle. Turn it an extra 45 degrees (1/8 of a
full turn). This part is to stretch the bolt after you get it to that
torque starting point. And that bolt should *never* be re-used -- you
stretch it once, no more.
>Is there an abbreviation for "foot pounds"?
"Ft-Lbs" is one.
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
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--- Black Holes are where God is dividing by zero ---
They are not wanting a specific 'torque' on the bolt, they want a
specific amount of bolt stretch, or yield. You torque it to 30 to get it
to the initial point, then they want it stretched by x mm, which is 1/8
of the pitch. So say for a M8x1.5 this is going to be .1875 mm of
stretch, after the 30 lb-ft of torque are applied. As I believe Don said,
NEVER, NEVER reuse a torque+stretch bolt. They are designed to stretch
ONCE. They WILL FAIL if stretched a second time.
And yes, technically, it is lb-ft, not ft-lbs.
--
Anthony
You can't 'idiot proof' anything....every time you try, they just make
better idiots.
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You are far better off simply doing as they say.
I was amazed when I started looking at tightening techniques. I have
an industrial fastener reference from a largish nuts and bolts firm
here in Oz. In it they say that "guess work" by the operator is on
average 35% inaccurate and that's plus or minus!....and the torque
wrench is 25% ! Turn of nut (your need) is 15%. So actually, guessing
is less harmful over torque wrenches than torque wrenches over turn of
nut! <G>
Then you get down to really careful, $$ stuff like strain gauges,
special washers that show tension etc. Lastly are Strain Gauges, which
these guys say are within 1%.
3 * 4 = 4 * 3. ;^)
Tim
--
"I've got more trophies than Wayne Gretsky and the Pope combined!"
- Homer Simpson
Website @ http://webpages.charter.net/dawill/tmoranwms
Also...
Doesn't this assume that these bolts are tightened past their elastic limit?
Past their UTS?
Surely not...
==
Jeff R.
> Doesn't this assume that these bolts are tightened past their elastic limit?
> Past their UTS?
Brain fart.
I meant "Yield Stress"
(oops)
The tightening technique is to get the bolt very near the yield point,
and not over it. However, if you reuse the bolt, you will exceed the yeld
point. This will result in insufficient clamping pressure for the joint,
and could (very likely, actually) result in broken fastners.
The torque technique is becoming industry standard nowadays, and that is
because it is inherintly more accurate.
If you torque a bolt to 70-80 lb-ft, the inaccuracies of the measurement
grow expotentially as you increase torque due to friction, head galling,
lubrication distribution and other variables during the tightening. By
keeping the measured torque lower, you reduce these inaccuracies
substantially. By specifying the angle of final placement from a lower
given torque, you use the thread pitch to determine the linear stretch
amount for the fastener.
I'm well aware of the dot vs. cross product, but didn't know the order of
the units mattered at all... interesting!
Now if only I would remember that bit of trivia. ;-p
Mathematically they don't matter -- and if you depend on convention then
you'll just get screwed up by the person who's document you're reading
who didn't know the convention.
Best to understand what you're looking at, and assume that the
manufacturer _probably_ knew what they were talking about.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
remove ns from my header address to reply via email
>The tightening technique is to get the bolt very near the yield point,
>and not over it. However, if you reuse the bolt, you will exceed the yeld
>point. This will result in insufficient clamping pressure for the joint,
>and could (very likely, actually) result in broken fastners.
AFAICS, you shouldn't exceed the yield point if you use the bolt
again. The whole idea of Yield point (and I am prepared to learn
another lack in my "knowledge base here, believe me" is that it's the
point at which the steel deforms permanently. Any bolt tightened to
below the yield will return to its former length. (???)
I can see two possible problems. Metal fatigue if the bolt is in place
for an extended time, and / oe under heat/cold/ vibration etc.
Accidental overtightening. Thsi would be an enginerring tning. If the
bolts were _really_ taken to near yield, there would little margin for
error. But once a bolt has exceeded yield, it starts to lose tension
anyway. That woud be dangerous.
remove ns from my header address to reply via email
>
AFACUI, the answer is still no if you are asking about stretching. A
spring is the most dramatic example of a metal that can be "stretched"
without exceeding yield stress. To stretch steel you need to apply
stress. It will start to stretch under very small stress. It will
_permanently_ stretch when it passes yield.
remove ns from my header address to reply via email
>This part is to stretch the bolt after you get it to that
>torque starting point. And that bolt should *never* be re-used -- you
>stretch it once, no more.
Ok. Why should yopu not re-use the bolt? You are only stretching it,
but not to Yield.
I have questioned Anthony about this. My theory says I am right, but
you guys know your stuff. So fact is against me. I am never willing to
let being thought a fool stop me from opening my mouth. I have leraned
a lot that way...
...everything except when to keep my mouth shut! <G>
Metal fatigue plays a factor once the bolt is stretched. I know that there
are a number of engines that use this method in tightening head bolts. And
they are not to be re-used under any circumstances.
Lane
>On 26 Nov 2004 21:54:28 -0500, dnic...@d-and-d.com (DoN. Nichols)
>vaguely proposed a theory
>......and in reply I say!:
>
> remove ns from my header address to reply via email
>
>>This part is to stretch the bolt after you get it to that
>>torque starting point. And that bolt should *never* be re-used -- you
>>stretch it once, no more.
>
>Ok. Why should yopu not re-use the bolt? You are only stretching it,
>but not to Yield.
I think it's because they get hot while under tension and while
getting hammered by the engine. That gives 'em a small amount of work
hardening that won't like a restretch later on.
I read it somewhere on the internet, but then again, I read it
somewhere on the internet.
>I have questioned Anthony about this. My theory says I am right, but
>you guys know your stuff. So fact is against me. I am never willing to
>let being thought a fool stop me from opening my mouth. I have leraned
>a lot that way...
>
>...everything except when to keep my mouth shut! <G>
--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/
But without more information, I can't tell you if these bolts are
being tightned until they yield or not. You can design bolted joints
so that the bolts are tightened unitl they yield slightly, or you can
design joints so they do not tighten the bolts to yield.
But if the original poster has the book that says how to tighten the
bolts, I am pretty sure it would say if the bolts should not be
reused. My SWAG would be that tightening them 45 degrees, probably is
not into yield. On the other hand, using new bolts ( of the correct
grade )will never get you into trouble.
Dan
Old Nick <nsnsa...@dodo.com.au> wrote in message news:<fmuhq011g31431kq6...@4ax.com>...
> Ok. Why should yopu not re-use the bolt? You are only stretching it,
Ideally, this is true. i.e. Yield point is stress level that separates
elastic (returns to original dimention when the stress is relieved) from
plastic (returns to original dimention when the stress is relieved)
deformation. Regretably most materials do not behave ideally so you
will often see yield point defined as the point where residual
deformation is some small percentage of original dimension.
Ted
How can you possibly correlate degrees to Ft lbs ? If I torque a 1/4 20..
45 degrees that will be much more torque then torque in a 1/4 28... 45
degrees.
If the manual says torque then turn ...it's already calculated on a fresh
bolt ... however if you reuse a standard bolt it has already been stretched
once ,I would not want to stretch it again.
remove ns from my header address to reply via email
>Ideally, this is true. i.e. Yield point is stress level that separates
>elastic (returns to original dimention when the stress is relieved) from
>plastic (returns to original dimention when the stress is relieved)
I am sorry. I am a bit confused by the above lines.
>deformation. Regretably most materials do not behave ideally so you
>will often see yield point defined as the point where residual
>deformation is some small percentage of original dimension.
Which is to say that you use a bolt that only _just_ doesn't really do
the job. <G>
The concept behind stress to yield bolts is to get a very consistent
bolt to bolt torque value when tightened according to the listed
procedure. Many modern head bolts have a reduced diameter section
on the shank for this purpose. Torque variance can be as small as
1% using this method. Ordinary torque wrench methods give a
bolt to bolt consistency variance that is often as large as 20%.
Consistent torque reduces the tendency of aluminum heads to
warp.
Gary
>
> How can you possibly correlate degrees to Ft lbs ? If I torque a 1/4 20..
> 45 degrees that will be much more torque then torque in a 1/4 28... 45
> degrees.
> If the manual says torque then turn ...it's already calculated on a fresh
> bolt ... however if you reuse a standard bolt it has already been stretched
> once ,I would not want to stretch it again.
I don't think I said anything about correlating degrees to ft lbs.
But if you have say a 4 inch long 1/4 20 bolt and you tighten it so it
is snug and then tighten it 45 degrees, you will have stretched the
bolt 0.0125 inches. So for a 4 inch long bolt you would have
stretched it .0031 inches per inch of length.
Now assuming this is less than yield, you can loosen it and retighten
it over and over. No new bolt needed. You don't worry about flexing
the springs in your car, do you. Stretching less than yield means it
returns to the original length when the stress is removed.
If you use a different length bolt, or a bolt with different threads
per inch, you have to calculate how many degrees to tighten it for the
stain you want.
Dan
Dan
The name of the thread is convert degrees to Foot Pounds so I assumed that's
what the subject was ... happens all the time where a thread starts out one
thing and turns into something else.
I guess you have to go back to the original post to figure out where the
subjects at ... I don't because some of the threads are really long.
*You* didn't -- but it is in the "Subject: " header from the
original question.
>But if you have say a 4 inch long 1/4 20 bolt and you tighten it so it
>is snug and then tighten it 45 degrees, you will have stretched the
>bolt 0.0125 inches. So for a 4 inch long bolt you would have
>stretched it .0031 inches per inch of length.
And to calculate the equivalent foot-pounds figure, you would
need to know the diameter of the section being stretched, the length of
the reduced diameter or section being stretched, and the tensile
strength at the current temper of the material. (And, as has already
been discussed, trying to do it all with a torque wrench is less
accurate.
>Now assuming this is less than yield, you can loosen it and retighten
>it over and over. No new bolt needed. You don't worry about flexing
>the springs in your car, do you. Stretching less than yield means it
>returns to the original length when the stress is removed.
>
>If you use a different length bolt, or a bolt with different threads
>per inch, you have to calculate how many degrees to tighten it for the
>stain you want.
*Or* -- a different reduced diameter length, if present. And
that would be more likely to be a torque to yield bolt application.
Enjoy,
DoN.
--
Email: <dnic...@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
The turn-of-nut method sets a fixed stretch in the bolt, which gives a
fixed clamping pressure on the parts.
Depending on the design, the bolt is either acting like a spring, and:
modulus*(cross section)*stretch/(unstrained length of the stretched
section)
gives the clamping pressure
or it it being stretched to yeild and:
(yeild strength)*(cross section of yeild zone)
gives clamping pressure
In either case, the bolt should not be reused. If it is TTY, the next
time it is pulled in, the previously yeilded portion will have been
reduced in cross section and yeild at a lower tension. If not TTY, the
original tension is likely calculated to be 80% or more of yeild, and
there are likely high stress points that will yeild either as the bolt
is pulled in or during service.
The bolts are also quite likely to break, as the closer to the yeild
they are brought, the fewer fatigue cycles they can take, the obvious
limit being one cycle when they are stressed to the ultimate strength
the first pull (<--simplification to reduce volume of text)
The initial torque is principally to insure the parts are seated
properly before stretching the bolt. Since you arn't measuring the
actual stretch dirctly, there is no other easy way to insure that the
1/8 turn is used entirely for stretch, rather than some being wasted
to draw the parts together. The actual tension will be the sum of that
produced by the stretch of the bolt from the 1/8 turn and the tension
from the initial torque (which also strethes the bolt, and is likely a
minor part of the final tension)
There neatest tension setting setup I have worked with uses bolts
that have a small hole bored part-way up the axis with a pin slightly
longer than the hole depth inserted. As the bolt is tensioned, it
stretches, and when the pin is flush, the stretch, and therefore the
bolt tension, is correct.
remove ns from my header address to reply via email
>Now assuming this is less than yield, you can loosen it and retighten
>it over and over. No new bolt needed. You don't worry about flexing
>the springs in your car, do you. Stretching less than yield means it
>returns to the original length when the stress is removed.
This was my argument. But it would seem that in the real world, that
stretched bolt has been "damaged", or is assumed to be damaged.
Minimalism in engineering, heat, vibration etc.
remove ns from my header address to reply via email
>webm...@deltafarms.com (Kenn E. Thompson) wrote in message news:<96aa2d22.04112...@posting.google.com>...
>> Working on a Deutz Diesel engine. The instructions say to torque the
>> bolts to 30 foot pounds then turn 45 degrees.
>>
>> Can I convert the degrees to foot pounds so I can use a torque wrench
>> to make them more exact?
>>
>
>The turn-of-nut method sets a fixed stretch in the bolt, which gives a
>fixed clamping pressure on the parts.
>
>Depending on the design, the bolt is either acting like a spring, and:
>modulus*(cross section)*stretch/(unstrained length of the stretched
>section)
>gives the clamping pressure
>
>or it it being stretched to yeild and:
>(yeild strength)*(cross section of yeild zone)
>gives clamping pressure
But surely if it's stretched to Yield (_and beyond_ if it's deformed),
then the clamping pressure will sart to drop straight away. Unless you
got _exactly_, and I mean _exactly_, Yield, you would not get (yeild
strength)*(cross section of yeild zone) but some lesser figure.
But I do have to admit,,,snip of very useful stuff after that. <G>
Amazingly, you just about do get exact clamping pressure. In fact, if
you don't go far into yeild, the pressure goes UP slightly as yeild
goes on a) because the yeild isn't an exact point, as the material
begins to stretch and neck, the stress goes up slightly, compensating
to a good extent for the reduced cross sectional area, and b) as the
material yeilds, it work hardens slightly, increasing the yeild stress
slightly. Ya, the effects are closely related. In practice, if it is
dead critical, a tool is used to detect yeild and stop there.
> Working on a Deutz Diesel engine. The instructions say to torque the
> bolts to 30 foot pounds then turn 45 degrees.
>
> Can I convert the degrees to foot pounds so I can use a torque wrench
> to make them more exact?
There's no really practical way other than doing it as specified.
"Angle-to-torque" conversion would involve too many things that could be
variable - What's the pitch of the thread on the bolt? What's the
coefficient of friction for the material the bolt is made from? How
about for the material that the bolt is going into? What's the
shape/area of the bolt-head to fastened surface contact point, as well
as the CoF for that interface? How many tuyrns of thread are going to be
in the hole and meshed with the threads that are in the hole? Etc, etc,
etc... LOTS of "etc"s that add up to "You're better off doing it as the
instructions say."
Add in the fact that, as others have said, these are probably "stretch
bolts", intended to be cranked to a specific torque as a "reference
point", then cranked an extra 1/8th of a turn in order to put a
specified amount of stretch on them, and you're still ending up back at
"do it the way the instructions say."
Besides - 45 degrees = 1/8 of a turn - It's really not that difficult to
"eyeball" a well-within-reasonably-accurate approximation.
--
Don Bruder - dak...@sonic.net - New Email policy in effect as of Feb. 21, 2004.
Short form: I'm trashing EVERY E-mail that doesn't contain a password in the
subject unless it comes from a "whitelisted" (pre-approved by me) address.
See <http://www.sonic.net/~dakidd/main/contact.html> for full details.
remove ns from my header address to reply via email
hmmm...OK. If that is the way it's worked, then I can see why you
would not use the bolt again.
I couldn't see why you would want to go to, and beyond Yield, when you
would get an elastic stress there to clamp the joint, without needing
to wreck the bolt. But if there is a point when you can actually
maximise the clamp even aftger Yield then I can see the reason. As a
RAG (Rough As Guts) "engineer" I just use a bigger bolt! <G>
Thanks.
Even standard bolts generally shouldn't be reused in high stress
applications like an engine head because the properties change when
they are first torqued.
Typical designs for load-bearing bolts loaded in the elastic range are
50 to 80 percent of the yeild stress. All you get for using a bigger
bolt and not loading it to this high a stress is a bigger hole and a
more expensive bolt. Greater than 80 percent gets into the range where
unknowns in the installation process may bring the bolt into yeild.
Often not a good thing, as bolts not designed for this usually don't
have good yeild characteristics (they tend to yeild at the thread
root, where the minimum diameter is. bold designed for TTY usually are
reduced shank diameter)
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