Which steel rod would have the least sag/twist/flex of a 4' stretch

[Jman]

I need a steel rod/s. precision ground, polished, turned, heat treated
whatever is most effective. 3/8" OD and a length of 4'. I need to know
what kind of steel (1144, Stressproff, 4140 TGPHT would have the least
amount of sagging, twisting, and flexing (wasn't sure on the scientific
terms for these). Can you help me out with that one? Or maybe point me
to a graph or an equation to work it out?

Thanks in advance for your time,

Jeremy

p.s in the future I will need an eight or 10 foot rod



--
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[Ed Huntress]

On Sun, 19 Apr 2015 23:18:02 +0000, Jman
<0f8503901d844703...@example.com> wrote:

>I need a steel rod/s. precision ground, polished, turned, heat treated
>whatever is most effective. 3/8" OD and a length of 4'. I need to know
>what kind of steel (1144, Stressproff, 4140 TGPHT would have the least
>amount of sagging, twisting, and flexing (wasn't sure on the scientific
>terms for these). Can you help me out with that one? Or maybe point me
>to a graph or an equation to work it out?
>
>Thanks in advance for your time,
>
>Jeremy
>
>p.s in the future I will need an eight or 10 foot rod

All grades will be the same (except for stainless, which will sag,
etc. slightly more). All hardness conditions will be the same.

I know this is hard to believe. When the second or third poster chimes
in, you'll start to believe it.

--
Ed Huntress

[Richard]

correct.

Fairly understandable essay on deflection of beams.


http://en.wikipedia.org/wiki/Deflection_%28engineering%29

[dca...@krl.org]

On Sunday, April 19, 2015 at 7:18:05 PM UTC-4, Jman wrote:
> I need a steel rod/s. precision ground, polished, turned, heat treated
> whatever is most effective. 3/8" OD and a length of 4'. I need to know
> what kind of steel (1144, Stressproff, 4140 TGPHT would have the least
> amount of sagging, twisting, and flexing (wasn't sure on the scientific
> terms for these). Can you help me out with that one? Or maybe point me
> to a graph or an equation to work it out?
>
> Thanks in advance for your time,
>
> Jeremy
>
>

Is the sagging only from the weight oft the rod? If so you can do a little better using a tube. Increasing the diameter will reduce the amount of sagging, and again using a tube will help even more. And decreasing the length will also help.

Dan

[Larry Jaques]

On Sun, 19 Apr 2015 23:18:02 +0000, Jman
<0f8503901d844703...@example.com> wrote:

>I need a steel rod/s. precision ground, polished, turned, heat treated
>whatever is most effective. 3/8" OD and a length of 4'. I need to know
>what kind of steel (1144, Stressproff, 4140 TGPHT would have the least
>amount of sagging, twisting, and flexing (wasn't sure on the scientific
>terms for these). Can you help me out with that one? Or maybe point me
>to a graph or an equation to work it out?
>
>Thanks in advance for your time,
>
>Jeremy
>
>p.s in the future I will need an eight or 10 foot rod

With no more than 0.0003" sag, right? <g>

Maybe something like this is in your future:
http://tinyurl.com/k89zupx Support that puppy!

--
"I believe there are more instances of the abridgment of the freedom
of the people by gradual and silent encroachments of those in power
than by violent and sudden usurpations."
--James Madison, Virginia Convention, June 16, 1788

[jon_banquer]

Knowing something about what it's going to be used for might help.

[Ignoramus25660]

Can you explain why it is so?

[Aristatos]

replying to dca...@krl.org , Aristatos wrote:

> dcaster wrote:
>
> Is the sagging only from the weight oft the rod? If so you can do a little
better using a tube. Increasing the diameter will reduce the amount of
sagging, and again using a tube will help even more. And decreasing the
length will also help.
> Dan

The sagging could be from a weight of 50 pounds to 100 pounds, twisting
would be from high torque stepper motors

thanks again people, just slightly confusing with the different numbers
and what not. And I should have specified the sagging from load, not
length.

thanks again, I was worried no one would answer, new here.

thanks

[Aristatos]

replying to Jman, Aristatos wrote:

> Jman wrote:
>
> I need a steel rod/s. precision ground, polished, turned, heat treated
whatever
> is most effective. 3/8" OD and a length of 4'. I need to know what kind of
> steel (1144, Stressproff, 4140 TGPHT would have the least amount of
sagging,
> twisting, and flexing (wasn't sure on the scientific terms for these). Can
you
> help me out with that one? Or maybe point me to a graph or an equation to
work
> it out?
> Thanks in advance for your time,
> Jeremy
> p.s in the future I will need an eight or 10 foot rod

The sagging could be from a weight of 50 pounds to 100 pounds, twisting
would be
from high torque stepper motors

thanks again people, just slightly confusing with the different numbers
and what
not. And I should have specified the sagging from load, not length.

thanks again, I was worried no one would answer, new here.

thanks

[Carl Ijames]

"Ignoramus25660" wrote in message
news:w_OdnY-49-ZH56nI...@giganews.com...

===================================================================

Iggy, the physical property that defines "stiffness" is called Young's
Modulus, or the modulus of elasticity. Pretty much all steel alloys have a
modulus between 28,500,000 psi and 30,500,000 psi, a range of 7%, so for
most calculation purposes "all" steel is basically 29,000,000 psi and
equivalent as far as stiffness goes. This does not change with heat treat
or hardness or work hardening or tensile strength or yield strength.
Similarly "all" aluminum alloys are 10,600,000 psi. Cast iron is about
10,000,000 psi for plain grey iron and up to about 15,000,000 psi for
nodular iron; that is one of the few materials whose modulus changes
significantly with minor changes in composition and heat treat. In terms of
shape, the stiffness is proportional to the fourth power of the lateral
dimension so 3/4" rod is 16 times stiffer than 3/8" rod, and pound for pound
thinwall large od tube is much stiffer than solid rod (of course, diameter
for diameter solid rod is stiffer than tube). For the OP, 4' or 3/8" rod
held parallel to the ground by supporting the ends is going to sag a good
bit under its own weight. The shape parameter that determines stiffness is
the moment of inertia (not the same rotational moment as for a spinning
object). For example, for 3/8" solid rod the moment if inertia I is
0.0009707 in^4, and 4' of 3/8" mild steel will weigh about 1.5 lbs. If you
support the ends by just sitting them on supports (as opposed to clamping
them so they can't pivot), and distribute that weight uniformly along the
length, the center will sag down 0.0767" and the maximum stress (based on
other calculations that vary with shape) will be 1740 psi, compared to a
yield strength of what, 40-50,000 psi so it is in no danger of permanently
bending. If you double the diameter the moment of inertia goes up by 16
(2^4) so it is 16 times stiffer, but the weight goes up by 4 (2^2) so the
net is one fourth the deflection (deflection is proportional to load/moment
of inertia if you keep the length constant) or 0.0192". The maximum stress
will be 870 psi. You can look up the moment of inertia for structural
shapes like rod, tubes, angles, I beams, and plug those numbers in, but for
each change of shape or dimension the maximum stress will have to be
recalculated from scratch if that is a concern (I'm too sleepy to take care
of stress and beam length, sorry). Usually it turns out that the deflection
is the limiting spec and by the time you get a design that keeps that down
below some limit you have such a strong structure that the yield rating is
overkill (like here).

As always, the program I recommend for quickie calculations like this is
engineering power tools, from www.pwr-tools.com. The freeware version will
do all of this with no time limit or ads, and the full version is only about
$50 and well worth it if you do a good bit of design.

-----
Regards,
Carl Ijames carl.ijames aat deletethis verizon dott net

[Lloyd E. Sponenburgh]

"Carl Ijames" <carl.i...@XXverizon.net> fired this volley in
news:mh285...@news4.newsguy.com:

>
> Iggy, the physical property that defines "stiffness" is called Young's
> Modulus, or the modulus of elasticity.

Bravo, Carl! A good, short treatise!

Lloyd

[Ed Huntress]

What Carl said. If you mean what is the physics behind it, no, you'd
have to look that up.

--
Ed Huntress

[Jim Wilkins]

"Aristatos" <0f8503901d844703ee...@example.com> wrote
in message
news:26eb9$55348c0a$43de0cc0$30...@news.flashnewsgroups.com...

In the first graph here the nearly vertical line is where the metal
will return to its original shape after being deflected. The slope of
the line is the deflection (strain) vs applied force (stress), or
stiffness.
http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=217&pageid=2144417131

Stronger or harder alloys simply follow the same line further up
before permanently deforming, at the point where the lines turn toward
horizontal. This is why greater strength or hardness doesn't provide
greater stiffness.

The second graph shows the difference between aluminum and steel of
identical cross-section (not weight).

You can demonstrate the bending behavior of steel by clamping two long
hardened drywall screws upright by the tip in a bench vise. Heat one
to redness with a propane torch to anneal it soft, then after it cools
push sideways on both. For a small force they both deflect
identically. As you push harder the annealed one will suddenly bend
when it reaches its "yield point" while the hard one remains springy.

-jsw

[Jim Wilkins]

"Jim Wilkins" <murat...@gmail.com> wrote in message
news:mh2no3$n1s$1...@dont-email.me...

> Stronger or harder alloys simply follow the same line further up
> before permanently deforming, at the point where the lines turn
> toward horizontal. This is why greater strength or hardness doesn't
> provide greater stiffness.
>

The Wiki describes elastic behavior in more detail, with examples:
http://en.wikipedia.org/wiki/Young%27s_modulus

It doesn't mention that the values are the force per unit area
required to stretch the sample by 100%, or to twice its length, which
can't be done in practice since it would break or become thinner,
decreasing the area.
http://en.wikipedia.org/wiki/Talk%3AYoung's_modulus
"it may be better to leave it out, to avoid confusing people, or at
least putting it down the bottom in some sort of "vaguely interesting
but complicated stuff" section, well away from the main definitons."

Some common materials like Tungsten are stiffer than steel, but also
heavier so they'd sag about the same if held horizontally. Beryllium
would be a great structural material if it wasn't poisonous.

You could try gently and unobstrusively bending a 3/8" steel rod in a
hardware store to get a hands-on feel for how stiff steel is, and
isn't.

-jsw

[Ed Huntress]

Coat hangers are good for that, too. They're what I use to demonstrate
the principle to people. When you're talking about how even the
crappiest steel has the same elastic properties as, say, 200,000
psi-yield music wire of the same diameter, it makes a good demo. Steel
doesn't come much crappier than coat hangers.

--
Ed Huntress

[Jim Wilkins]

"Ed Huntress" <hunt...@optonline.net> wrote in message
news:u74ajat4cnobj6r9p...@4ax.com...

How did you do it?

I usually had a bench vise and drywall screws available in the labs
where I worked. My demo was less convincing in someone's office with
only paper clips and a lighter, though they are enough to show how
fire severely weakens steel.

-jsw

[Ed Huntress]

On Mon, 20 Apr 2015 12:45:03 -0400, "Jim Wilkins"

If I'm in my shop, I take a 1-foot length of coat-hanger wire and
round spring wire (I always have lots of music wire around) and clamp
them with a scrap of wood between them, horizontally, in my vise, so
most of the foot of material is hanging out and there's maybe a 1-inch
gap between the two wires.

I wrap a few wraps of string around the outer tip of each, so the
weights won't slip off. Then I tie foot-long pieces of string at the
tips, and tie fishing sinkers to the ends of the string. A couple of
4- or 5-ounce sinkers, IIRC, will show equal bends. Then I lift up on
the sinkers to let the wires spring back.

Then I load on more sinkers until I get a permanent bend in the
coat-hanger wire. The demo shows the equal deflection (close, anyway)
within the elastic limit, and then what "elastic limit" means.

--
Ed Huntress

[Carl Ijames]

"Carl Ijames" wrote in message news:mh285...@news4.newsguy.com...

==================================================================

One quick addendum now that I'm more awake, it seemed odd that the variation
of I with lateral dimension was the fourth power, not third, so I double
checked and yes, with solid round rod I varies as diameter^4 but for
rectangular cross sections, like turning down an edge on a piece of sheet
metal or using angles for stiffening, I varies as the cube of the height.
For tubing it varies with the wall thickness vs. diameter but it seems to be
between ^3 and ^4 of the diameter.

[mog...@hotmail.com]

Coat hangers are also good for replacing 9 wire as drop-in light supports to Hilti straps (for drop ceilings).

[Aristatos/Jman]

replying to Ed Huntress , Aristatos/Jman wrote:

> huntres23 wrote:
>
> On Mon, 20 Apr 2015 10:42:34 -0400, "Jim Wilkins"

> Coat hangers are good for that, too. They're what I use to demonstrate
> the principle to people. When you're talking about how even the
> crappiest steel has the same elastic properties as, say, 200,000
> psi-yield music wire of the same diameter, it makes a good demo. Steel
> doesn't come much crappier than coat hangers.
> --
> Ed Huntress

Thanks again everyone, the answers are all really appreciated, and I think
I understand, but just in case;

If I understand what has been said it does not matter if it is 1144
Stressproof or 4140, it is going to sag under its own weight if it is 3/8"
X 4'. The treatment to the steel or the carbon percentage is only going
to affect how far it can bend or twist while still being able to return
to its original shape or before it will snap. Am I correct in my thinking
on this? I haven't checked out all of the links that were provided, but I
guess I could find a formula to see how much the sag will be at the center?

Would it be the same with a chromium vanadium steel alloy, or something
like that?

Thanks again everyone


ATTN ADMIN: I posted the first message under Jman before I created this
account, so I didnt know if you wanted to change the author on that post.
Great site

[et...@whidbey.com]

Like Ed said, the type and hardness has virtually no difference in
stiffness. So any steel of any hardness will sag the same amount. I
know, it seems like that can't possibly be true because heat treated
steel is used all the time when mild steel won't work because it is
too weak. But as long as the elastic limit is not reached all steels
will deflect almost exactly the same amount when the same amount of
force is put on these steels. This doesn't mean the steel has to snap,
as you put it, it just means permamanently deformed, in other words
the steel stays at least a little bent when the elastic limit is
surpassed. Tensile strength and yield strength will of course vary
tremendously from the weakest to the strongest steels while stiffness
will only vary a tiny amount. Go figger.
Eric

[Ed Huntress]

On Mon, 20 Apr 2015 19:18:02 +0000, Aristatos/Jman
<0f8503901d844703...@example.com> wrote:

>replying to Ed Huntress , Aristatos/Jman wrote:
>> huntres23 wrote:
>>
>> On Mon, 20 Apr 2015 10:42:34 -0400, "Jim Wilkins"
>> Coat hangers are good for that, too. They're what I use to demonstrate
>> the principle to people. When you're talking about how even the
>> crappiest steel has the same elastic properties as, say, 200,000
>> psi-yield music wire of the same diameter, it makes a good demo. Steel
>> doesn't come much crappier than coat hangers.
>> --
>> Ed Huntress
>
>
>
>
>Thanks again everyone, the answers are all really appreciated, and I think
>I understand, but just in case;
>
>If I understand what has been said it does not matter if it is 1144
>Stressproof or 4140, it is going to sag under its own weight if it is 3/8"
>X 4'. The treatment to the steel or the carbon percentage is only going
>to affect how far it can bend or twist while still being able to return
>to its original shape or before it will snap. Am I correct in my thinking
>on this?

You got it! And a lot faster than most people get that point. It's
kind of counter-intuitive.

>I haven't checked out all of the links that were provided, but I
>guess I could find a formula to see how much the sag will be at the center?

There are several people here who are good at that sort of thing.
You'll get some help.

>
>Would it be the same with a chromium vanadium steel alloy, or something
>like that?

Very close. As Carl said, the various alloys of steel are very close
in terms of Young's modulus, which is the value you're dealing with.

>
>Thanks again everyone

You're quite welcome.

[Spehro Pefhany]

On Mon, 20 Apr 2015 12:45:03 -0400, "Jim Wilkins"

http://i.imgur.com/GCfVh1F.jpg

--sp

[jon_banquer]

On Monday, April 20, 2015 at 12:18:04 PM UTC-7, Aristatos/Jman wrote:

> ATTN ADMIN: I posted the first message under Jman before I created this
> account, so I didnt know if you wanted to change the author on that post.
> Great site

Your using a web based front end to Usenet. Time to figure out what Usenet is and how it works.

[Jim Wilkins]

"Aristatos/Jman" <0f8503901d844703...@example.com> wrote
in message
news:12c80$553550ea$43de0cc0$29...@news.flashnewsgroups.com...

> replying to Ed Huntress , Aristatos/Jman wrote:
>> huntres23 wrote:
>
> Thanks again everyone, the answers are all really appreciated, and I
> think
> I understand, but just in case;
>
> If I understand what has been said it does not matter if it is 1144
> Stressproof or 4140, it is going to sag under its own weight if it
> is 3/8"
> X 4'. The treatment to the steel or the carbon percentage is only
> going
> to affect how far it can bend or twist while still being able to
> return
> to its original shape or before it will snap. Am I correct in my
> thinking
> on this? I haven't checked out all of the links that were provided,
> but I
> guess I could find a formula to see how much the sag will be at the
> center?
>
> Would it be the same with a chromium vanadium steel alloy, or
> something
> like that?
>
> Thanks again everyone

You can buy a 24" length of hardened steel as a "bell hanger" drill
bit to experiment with and confirm that you are applying the formulas
correctly.
http://www.homedepot.com/p/DEWALT-3-8-in-x-24-in-Bell-Hanger-Bit-DW1780/203314945

-jsw

[Jim Wilkins]

"Spehro Pefhany" <spef...@interlogDOTyou.knowwhat> wrote in message
news:jbrajatgrhbf9763r...@4ax.com...

Straight from the horse's mouth.

[Tim Wescott]

AFAIK the physics behind it is that the Young's modulus is about how the
atoms interact wherever they may be in the crystals, and the ultimate
strength is about how readily the individual crystals (or perhaps planes
within the crystals) can slip -- and carbon atoms tend to "pin" the
crystals (or crystal planes -- see how little I know?) to one another.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

[Tim Wescott]

On Mon, 20 Apr 2015 19:18:02 +0000, Aristatos/Jman wrote:

> replying to Ed Huntress , Aristatos/Jman wrote:

<< snip >>

(Everything everyone else said about material properties was accurate: I
can't add to it)

> ATTN ADMIN: I posted the first message under Jman before I created this
> account, so I didnt know if you wanted to change the author on that
> post. Great site

I'm not sure what site you're posting through, but this is an unmoderated
USENET newsgroup, so there's no administrator in the web forum sense.
Moreover, if I'm correct your posts are now distributed around on multiple
servers, so there's no way to unsay anything.

The lack of moderators is why you see so much political crap on this
group, unless your site has really good spam filtering.

[jon_banquer]

Why are you not sure? It's very clear where he's posting from:

[Ed Huntress]

Thank you, Tim. That's a *big* help. <g>

As for strength, yes, you're on the right track. The martensitic
crystal phase creates a pre-strain between the crystals, and that
keeps them from slipping as easily.

But I have no clue about stiffness. It's something going on deeper
than any materials discussion I've read, or that I recall, anyway. I
read a ton of this stuff when I was materials editor at American
Machinist, but that was 34 years ago.

--
Ed Huntress

[Ecnerwal]

On Sun, 19 Apr 2015 23:18:02 +0000, Jman
<0f8503901d844703...@example.com> wrote:
>
>I need a steel rod/s. precision ground, polished, turned, heat
>treated whatever is most effective. 3/8" OD and a length of 4'. I
>need to know what kind of steel

Well, I can't help thinking that what the OP really needs here is very
high carbon steel - so high carbon it's not got any iron and is not, in
fact, steel, but rather, carbon fiber, which is quite stiff, as
materials we actually have available go.

And/or a much larger diameter rod, which may require a better design of
whatever this is - certainly if going to 10 feet I don't think there's
*any* 3/8" rod that will even resemble "stiff" unless there's also a
robust frame and the rod can be put under great tension.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

[rangerssuck]

Those bits also have a convenient hole from which to hang your test weights. But, are they really hardened for their full length? Most drill bits are not hard at the chuck end, so that the chuck jaws can get some bite.

[Jim Wilkins]

"rangerssuck" <range...@gmail.com> wrote in message
news:101060ec-af91-4e52...@googlegroups.com...

A file will show the difference.

-jsw

[magne...@gmail.com]

Awesome clarification. Thank you.

[SCORELINK Limited]

Hi Carl!

Wow, great information -- I'm a biologist so this engineering is fascinating but elusive to me!

We have a similar problem, and I was wondering if you could lend your expertise:

We have a 1inch tube (25.4x3mm) at 3000mm length. It currently "sags" and we need to improve its rigidity. We can changer the diameter if needed, but I'm looking for a steer on what would be the best way to ensure high levels of rigidity over that distance, either tube or rod. any thoughts?

Many thanks in advance

[Jim Wilkins]

"SCORELINK Limited" wrote in message
news:71c61302-f83d-4fc0...@googlegroups.com...

-------------------------

All types of steel regardless of hardness have the same elastic constant, so
changing the material won't help. A thicker wall will increase stiffness
somewhat, but the best simple answer is likely to be increasing the
diameter. Since your length is more than 8' I suggest 1-1/2" or 2" by 10'
EMT electrical conduit (from a big box hardware store) if you can tolerate
the diameter. The trade size is a nominal value related to water pipe,
actual dimensions are different. You can attach to it with hanger hardware
or perforated pipe strap.

The Area Moment of Inertia is a measure of stiffness, to compare different
geometries or calculate the sag from loads.
https://www.engineersedge.com/calculators/section_square_case_12.htm

Notice that stiffness increases as the fourth power of diameter, while area,
weight and cost increase as the square.

[Jim Wilkins]

"Jim Wilkins" wrote in message news:uksrg6$1aull$1...@dont-email.me...

"SCORELINK Limited" wrote in message
news:71c61302-f83d-4fc0...@googlegroups.com...

-----------------------

Oh, you are in Britain. The same reasoning applies for whatever you have
easily available for larger diameter steel tubing. In the USA electrical
conduit and chain link fence posts are cheaper than water pipe of the same
nominal size because they have thinner walls, and may be suitable for
structural use. I'm not a mechanical engineer and can't figure the safe
loading for you.

[Clare Snyder]

1 inch X5/16 wall DOM tubing would be one of the best solutions if
you need to stay with one inch. 1 inch by 1/4 wall 4130 electric
welded tubing will likely be about the same price - trading off mild
steel for alloy vd the extra cost of mandrel drawn (which you don't
need the bore accuracy of). - or if you can go larger go to 1 1/2
inch 4130 or 1 1/4 inch DOM. Tubing has better bens strength than bar
stock and weighs a bit less - contributing less to the sag - - -

[Jim Wilkins]

"Clare Snyder" wrote in message
news:v2f4nil9vgrlaneqn...@4ax.com...

----------------------------

That's another good approach depending on your size versus cost constraints.
The thicker wall increases bending stiffness, the more expensive chrome-moly
4130 gives a higher overload safety factor though it bends the same as mild
steel of the same dimensions.

A possible problem with non-stocked, special-ordered material is that you
may have to pay for an entire standard length plus a cutting fee or spend
time searching for remnants. My stock of 1" 4142 solid rod was a specialty
metal supplier's leftover remnant and the discounted price was still $100,
about 10 years ago. It rusts readily in humid areas, which is why I
suggested galvanized tubing.

Aluminized steel or stainless car exhaust pipe from a custom fabricator may
be the quickest and easiest to find.

[Richard Smith]

As Jim and others say:
number-one approach - increase the diameter.

I'll add a complimentary comment.
Does the section have to resist local buckling?
This is a crucial issue in engineering.
Sometimes with something like an aeroplane weight it crucial and you
have to accept structures where if they buckle "that's it" - they are
finished.
For buildings and static steel structures you aften ensure that the
sections will keep "distributed" bending and will never buckle.

You will have to look-up about this.
For commercial steel sections it's the "Class" of a section.

[Jim Wilkins]

"Richard Smith" wrote in message news:lyzfyi7...@void.com...

-------------------------------------

That's a good point. As you increase the diameter and decrease the wall
thickness of tube to increase stiffness without raising cost/weight too much
the wall becomes vulnerable to indenting and buckling (sudden collapse) from
concentrated stress of a load hanger, especially if it makes only point or
line contact at the top. A strap reduces the concentration and a rigid pipe
hanger that keeps the side walls from bulging is even better. The end
supports are less of an issue because there's no bending stress there. The
ends can even be flattened and drilled for a bolt.

Buckling failure is different from tension or compression failure where the
metal's strength is exceeded. Buckling depends on its stiffness, resistance
to bending, and becomes more likely as unsupported length increases. A
wooden meter stick is easy to bend by hand though a short section of it
isn't. A good example of the failure is a beer can that is very strong when
filled because the internal pressure resists denting. When empty it's still
fairly strong unless dented, then hand pressure can crush it flat.

Commercial tubes meant for structural strength, such as chain link fence
posts, have a wall thickness around 1 to 1.5mm which resists accidental
dents but allows intentional bending. I didn't mention fence posts because
in the USA the commonly available ones are less than 3 meters long.
Thin-walled electrical conduit is similar and sold in 10 foot lengths. Fence
posts have the same outer diameter as water pipe, conduit the same inner
diameter which means that their fittings and rigid hangers are different.
Some combinations telescope together. Car exhaust tubing has similar walls
and is sized in even fractions of an inch in the USA while water pipe, fence
posts and conduit aren't, neither inch nor metric in the smaller sizes.

Yesterday I machined custom stainless flange repair fittings for exhaust
tubing that measured 1.997", though it was original equipment on a vehicle
made in Japan. The original (plain steel?) flange that connects the engine
outlet to the converter had rusted completely off, leaving only the fillet
weld which must have been stainless like the tube. I made a stainless two
piece split flange that fit snugly upstream of the fillet and a solid flange
to back up the graphite donut gasket below the fillet. Nuts on the spring
bolts tightened the solid flange against the gasket and slightly opened the
joint where the tubes contacted, allowing the springs to seal the gasket.

The exhaust leak past the unseated gasket had been very easy to find because
it dripped and sprayed condensed water after a cold start. At first the
gasket had appeared to seat from a tight fit on the tube but heat and
pressure moved it until the tubes touched instead. I didn't know what to
look for at first because I thought that area was all stainless and good for
life. I had replaced the catcon only because its rear flange had rusted away
enough to allow a leak.

In college while under-aged we "allowed" cider to ferment naturally.