round tube vs. square tube?

[Anonymous]

A simple yet complex question for all you P.E.'s or anyone else that want to
give it a stab..........Pound for pound which is stronger for a vehicle
frame, round or square tube?

Here is the situation:
We have always built square tube frames for our Sno-Cat's but recently have
been working with 4130 round tube frames. We are trying to get vehicle
weights down and although we have saved about 100 pounds using round tube
over square (no big deal on a 7300 pound machine) we have also added 16 man
hours per frame in the process and we are starting to see some slight joint
cracking in the round tube frames (which we have never had with square)

As you can tell I am biased toward the square tube frames but as one of our
salesmen pointed out, "all the race cars use round tube frames and they have
no problems"

Any advice would be greatly appreciated and pardon the non Inventor related
subject but this is where all the brains are

Thanks

[Anonymous]

Albert,
Just my thoughts:

There is no general "this better than that". Only case where clearly the
round is better than the square is torsion.

But you will have never torsion alone. All other cases, you have to
calculate or do an FEA analysis on every piece in question, to be very sure
that you come close to, but do not eceed the allowed stress and deflection.

It might be easier to make fine welding joints between square shapes than
between round ones, this might be the cause why some weld failed recently.
But again, there is no general rule that round tube weldments are worse than
square ones.

But well, if the salesman states something,... You might get a decent FEA
tool to do your job?

---
Regards,
---
Leo Laimer
Bad Ischl - Austria

[Anonymous]

I think Leo provided a pretty good answer. Too many variables to give a specific answer.

[Anonymous]

Albert,

How many hours do they put on race cars?... I don't think they race on the
North Slope, either.

4130 is good stuff, but only as good as the welds.Welds on Racecar frames
are inspected with a comparator (ask your machinest). NO undercut on a 4130
weld is too much.

Only 16 man hours?? are you sure? What about down the line in assembly and
even field mods?

Your salesman is smoking crack. Perhaps he would like to be the one to mount
"something" (storage box, hangar- anything) to a Cat in the field with a
drill and welder.

I have never ever seen in "real" applications round structual NOT crack.

The easiest way to explain to the salesman (he's in the bathroom getting a
hit) it take him out to the shop and grab a joint of 2x3x.125 rec tube off
the rack and toss it at him noting how "stiff" it is.

Then grab a joint of 3/4 Cold Roll shaft and toss it to him noting the
"spagetti" properties.

Then go back to work.

QBZ


"Albert Allen" wrote in message
news:FFDD17FA47507A26A21B3039689F73F7@in.WebX.maYIadrTaRb...
> A simple yet complex question for all you P.E.'s or anyone else that want
to
> give it a stab..........Pound for pound which is stronger for a vehicle
> frame, round or square tube?
>
> Here is the situation:
> We have always built square tube frames for our Sno-Cat's but recently
have
> been working with 4130 round tube frames. We are trying to get vehicle
> weights down and although we have saved about 100 pounds using round tube
> over square (no big deal on a 7300 pound machine) we have also added 16
man
> hours per frame in the process and we are starting to see some slight
joint
> cracking in the round tube frames (which we have never had with square)
>
> As you can tell I am biased toward the square tube frames but as one of
our
> salesmen pointed out, "all the race cars use round tube frames and they
have
> no problems"
>
> Any advice would be greatly appreciated and pardon the non Inventor
related
> subject but this is where all the brains are
>
> Thanks
>
>

[Anonymous]

If you're in the market for an inexpensive solution
try these guys

href="http://www.grapesoftware.mb.ca/">http://www.grapesoftware.mb.ca/

I used this at my last job because my boss was too
cheap to go for a real solution.  It's a little tough to use but will get
you there faster than hand calcs.

STAAD from Research engineers is another relatively
low priced beam analysis program to look at.

Either program will save you time and money vs.
build it and break it engineering.
--
Dave Burton
SICO Inc

http://www.sicoinc.com

style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">

"rllthomas" <
href="mailto:rllthomas@attbi.com">rllthomas@attbi.com> wrote in message

href="news:f151742.1@WebX.maYIadrTaRb">news:f151742.1@WebX.maYIadrTaRb...

I
think Leo provided a pretty good answer. Too many variables to give a specific
answer.

[Anonymous]

I have always been under the belief that to weld 4130 properly it has to be done with a
Tig. If they are using a Mig could that be the problem? I am not a welder so take it for
what its worth.

So Quinn ... are you saying if I make a Dunebuggy out of square tube of equal wall
thickness compared to a round tube frame it will be less likely to crack and be better in
the long run?

BTW I never saw a single crack on my 4130 car frame. I also have not found any cracks in
round tube dunebuggys??

--
Kent
Member of the Autodesk Discussion Forum Moderator Program


"Quinn Zander" wrote in message

> 4130 is good stuff, but only as good as the welds.Welds on Racecar frames
> are inspected with a comparator (ask your machinest). NO undercut on a 4130
> weld is too much.
>
> I have never ever seen in "real" applications round structual NOT crack.

[Anonymous]

...or try these guys...www.3dmet.com...

--
Mark A. Bystry
Engineer
Ziggity Systems, Inc.
mbystry@ziggity.com

[Anonymous]

Depends on which variables you hold constant (wall thickness or OD etc..)
but for 99% of applications a square tube with the same cross sectional area
(hence weight) as a square tube will have a higher moment of inertia value
and hence will be stiffer.

However the guys have brought up a lot of other points that need to be
considered as well.
--
Sean Dotson, PE
http://www.sdotson.com
Check the Inventor FAQ for most common questions
www.sdotson.com/faq.html
-----------------------------------------------------------------------
"Albert Allen" wrote in message
news:FFDD17FA47507A26A21B3039689F73F7@in.WebX.maYIadrTaRb...
> A simple yet complex question for all you P.E.'s or anyone else that want
to
> give it a stab..........Pound for pound which is stronger for a vehicle
> frame, round or square tube?
>
> Here is the situation:
> We have always built square tube frames for our Sno-Cat's but recently
have
> been working with 4130 round tube frames. We are trying to get vehicle
> weights down and although we have saved about 100 pounds using round tube
> over square (no big deal on a 7300 pound machine) we have also added 16
man
> hours per frame in the process and we are starting to see some slight
joint
> cracking in the round tube frames (which we have never had with square)
>
> As you can tell I am biased toward the square tube frames but as one of
our
> salesmen pointed out, "all the race cars use round tube frames and they
have
> no problems"
>
> Any advice would be greatly appreciated and pardon the non Inventor
related
> subject but this is where all the brains are
>
> Thanks
>
>

[Anonymous]

More than wall thickness needs to be considered...

e.g. for a round tube of OD 2" to be equal in area to a square tube of 2"
outside dim, the wall thickness of the round will be 0.125" while the square
will be 0.097 wall...and the square will be stiffer.

Turn the square on it's edge (to make a diamond shape and it will be stiffer
still. Of course it more difficult to design with it in that orientation
however (running crossbraces etc..)
--
Sean Dotson, PE
http://www.sdotson.com
Check the Inventor FAQ for most common questions
www.sdotson.com/faq.html
-----------------------------------------------------------------------
"Kent Keller" wrote in message
news:635E2493BD18CDBEF64B95B8869D30ED@in.WebX.maYIadrTaRb...
> I have always been under the belief that to weld 4130 properly it has to
be done with a
> Tig. If they are using a Mig could that be the problem? I am not a welder
so take it for
> what its worth.
>
> So Quinn ... are you saying if I make a Dunebuggy out of square tube of
equal wall
> thickness compared to a round tube frame it will be less likely to crack
and be better in
> the long run?
>
> BTW I never saw a single crack on my 4130 car frame. I also have not found
any cracks in
> round tube dunebuggys??
>
> --
> Kent
> Member of the Autodesk Discussion Forum Moderator Program
>
>
> "Quinn Zander" wrote in message
>
> > 4130 is good stuff, but only as good as the welds.Welds on Racecar
frames
> > are inspected with a comparator (ask your machinest). NO undercut on a
4130
> > weld is too much.
> >
> > I have never ever seen in "real" applications round structual NOT crack.
>
>

[Anonymous]

"a square tube with the same cross
sectional area as a square tube will have a higher moment
of inertia value and hence will be stiffer"

Can't let this one go... vbg

Dave

"Sean Dotson" <sean at sdotson dot com> wrote
in message
href="news:93B68028FC77B5F4DE6001F3FFE8FA8D@in.WebX.maYIadrTaRb">
face=Arial
size=2>news:93B68028F...
face=Arial size=2>...

> Depends on which
variables you hold constant (wall thickness or OD etc..)
> but for 99% of
applications a square tube with the same cross sectional area
> (hence
weight) as a square tube will have a higher moment of inertia value
> and
hence will be stiffer.
>
> However the guys have brought up a lot
of other points that need to be
> considered as well.
> --
>
Sean Dotson, PE
>
size=2>http://www.sdotson.com
> Check
the Inventor FAQ for most common questions
>
href="http://www.sdotson.com/faq.html">
size=2>www.sdotson.com/faq.html
>
-----------------------------------------------------------------------
>
"Albert Allen" <
size=2>albert@sno-cat.com> wrote in
message
>
href="news:FFDD17FA47507A26A21B3039689F73F7@in.WebX.maYIadrTaRb">
face=Arial
size=2>news:FFDD17FA4...
face=Arial size=2>...
> > A simple yet complex question for all you
P.E.'s or anyone else that want
> to
> > give it a
stab..........Pound for pound which is stronger for a vehicle
> >
frame, round or square tube?
> >
> > Here is the
situation:
> > We have always built square tube frames for our
Sno-Cat's but recently
> have
> > been working with 4130 round
tube frames. We are trying to get vehicle
> > weights down and although
we have saved about 100 pounds using round tube
> > over square (no big
deal on a 7300 pound machine) we have also added 16
> man
> >
hours per frame in the process and we are starting to see some slight
>
joint
> > cracking in the round tube frames (which we have never had
with square)
> >
> > As you can tell I am biased toward the
square tube frames but as one of
> our
> > salesmen pointed out,
"all the race cars use round tube frames and they
> have
> > no
problems"
> >
> > Any advice would be greatly appreciated and
pardon the non Inventor
> related
> > subject but this is where
all the brains are <g>
> >
> > Thanks
>
>
> >
>
>

[Anonymous]

Dang it.. and I was doing so good today...

"a *square* tube with the same cross sectional area as a *round* tube will
have a higher moment of inertia value and hence will be stiffer"

--
Sean Dotson, PE
http://www.sdotson.com
Check the Inventor FAQ for most common questions
www.sdotson.com/faq.html
-----------------------------------------------------------------------
"David Radlin" wrote in message
news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> "a square tube with the same cross sectional area as a square tube will
have a higher moment of inertia value and hence will be stiffer"
>
> Can't let this one go... vbg
>
> Dave

[Anonymous]

Actually, even this generalization can be proven invalid.

Dave

"Sean Dotson" wrote in message
news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> Dang it.. and I was doing so good today...
>
> "a *square* tube with the same cross sectional area as a *round* tube will
> have a higher moment of inertia value and hence will be stiffer"
>
> --
> Sean Dotson, PE
> http://www.sdotson.com
> Check the Inventor FAQ for most common questions
> www.sdotson.com/faq.html
> -----------------------------------------------------------------------
> "David Radlin" wrote in message
> news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > "a square tube with the same cross sectional area as a square tube will
> have a higher moment of inertia value and hence will be stiffer"
> >
> > Can't let this one go... vbg
> >
> > Dave
>
>

[Anonymous]

There is another thing to consider...a race car frame (at least most of
them) is made to collapse to absorb the energy of a crash. I see a race car
frame as being designed as close as possible to the failure point with
basically no safety margin. As far as why Quad bikes are not made with
square tube (a question that was also asked)....and I figure looks count for
a lot and a quad or motorcycle frame would be really ugly if made out of
square tube


"Sean Dotson" wrote in message
news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> Dang it.. and I was doing so good today...
>
> "a *square* tube with the same cross sectional area as a *round* tube will
> have a higher moment of inertia value and hence will be stiffer"
>
> --
> Sean Dotson, PE
> http://www.sdotson.com
> Check the Inventor FAQ for most common questions
> www.sdotson.com/faq.html
> -----------------------------------------------------------------------
> "David Radlin" wrote in message
> news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > "a square tube with the same cross sectional area as a square tube will
> have a higher moment of inertia value and hence will be stiffer"
> >
> > Can't let this one go... vbg
> >
> > Dave
>
>

[Anonymous]

Round or square is indifferent assuming manufacturability does not
compromise ones strength comparatively over another.

What's important here is that the applied loading be understood and
structure designed accordingly.

Dave

"Albert Allen" wrote in message
news:ECDBC52F359F6CA0AD8CB3D537623F81@in.WebX.maYIadrTaRb...
> There is another thing to consider...a race car frame (at least most of
> them) is made to collapse to absorb the energy of a crash. I see a race
car
> frame as being designed as close as possible to the failure point with
> basically no safety margin. As far as why Quad bikes are not made with
> square tube (a question that was also asked)....and I figure looks count
for
> a lot and a quad or motorcycle frame would be really ugly if made out of
> square tube
>
>
> "Sean Dotson" wrote in message
> news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> > Dang it.. and I was doing so good today...
> >
> > "a *square* tube with the same cross sectional area as a *round* tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> >
> > --
> > Sean Dotson, PE
> > http://www.sdotson.com
> > Check the Inventor FAQ for most common questions
> > www.sdotson.com/faq.html
> > -----------------------------------------------------------------------
> > "David Radlin" wrote in message
> > news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > > "a square tube with the same cross sectional area as a square tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> > >
> > > Can't let this one go... vbg
> > >
> > > Dave
> >
> >
>
>

[Anonymous]

Another consideration in the racing/industrial argument is that the
racecars/quads are rigid and are designed to stay rigid within the
"controlled" conditions (only one rider on a quad sticker)

I'm confident that your Cats will be grossly overloaded from time to time in
not only GVW but drawbar pull as well.

QBZ

Caterpillar D8N's loaded on their backs going to pull out 2 other D8N's that
fell into a bog hole-freakin' incredible-Just point (GPS) and drive>

"Albert Allen" wrote in message
news:ECDBC52F359F6CA0AD8CB3D537623F81@in.WebX.maYIadrTaRb...
> There is another thing to consider...a race car frame (at least most of
> them) is made to collapse to absorb the energy of a crash. I see a race
car
> frame as being designed as close as possible to the failure point with
> basically no safety margin. As far as why Quad bikes are not made with
> square tube (a question that was also asked)....and I figure looks count
for
> a lot and a quad or motorcycle frame would be really ugly if made out of
> square tube

[Anonymous]

That's why I said for 99% of applications (which you snipped out ). You
*can* make a round stronger but in the normal ratios of OD to wall diameters
you find in production tubing you will not likely come across one where the
inverse is true.

--
Sean Dotson, PE
http://www.sdotson.com
Check the Inventor FAQ for most common questions
www.sdotson.com/faq.html
-----------------------------------------------------------------------
"David Radlin" wrote in message
news:7EFD8F6A9FEA3FB33672CE79515F9B61@in.WebX.maYIadrTaRb...
> Actually, even this generalization can be proven invalid.
>
> Dave
>
> "Sean Dotson" wrote in message
> news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> > Dang it.. and I was doing so good today...
> >
> > "a *square* tube with the same cross sectional area as a *round* tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> >

[Anonymous]

I agree that if we had the time we could probably design a bullet proof
sno-cat frame out of 4130 but as the case is so much of the time, sales has
already sold these extra light cats and we have not been given the time to
perfect the design. I am just trying to get ammunition to stop the sale of
these "untested" round tube frames and continue to go with square until we
have more time to design,develop and test the 4130 frame.

Why will so much of the time management take the sales departments word over
the engineering departments word?.....yes I already know the answer

Thanks for all the response and I will be showing these to the boss.



"David Radlin" wrote in message
news:86FB8D56D387581F88C05499D3D6322E@in.WebX.maYIadrTaRb...
> Round or square is indifferent assuming manufacturability does not
> compromise ones strength comparatively over another.
>
> What's important here is that the applied loading be understood and
> structure designed accordingly.
>
> Dave
>
> "Albert Allen" wrote in message
> news:ECDBC52F359F6CA0AD8CB3D537623F81@in.WebX.maYIadrTaRb...
> > There is another thing to consider...a race car frame (at least most of
> > them) is made to collapse to absorb the energy of a crash. I see a race
> car
> > frame as being designed as close as possible to the failure point with
> > basically no safety margin. As far as why Quad bikes are not made with
> > square tube (a question that was also asked)....and I figure looks count
> for
> > a lot and a quad or motorcycle frame would be really ugly if made out of
> > square tube
> >
> >
> > "Sean Dotson" wrote in message
> > news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> > > Dang it.. and I was doing so good today...
> > >
> > > "a *square* tube with the same cross sectional area as a *round* tube
> will
> > > have a higher moment of inertia value and hence will be stiffer"
> > >
> > > --
> > > Sean Dotson, PE
> > > http://www.sdotson.com
> > > Check the Inventor FAQ for most common questions
> > > www.sdotson.com/faq.html
> >
> -----------------------------------------------------------------------
> > > "David Radlin" wrote in message
> > > news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > > > "a square tube with the same cross sectional area as a square tube
> will
> > > have a higher moment of inertia value and hence will be stiffer"
> > > >
> > > > Can't let this one go... vbg
> > > >
> > > > Dave
> > >
> > >
> >
> >
>
>

[Anonymous]

Stiffness and ease of manufacturing is why my friends mini bikes frames are
made of square tubing. Ugly, nah I have even seen some really high end
custom bikes from square tubing for many reasons and they were definitely
not ugly.

Cheers,
-Shaan

"Albert Allen" wrote in message
news:ECDBC52F359F6CA0AD8CB3D537623F81@in.WebX.maYIadrTaRb...
> There is another thing to consider...a race car frame (at least most of
> them) is made to collapse to absorb the energy of a crash. I see a race
car
> frame as being designed as close as possible to the failure point with
> basically no safety margin. As far as why Quad bikes are not made with
> square tube (a question that was also asked)....and I figure looks count
for
> a lot and a quad or motorcycle frame would be really ugly if made out of
> square tube
>
>
> "Sean Dotson" wrote in message
> news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> > Dang it.. and I was doing so good today...
> >
> > "a *square* tube with the same cross sectional area as a *round* tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> >
> > --
> > Sean Dotson, PE
> > http://www.sdotson.com
> > Check the Inventor FAQ for most common questions
> > www.sdotson.com/faq.html
> > -----------------------------------------------------------------------
> > "David Radlin" wrote in message
> > news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > > "a square tube with the same cross sectional area as a square tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> > >
> > > Can't let this one go... vbg
> > >
> > > Dave
> >
> >
>
>

[Anonymous]

Actually, Kawasaki and Yamaha have both used rect tubing on their motocross bikes and Hondas have rect alum frames now.

I would have to say that in the last decade a lot more effort has been given by the motorcycle manufacturers to understand the complex vehicle loading so that they can come up with an optimized solution. I'm sure CAD/FEA had nothing to do with it 🙂

Rich

[Anonymous]

If the tubing needs to be bent particularly in a non-planar fashion, then
round tubing would hold certain advantages in consideration of such.

Dave

"Albert Allen" wrote in message
news:ECDBC52F359F6CA0AD8CB3D537623F81@in.WebX.maYIadrTaRb...
> There is another thing to consider...a race car frame (at least most of
> them) is made to collapse to absorb the energy of a crash. I see a race
car
> frame as being designed as close as possible to the failure point with
> basically no safety margin. As far as why Quad bikes are not made with
> square tube (a question that was also asked)....and I figure looks count
for
> a lot and a quad or motorcycle frame would be really ugly if made out of
> square tube
>
>
> "Sean Dotson" wrote in message
> news:70958018ABF2C39D8445426380ECBA09@in.WebX.maYIadrTaRb...
> > Dang it.. and I was doing so good today...
> >
> > "a *square* tube with the same cross sectional area as a *round* tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> >
> > --
> > Sean Dotson, PE
> > http://www.sdotson.com
> > Check the Inventor FAQ for most common questions
> > www.sdotson.com/faq.html
> > -----------------------------------------------------------------------
> > "David Radlin" wrote in message
> > news:1E9B7C064132582876D02830CF77A711@in.WebX.maYIadrTaRb...
> > > "a square tube with the same cross sectional area as a square tube
will
> > have a higher moment of inertia value and hence will be stiffer"
> > >
> > > Can't let this one go... vbg
> > >
> > > Dave
> >
> >
>
>