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]

Hope your customers don't follow this newsgroup.

Dave

"Albert Allen" wrote in message
news:567CB82B6C6F7231918BFE8FA4E0B45B@in.WebX.maYIadrTaRb...
> 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]

I think that practical applications will probably give you the answer, think
of highly stressed examples with spasmodic and intermittent loads. Lets
think
square fishing rods and square street lamp poles then there's square tube
oil
rigs and the square prop shafts you see on some cars, square tripod stands
square OHV push rods and the real flash square tube mountain bikes. Hollow
square camshafts. I have no doubt that there are some real high tech high
strength applications out there using square tubes and made to outperform
round tubes. Fact is that square tubes are easy to cut and join and are
ideal for every day applications, including space frames. In my old
fashioned way I was lead to believe that lugged or braze welded joints were
stronger. But probably machine welded joints are pretty good with no need
for skilled labour. Can't remember the last time I saw square tree trunks.


--
Laurence,

Power is nothing without Control
---


"Sean Dotson" wrote in message
news:358289F1F04154D152A00BB8A1A4ABEB@in.WebX.maYIadrTaRb...
> 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]

My Honda 250R is square tube. But then why are tube frame cars never done in square?

--
Kent
Member of the Autodesk Discussion Forum Moderator Program


"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]

Fortunately Dave there is only one of these frames out there in the field
and the other is our demo cat. I don't see that there will be any
catastrophic failures even with the 4130 tube frame in production but for
only 100 pounds of weight savings I just don't think it's worth it to even
continue. As Quinn Z. knows our cats are probably the most abused in the
industry and have always held up to the abuse admirably so I think our
customer base is still secure


"David Radlin" wrote in message
news:E92AEEC21EBC36EE859420E7ED7B4819@in.WebX.maYIadrTaRb...
> Hope your customers don't follow this newsgroup.
>
> Dave

[Anonymous]

Yep, that's a big one to consider...

--
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:4F562EA6D9D0604A6ADA5EC694F266EE@in.WebX.maYIadrTaRb...
> 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...

[gnrnr]

Having done rallying over a number of years and during that I have been involved in the building of a couple of roll cages. Only simple cages (6 point) so no design work was ever done. We used the specifications for material outlined in the rule book and used the smallest size allowed for Mild Steel tubing and made it from Chromolly tubing. I have never seen a square rollcage in a vehicle. The only reasons that I can think of are:


1. Round tuning is easier to bend in multiple planes and forms for bending are readily available.

2. Square tubing has relatively sharp corners (compared to a round tube). Not good for a helmet if you contact one during a crash.

3. Circular form is more resistant to impact than square form, especially if you cannot control the angle of impact (just trying vainly to remember some uni stuff here, I might be confused with pressure though).



regards


Steve

[Anonymous]

I believe hydrogen embrittlement can be a problem when welding chrome-moly
steel. May want to rule out welding practices as a contributor to the
problem.

$.02

Russ
"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]

Tubes R' Us... Which is better depends on material selection,
anticipated loading, joints, finish, standards and any regulations that
may affect your designs. Round can be built lighter and stronger for a
price.

Square tube pro:
For smaller bolt-on subframes I prefer square tube. Short and stiff.
Easy fit and quick to weld. Fast wraps and gussets. Drill a hole, weld
in a bushing and your have a mounting point. Slightly larger weld area.
Easy to setup jigs.

Square tube con:
Limited sizes and thickness. Seamless is more so. Bending is bad. Severe
vibration problems with long unsupported structures. Nasty oil-can
effect with unequal tube sizing and poor planning. Problems with
decorative plating. Polishing is not fun.

Round tube pro:
All sizes all the time. Round tubes can easily be bent to fit. Bent
tubes (with internal mandrel) can be stronger than the parent tube. Few
limits on joint configurations. Tube diameter and thickness can be mixed
and matched with benefits. Easy to polish before fabrication. Impact
resistance. Can be built ridiculously light. Tapered, butted, and/or
flared tubes are semi-available.

Round tube con:
Time. Mitered joints add big hours. Wrapped joints and gussets take
longer to fabricate. Mounting points and methods take longer too. Design
critical.

4130 pro:
Thin-wall and high strength in one product. Easy to work. Welds
beautifully. Heat-treatable. Big selection of sizes and shapes. Not that
much more expensive.

4130 con:
Welding is critical. Low temp TIG is preferred. Higher temp welds
destroy the material. Normalization (in heavy jig) required for maximum
life and strength. Design critical, or you'll hear a 'tink'. Finite
lifespan.

Mild steel pro:
Cheap. MIG or stick weld with impunity. Doesn't really care what you do
with it. Cheap. Great for consumable structures.

Mild steel con:
Cheap. Thick and heavy to get somewhat similar strength of finished
structure.

Unlike most salespeople, race vehicles have a short violent lifespan.
You salesman only sees them for a few hours at a time and has no idea
what the logbook reports. They have "no problems" 'cause they have at
least three replacements waiting. If a racing tube structure survives a
whole season without crashing it can safely be retired to fuddy-duddy
racing or parade duty for a long time. Old racers make great toys.

Race car suspension components used to be built with 1018. Plenty
strong, fairly light, and by deforming it absorbed lots of energy on
impact instead of snapping. Lots of spares there too... -Bill


Albert Allen wrote:

> Pound for pound which is stronger for a vehicle frame,
> round or square tube?

> salesmen pointed out, "all the race cars use round tube
> frames and they have no problems"

[Anonymous]

I see square tree-trunks all the time; got some hold'n my fence up!
~Larry

"Laurence Yeandle" wrote in message
news:5443A58EFFEA479A1E51D6B831DE75BA@in.WebX.maYIadrTaRb...
> I think that practical applications will probably give you the answer,
think
> of highly stressed examples with spasmodic and intermittent loads. Lets
> think
> square fishing rods and square street lamp poles then there's square tube
> oil
> rigs and the square prop shafts you see on some cars, square tripod stands
> square OHV push rods and the real flash square tube mountain bikes. Hollow
> square camshafts. I have no doubt that there are some real high tech high
> strength applications out there using square tubes and made to outperform
> round tubes. Fact is that square tubes are easy to cut and join and are
> ideal for every day applications, including space frames. In my old
> fashioned way I was lead to believe that lugged or braze welded joints
were
> stronger. But probably machine welded joints are pretty good with no need
> for skilled labour. Can't remember the last time I saw square tree
trunks.
>
>
> --
> Laurence,
>
> Power is nothing without Control
> ---
>
>
> "Sean Dotson" wrote in message
> news:358289F1F04154D152A00BB8A1A4ABEB@in.WebX.maYIadrTaRb...
> > 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]

4130 Normalized, I presume, is great for racecars (very high strength to
weight ratio as compared to most mild steels) but it's springy and work
hardens, It should only be TIG welded and stress relieved any place it's
welded or bent. I wouldn't use it in your application. If you decide to
stick with round tubing use 1020 DOM. It is almost as strong as 4130 and
tuff as hell plus it can be welded with a MIG. Hope this helps.



Steve


"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]

Yeh that's right Larry, they were used extensively along borders of railways
to keep out the vermin and alike. Sadly there all gone and been replaced by
concrete posts and galvanized iron. Though some can still be seen used as
fences enclosing the locals gardens, must have been excess stock at the time


--
Laurence,

Power is nothing without Control
---


"Larry Caldwell" wrote in message
news:78BF1780435BB3F1D44638F75CAA0BEC@in.WebX.maYIadrTaRb...
> I see square tree-trunks all the time; got some hold'n my fence up!
> ~Larry
>
> "Laurence Yeandle" wrote in message
In my old
> > fashioned way I was lead to believe that lugged or braze welded joints
> were
> > stronger. But probably machine welded joints are pretty good with no
need
> > for skilled labour. Can't remember the last time I saw square tree
> trunks.
> >
> >
> > --
> > Laurence,

[Anonymous]

Poppy cock it aint ugly its fashion, I am sure you remember in your
early twenties Kent riding this stuff CF, fashion always repeats itself
every twenty years or so the early 80's saw a return of square tube in
frames even if under the seat and tank brought sadness to its owner where
only the exposed tubes were square! The 80's weren't the age I was imagining
you though 🙂

--
Laurence,

Power is nothing without Control
---


"Kent Keller" wrote in message
news:BB027062CAA5B5CF2BFE30272706BE9F@in.WebX.maYIadrTaRb...
> My Honda 250R is square tube. But then why are tube frame cars never
done in square?
>
> --
> Kent
> Member of the Autodesk Discussion Forum Moderator Program
>
>
> "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
>
>