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

"SCORELINK Limited" wrote in message
news:71c61302-f83d-4fc0-bcf9-3e8b68ad1832n@googlegroups.com...

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

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

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

"SCORELINK Limited" wrote in message
news:71c61302-f83d-4fc0-bcf9-3e8b68ad1832n@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.

On Thu, 7 Dec 2023 04:08:04 -0800 (PST), SCORELINK Limited
<info@scorelink.io> wrote:

>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
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 - - -

"Clare Snyder" wrote in message
news:v2f4nil9vgrlaneqnh0gnj2q13m963nc26@4ax.com...

On Thu, 7 Dec 2023 04:08:04 -0800 (PST), SCORELINK Limited
<info@scorelink.io> wrote:

>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
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 - - -

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

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.

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.

"Richard Smith" wrote in message news:lyzfyi7du4.fsf@void.com...

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.
-------------------------------------

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.