On Monday, April 20, 2015 at 10:49:22 AM UTC-4, Ed Huntress wrote in rec.crafts.metalworking:
On Mon, 20 Apr 2015 10:42:34 -0400, "Jim Wilkins"
> wrote in rec.crafts.metalworking:
>
> >> "Aristatos"
> >>> reply> >>>> Jman wrote in rec.crafts.metalworking:
> >>>>
> >>>> 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
> >
> >> 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:
> >
formatting link
> >
> >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.
> >
formatting link
'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.
>
> 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.
Coat hangers are also good for replacing 9 wire as drop-in light supports to Hilti straps (for drop ceilings).