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Posted by John Doe on April 1, 2008, 12:53 am
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The metal I'm most used to working with is the soft aluminum flat
bar from the local hardware Borg.
Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
aluminum. Make a U shape out of it. If that U shaped piece of
aluminum flat bar is turned upside down and the ends glued to a hard
surface, I know approximately how much weight I could put on it
before it buckled.
What would be the equivalent approximate thickness of 301/304
stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
help.
Thanks.
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Posted by Tim Wescott on April 1, 2008, 4:01 pm
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John Doe wrote:
> The metal I'm most used to working with is the soft aluminum flat
> bar from the local hardware Borg.
>
> Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
> aluminum. Make a U shape out of it. If that U shaped piece of
> aluminum flat bar is turned upside down and the ends glued to a hard
> surface, I know approximately how much weight I could put on it
> before it buckled.
>
> What would be the equivalent approximate thickness of 301/304
> stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
> help.
>
> Thanks.
That depends a lot on the details of how you're making the 'U'. If it's
really failing by buckling then chances are the important parameter is
the stiffness of the arms, not the actual yield strength of the
material. You'd probably find that a 3/4" diameter tube with the same
amount of aluminum as the arms of your 'U' is much stronger.
I suspect that going to stronger, but thinner, material won't buy you a
heck of a lot of strength in the finished part. Thinner material that's
formed into a channel, then bent into a 'U' may work, but you'd need
some sort of fancy mandrel to keep the channel open when you bent the 'U'.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
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Posted by Bob's my cat on April 1, 2008, 11:28 pm
Please log in for more thread options > The metal I'm most used to working with is the soft aluminum flat
> bar from the local hardware Borg.
>
> Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
> aluminum. Make a U shape out of it. If that U shaped piece of
> aluminum flat bar is turned upside down and the ends glued to a hard
> surface, I know approximately how much weight I could put on it
> before it buckled.
>
> What would be the equivalent approximate thickness of 301/304
> stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
> help.
>
> Thanks.
Assuming that you are working in the elastic range, Steel is roughly 3
times as stiff as aluminum, however, when you start reducing the
thickness, the strength in bending, and stiffness of the bar decreases
rapidly. like with the square of the thickness I think, e.g. bar half
as thick is one quarter as strong, with steel being about 3 times as
stiff, 1/16" SS will still not be as stiff as the 1/8 Al. so
somewhere between 1/16 and 1/8.
On the other hand if you are talking about the yield point, not
elastic deflection, then it gets trickier, 301 can be work hardened to
a much higher yield strength than your hardware store aluminum, but
you'd have to know how hard it is, still, I'm not sure it is going to
have much more than three times the yield strength. maybe 4x but I'm
not sure. so the thickness guess above still applies.
Also steel is about three times as dense, and while plain low carbon
steel is much cheaper (by weight) than Al. I don't know that SS is, so
your SS part, while slightly thinner will be heavier and probably more
expensive.
Jay
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Posted by Joseph Gwinn on April 2, 2008, 9:34 am
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> > The metal I'm most used to working with is the soft aluminum flat
> > bar from the local hardware Borg.
> >
> > Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
> > aluminum. Make a U shape out of it. If that U shaped piece of
> > aluminum flat bar is turned upside down and the ends glued to a hard
> > surface, I know approximately how much weight I could put on it
> > before it buckled.
Glued? The glue joint will break first, I would think. I'm not sure I
visualize the setup.
> > What would be the equivalent approximate thickness of 301/304
> > stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
> > help.
> >
> > Thanks.
>
> Assuming that you are working in the elastic range, Steel is roughly 3
> times as stiff as aluminum, however, when you start reducing the
> thickness, the strength in bending, and stiffness of the bar decreases
> rapidly. like with the square of the thickness I think, e.g. bar half
> as thick is one quarter as strong, with steel being about 3 times as
> stiff, 1/16" SS will still not be as stiff as the 1/8 Al. so
> somewhere between 1/16 and 1/8.
By "strength" it sounds like you are talking about rigidity (stiffness),
which varies as the cube (not the square) of the thickness in the
dimension being bent, and linearly with the modulus of elasticity of the
material.
The modulus of elasticity of steel is about three times that of aluminum
alloys, and probably four times that of borg extrusions.
> On the other hand if you are talking about the yield point, not
> elastic deflection, then it gets trickier, 301 can be work hardened to
> a much higher yield strength than your hardware store aluminum, but
> you'd have to know how hard it is, still, I'm not sure it is going to
> have much more than three times the yield strength. maybe 4x but I'm
> not sure. so the thickness guess above still applies.
> Also steel is about three times as dense, and while plain low carbon
> steel is much cheaper (by weight) than Al. I don't know that SS is, so
> your SS part, while slightly thinner will be heavier and probably more
> expensive.
Borg metal will be far softer than say 6061 alloy.
I don't know that I would worry about elasticity before I figured out
the load capacity of the glued joint. From the above description, it
sounds like the ends are making epoxy butt joints to perpendicular flat
plates. Even if the metal is strong enough, the bays will deflect,
prying at the glue joints. The leverage is quite large, far exceeding
the strength of any available epoxy.
What is meant by "buckle"? Deflect visibly, or completely collapse,
dropping the load onto the floor? What is the application here?
Joe Gwinn
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Posted by John Doe on April 3, 2008, 12:22 am
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Thanks for the information.
> I don't know that I would worry about elasticity before I figured
> out the load capacity of the glued joint. From the above
> description, it sounds like the ends are making epoxy butt joints
> to perpendicular flat plates. Even if the metal is strong enough,
> the bays will deflect, prying at the glue joints. The leverage is
> quite large, far exceeding the strength of any available epoxy.
Sorry for not being explicit... my meaning of "glued" was "it's not
going anywhere".
> What is meant by "buckle"? Deflect visibly, or completely
> collapse, dropping the load onto the floor?
Less than permanently deforming. Being able to absorb shock without
moving/deflecting would be nice, but I suppose that's not possible.
> What is the application here?
Hopefully, whatever the material ends up being, it will support
Delrin rods under my skate frame as stopgaps in between the wheels.
Whatever the impact, the ends of the upside down U will be prevented
from moving outwards.
Sorry if I'm not specific enough, but that's because designs here
change from day to day. Sometimes I have to start the project before
the design is complete because the design part is so much fun and
otherwise the building part would never happen.
>
> Joe Gwinn
>
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> bar from the local hardware Borg.
>
> Using a 1/8" (thick) x 3/4" (wide) x 3" (long) piece of that soft
> aluminum. Make a U shape out of it. If that U shaped piece of
> aluminum flat bar is turned upside down and the ends glued to a hard
> surface, I know approximately how much weight I could put on it
> before it buckled.
>
> What would be the equivalent approximate thickness of 301/304
> stainless steel to 1/8" thick soft aluminum flat bar? Any idea will
> help.
>
> Thanks.