# Bending 4mm dia stainless steel rod

• posted

Hello, can anybody tell me how much I can bend a 4mm dia 316 ss (or

304ss) rod in terms of bending radius? Is there a mathematical formula that gives the maximum bending radius as a function of material properties? Or where can I find the data for maximum bending radius for rods made of different materials?
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Maximum bending radius is infinite. That's the way you buy it - straight! :-)

Perhaps you mean minimum bending radius when bending cold?

GWE

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Grant, ever hear the term: "Bitch-Slap"?

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Sho did, homey!

GWE

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Missed the original post...just for the heck of it I tested on some .225" dia (5.7 mm dia) material I had laying around...Material harder than dead soft, probably a bit less than quarter hard.

"natural" bend radius (clamped in vice and just bent) was 7/16". Forced radius without special tooling was 3/16". I know that we've often put a true 90 degree inside bend on .307" (7.79 mm) dia T304 stainless rod and haven't seen cracking. Of course, not seeing cracking doesn't mean it wont show up under the right chemical conditions down the road.

Anyway, the point is, stainless is very ductile as long as you aren't starting out pre-work hardened. Tight bends should be no problem with 4 mm.

Koz

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LOL! That was a good answer!

Nick, wiping tears of laughter out of my eyes.

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Grant Erwin ha scritto:

Yes, obviously I meant the minimum bending radius.

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Sure. But Grant's answer was just to good! :-)

If you can't find it in any table, here is a coarse way to calculate it: You need the maximum elongation*) until the material breaks. Then you pick some radius, calculate the length of the arc in the inner side of the bend, calculate the length of the arc on the outer bend. If lengths differ more than the elongation, it will break.

There will be other effects, so you will get an even smaller radius without breaking. But I guess you come quite close.

*) With that I mean (don't know the technical term): If you stress metal, it will get -after a certain force- longer (and _not_ spring back). That value is in % and in the ballpark of 5..20%. You have to find it out for your material.

Nick

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Nick! That was as much of an epiphany as the time a guy explained gyroscopic precession to me in terms of orbital mechanics! Seriously... that makes it so SIMPLE! Thanks.

LLoyd

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So, come on. Out with it. How does precession work?

Expiring minds need to know.

Mark Rand RTFM

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Ok... I was afraid of this. It's SO easy to explain with "chalk talk", I forget how hard it is to describe without pictures.

Picture a gyroscope NOT as a disc rotating on a shaft, but as a SINGLE particle in orbit around a point. Basically, you're looking at one atom of the gyroscope's material. Every other atom will behave the same, so one does the trick for the explaination.

View the rotation from one edge of the orbit, with the "axle" perspective vertical through the center of the orbit.

For sake of the explaination, consider the orbit to be counter-clockwise -- NASCAR atoms.

Now allow the particle to orbit around until it's exactly in front of you -- between you and the "axle".

Summary so far -- vertical shaft, horizontal disk, rotation CCW, and we're considering the point on the periphery of the disc closest to our view. SNAPSHOT a velocity vector for the particle we're considering. It's moving left to right along a straight horizontal line (if the gyroscope were of infinite diameter)

Now apply a force upward on the particle in parallel to the axle, which attempts to rotate the whole affair along an axis horizontal to your view. What happens to the particle?

It was moving along a horizontal line. Now you've altered the vector to a "lower-left to upper-right" direction. Nothing else changes.

Switch your mental view back to the single-particle gyroscope now. If the orbit is now tilted lower-right to upper-left, then the whole disc of particles will have tilted UP at a point 90-degrees in rotation from the point of applied force to the disk.

LLoyd

What happens is you deflect it

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Elongation, elongation to fracture, elongation to break are all used. For austenitic stainless steels (300 series) it can be as high as 70%.

Ned Simmons

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That works for me. Thanks.

Mark Rand RTFM

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A long winded theory by an academic.

A practical observation by an engineer.

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