which aluminum to use for clamp?

What aluminum alloy has the least bendability? I am designing a clamp for my device and looking for aluminum with least bendability.

Why aluminum? It is softer and has more friction than steel which is better for clamping.

Thanks, Alex

Reply to
Alex
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I'd suggest 7075-T6.

Harold

Reply to
Harold & Susan Vordos

Is it castable?

Reply to
Alex

6082 is used widely,or Aluminium-Bronze?
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Reply to
wws

If that's the only criteria, have you considered separate aluminum clamp pads?

Regards, Michael

Reply to
DeepDiver

Then why not screw an aluminium pad to a steel clamp like soft jaws in a vice? It won't matter what grade you use then because it won't be taking the load.

Dave Baker - Puma Race Engines

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"How's life Norm?" "Not for the squeamish, Coach" (Cheers, 1982)

Reply to
Dave Baker

7075 is what I would use. The alum pad on steel body is a good idea, a bit extra work. It depends on how animal you will be when torqueing things down. Also how thick and long the clamps need or can be. Generally, if you are using less than a cheater bar, the 7075 should be quite adequate.

michael

Reply to
michael

356 is the quinticential(sp) aluminum casting alloy. It seems to prefer breakage to much bending, but it's pretty strong before it yields. Remember to make it much thicker than a steel clamp. :)

Tim

-- In the immortal words of Ned Flanders: "No foot longs!" Website @

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Reply to
Tim Williams

Define 'bendabilty'. It is important to note that all the aluminum alloys have essentially the same modulus of elasticity, or stiffness. Some alloys have much higher ultimate tensile strengths though, so they will deflect farther without permanent deformation. For the same weight an aluminum structure can be stiffer than one made of steel, but it will be larger. Then there are the fabrication issues. Some aluminums can be cast, but not extruded. The ones that extrude well mostly weld well also. Most of the strong alloys don't weld, or form well, so machining is about your only option.

I worked with a young engineer who designed a C-clamp shaped punch frame from aluminum. When it flexed too much he went off trying to find a 'stronger' aluminum alloy. It was fun to watch him learn the basics all over again. Stronger aluminum alloys aren't stiffer, neither are stronger steel alloys.

Gary H. Lucas

Reply to
Gary H. Lucas

put aluminum shims under the steel pads. This is a common practice with four jaw chucks and castings. The aluminum deforms enough to get a good grip on the casting and the hard jaws.

John

Reply to
John

Please clear up one thing: What do you mean by "bendability"? If you mean yield strength, several people have mentioned 7075-T6, which is relatively strong. But if you mean something like stiffness -- the ability to avoid springing under stress -- then all aluminum grades are pretty close in value. And they're all about 1/3 as resistant to springing as steel is.

If you need something stiff, then the suggestion that you use steel and affix aluminum pads will meet your needs with a lot less mass than something made of all-aluminum. You can get the same resistance to spring-like deflection by using thicker aluminum, however.

Ed Huntress

Reply to
Ed Huntress

Be careful about assuming that softer automatically means more friction. There are LOTS of factors that determine what real friction will be between any two pieces of metal. One of them, of course, is the material you're trying to clamp. Aluminum on aluminum is pretty sticky; but metals like brass and bronze, which are quite soft, have relatively low coefficients of friction even when sliding on harder materials, like steel. And, some machine tool builders successfully use aluminum gibs on box-way type machines. There must be a reason for that.

What aluminum does most often in clamping applications (normally as a pad or buffer under the toe of a steel clamp) is deform and compress under pressure. This can accomplish several things: It can protect the workpiece from being damaged by the clamp. Or, it sometimes allows the rough surface of a workpiece (like a sand-casting, or something rough milled) to bite into the aluminum. When that happens, the clamp's ability to resist sliding or shifting of the work will result from the shear strength of the bumps and divots where clamp and workpiece are enganged, and will have very little to do with friction. This works extremely well in many cases; but only when clamping forces are high enough to cause engagement between the metals. Also, the deformation of an aluminum clamp pad, even against a smooth workpiece, can cause the clamping force to be spread out over a larger surface area. A larger area means that more clamping force can be applied before the workpiece is dented or scarred.

Usually, when an aluminum pad is placed between the work and a steel clamp, that allows and requires HIGHER clamping forces, and therefore a stronger clamp. If the aluminum pad is going to work by compression, deformation, spreading out forces, or by wrapping itself around the inpefections in the workpiece surface, then it has to be squeezed hard enough for all that to happen. If clamping forces are too small to do the necessary squeezing, then the soft pad might be squeezed instead by cutting forces. The result of that, usually, is that a workpiece will come loose during machining. Bad news.

Others in the group have suggested aluminum pads or points on steel clamps. In my experience, that's an excellent way to go. Unless you have VERY good control over clamping forces (which means there's not a chance in hell that an operator will ever get near the clamp with any kind of hand tool), then you can be absolutely certain that the strength of your clamps WILL be tested to the limits. Even good quality forged steel clamps routinely get bent or broken. To start out with a clamp design that's not fit to survive a nuclear attack, at least, is usually just a plan to have problems, and to make the clamps out of something stronger before the job is nearly finished.

Good luck!

KG

Alex wrote: > What aluminum alloy has the least bendability? > I am designing a clamp for my device and looking for aluminum with least > bendability. >

Reply to
Kirk Gordon

As Gary and Ed have described - basically aluminum will deflect 3 times as much as steel when under the same conditions i.e.; same shape, same load, same length. Doesn't matter what type of aluminum or what type of steel.

Reply to
tomcas

So why don't they make many springs out of aluminum ;-) (He said rhetorically.)

Tim

-- In the immortal words of Ned Flanders: "No foot longs!" Website @

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Reply to
Tim Williams

Materials with a low modulus of elasticity, like aluminum, deflect only a small amount before deforming permanently. A spring can be made from aluminum, and if operated within the right range of motion it could last a long time. Compared to a steel spring with the same ratings it would be absolutely huge.

Springs are one of those devices that seem to always get used in ways that completely violate good engineering practices. Over compression and over extension are big problems. I use gas springs quite a lot because the performance in long stroke applications is so much more linear. Of course a long stroke gas spring only goes about 250,00 cycles.

Gary H. Lucas

Reply to
Gary H. Lucas

Absolutely true. On several occasions I've had designs questioned by people who've had bad experiences with poorly applied springs because "springs are unreliable and break". My standard response is to point out how many cycles the valve springs in an IC engine are subjected to.

Which reminds me of the moron at a design review who complained that my proposal was no good because cams don't work!

Ned Simmons

Reply to
Ned Simmons

If Gary's comment about fatigue limits wasn't clear (it was rigorously correct, but it comes out sounding the opposite of what it means ), there is no minimum load below which aluminum will not fatigue and crack. I hope it's less confusing stated that way.

Aluminum works as a spring as long as the loads are so low, and/or the number of cycles it goes through in a lifetime is so small, that you never encounter its fatigue limits. That's almost certainly the case with small-aircraft landing gear. The number of cycles it will go through in a lifetime is trivial compared to, say, an automobile engine valve spring.

Steel, on the other hand, has a load threshold, BELOW WHICH it will never, in practical terms, fail from fatigue. It's a basic property that distinguishes the two materials for mechanical applications.

BTW, if you exceed that threshold for steel, it, too, will eventually fail from fatigue. The number of required cycles is fairly well defined, at least as an order of magnitude, as long as the cycles are consistent.

Ed Huntress

Reply to
Ed Huntress

Is that what the modulus means? I presumed it was about the general stiffness/flexibility (within elastic limits) of the material.

Yup. And it also will fail from fatigue. And hence my use of "he said rhetorically". :)

BTW I picked up a piece of silver solder at the welding store, MAN is that stuff springy!

Tim

-- In the immortal words of Ned Flanders: "No foot longs!" Website @

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Reply to
Tim Williams

I haven't been following the thread, but responded specifically to the statement that they don't make springs out of aluminum, which by itself isn't true. There is probably a good reason why Cessna's spring gear is made of steel. (grin) BTW, (more thread drift) Yaks have been using titanium spring gear legs for a long time, milled from solid, bent, and the halves welded together to make them hollow. The Yak 26 and 29, aerobatic light aircraft, are built that way I believe. Possibly another material that won't make "good" springs.

Reply to
Glen

Yak 55;

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love that airplane!)

I mentioned a Yak 26 and 29, I meant to say Sukoi;

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6 AM this morning I woke up remembering the erroneous Yak 26 & 29 post, BTW I'm pretty sure I saw a Sukoi 29 at Arlington with Yak 54 type gear, round tubular gear.
Reply to
Glen

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