I purchased the below-picture 1/8" x 3" stock from onlinemetals.com and, after spending some time milling it to the precise size, realized that it's slighly bowed!! I don't have a feeling gauge, but I know the piece of paper that I can slip under it is 4thou.

Any suggestions on how to straighten this? I tried using my fixture plate + clamps to squeeze the bow out but didn't have any luck. I don't have a press brake either. Appreciate any thoughts. thanks!

Do you have any room to machine the thickness?

Fretsman - no, unfortunately i don't have any room in the thickness.

If I did, that would solve the problem, but i've got 4 pieces like this - and machining both sides of the four pieces on my TAIG would take quite a while!!

I see, unfortunately I'm no help then, sorry-

No need to apologize!

I tell you what I would do. Put it on an extremely hard and flat surface and smack it with a flat 1 pound hammer. Work over the bow and start by using modest hits with the hammer until you see improvement.

That's kind of why I was asking about the amount of material he may have but since there is none, I'm thinking that's out -

Are there any holes that are being machined into the stock. I'm thinking if you have a way to "Secure" the plate and pull it true, you would be able to complete the part.

If you don't mind, what shape of part are you making? Since is .125, if we know the outside dimensions, we may be able to help more.

I have a 1/4" plate that is the same way. I use it for perishable material though so I didn't care. If it is that critical that it be flat, I would contact them and let them know there is a problem and see if they will make it right.

I live a couple hundred miles away from them and pretty soon, I will make a road trip there to stock up. Let me know how they treat you if you contact them.

Why does it need to be so flat? What is the part being used for?

regards

You can't simply crush it flat it will spring, you have to bend it the other way, past it's elastic limit.

I'd put it down on a thick bar, shim under either side, narrow bar down the middle on the top then crush it with G clamps.

Look see if it was flatter, if not flatter repeat with thicker shims until it is.

Hitting it will probably make it bend in other ways and not fix anything.

Actually, Robin, you can peen material that is cupped on the concave side with short strong blows to bring it back as it relieves stress. We've done this with heat treated steels when we have something like 4340 that's oil quenched and goes nuts after heat treating.

Aluminum is pretty soft though so if these have to be "that" flat and have no room to remove material, I'd like to hear from others on some tricks because personally these would be scrap as after all this time it would be easier to just machine up 4 more blanks.

What is your tolerance, tikka?

You can bend something by peening if you have a wide support on the back and strike a narrow blow to expand the face you are hitting.

Wouldn't say it relieves stress though, just conterbalances it :confused:

Makes a mess of the surface in all.

Thanks for the thoughts, everyone.

The four pieces I'm struggling with are to be the four sides of a box. The "bottom" of the box is 0.25" and has no problems, which is great. But the bow in the four pieces mean the corners of the box have gaps which are not acceptable.

I tried "peeining" it for about 20 minutes last night and can't say I had any luck. I think the only way to fix it (at least with the tools available to me) is like Robin Hewitt said - shim it & "crush" with clamps...

I need to keep the 0.125" thickness due to drawing requirements.

Absolutely, Robin, and as for the stresses, it just always seemed like that what's going on in that situation (heat treat). They go in ground flat and come out looking like a cup, lol!

I need to keep the 0.125" thickness due to drawing requirements.


That's why I like to make parts first..... and then draw them up......I kid, of course - ;)

Fretsman: nothing wrong with that approach, as it yields known results....that's where experience comes into play. Alot of crap is "designed" nowadays, and the designer has never stepped onto the shop floor.

regards

you're not kidding, tru-er words were never spoken.......

On the show "How it's made" there was an episode about how safes are made and in one part of that subject (safes) a guy was using a hydraulic shaft to get the 1 inch thick very large plate to exact flatness using said hydraulic shaft...bite the bullet, by yourself a cheap hydraulic jack, and make a fixture/jig to hold your pieces and push it [hydraulically] to straight but first, view the episode to get an idea of how it was done. Dude, I would've ordered the pieces slightly larger then 1/8 (possibly 3/16 to a quarter inch in a very long one piece, enough to cut up to desired lengths after getting it to desired thickness, you do have a cnc equipped mill don't you? let the mill run to desired thickness, it won't hurt the machine, right?) if anything I stated doesn't help...bite the bullet and start all over...live and learn.

The only way you can realistically expect a flat part from thin material is to set an oversize piece in a low-temp solder, machine on side flat(something that is more difficult than you can imagine given a thin workpiece to begin with), then recast and mill the opposite side flat. My question is what are you making and what kind of flatness tolerances do you have to meet? Perfection is an illusion that we only think we can achieve. If you lack the ability to accurately measure the deviation, I question just how accurate you really need to be.

Scrapman - the other 3" x 1/8" 6061 Aluminum that I've purchased in my brief tenure as a hobbyist has not been bowed like this. Although I could re-mill it, I want to explore what my options are to salvage the existing pieces - and possibly even learn something new in the process. You're right - I don't own the appropriate tools to accurately measure this deviation - but I don't believe that says anything about my interest in making accurate work. It's the carpenter, not the tools. My flatness tolerances for this particular piece are "optical" - i.e. when you hold the piece against a flat-surface, naked human eye should not see a bow; I would estimate this to be about 1thou. Like I said, the other 3" x 1/8" stock has met this test. Clearly one lesson learned is to check your stock before investing time in it.

Please! No offense was intended. I'm a toolmaker by trade and was attempting to qualify the degree of accuracy you needed, and if you didn't need a high degree of flatness, is it really worth the effort. The aluminum is worth less than a buck, while your time is certainly worth many, many, many times that. It's always the little things that hang us up, isn't.

It's the thin stock in the picture correct?

Perhaps you could use a piece of welding rod or dowel rod in the center as a fulcrum, and use a series of clamps on both sides to bend it a bit. some thin stock could protect the good stuff.

Hello there. I am a metalworker/blacksmith/welder and this is an area I might be of assistance. First thing I would try is laying the metal on a smooth concrete floor bow up, place a 2x4 (long enough to use as a handle) on top, and have a buddy wail on it with a sledgehammer. Work from one end to the other for bar or center out for squares, rectangles, or circles. If still concave after that, try the same thing but on a piece of plywood (softer) outside in the dirt. That will allow more flex to counter the memory of the metal. You might even place the plywood over a shallow dent in the ground. Nothing is truly finished unless it has been beaten on with a hammer!

Another thing to try would be to anneal the metal by heating it up to a dull red and then letting it cool naturally (normalize), and then working. That allows the molecules to relax and spread out a little, and removes most of the memory effect also.

But REALLY what I would do depends on the construction of the box. If it is getting welded, I would just face the bows out and clamp it all closed and tack it. Done. (Be sure to put a bevel on the edge.) If it's bolted, same thing,
just invert and clamp it closed. Hope that helps!

First thing I would try is laying the metal on a smooth concrete floor bow up, place a 2x4 (long enough to use as a handle) on top, and have a buddy wail on it with a sledgehammer. Work from one end to the other for bar or center out for squares, rectangles, or circles. If still concave after that, try the same thing but on a piece of plywood (softer) outside in the dirt. That will allow more flex to counter the memory of the metal. You might even place the plywood over a shallow dent in the ground. Nothing is truly finished unless it has been beaten on with a hammer!

Another thing to try would be to anneal the metal by heating it up to a dull red and then letting it cool naturally (normalize), and then working. That allows the molecules to relax and spread out a little, and removes most of the memory effect also.

You're joking of course, right?
Wailing on a 1/8 thick sheet of aluminum with a 2/4 and sledgehammer?
Heating aluminum to dull red?
Sounds like a prank to pull on a shop apprentice.
When he's done, send him out to pick up some chrome muffler bearings.
Next time order thicker stock to allow for milling or get precision ground steel plate.

Sorry Cota, but if you got out of your cubicle and into a metal shop you might realize there are many ways to skin this cat. Thanks for a smart ass rebuttal when I was only trying to help a guy out.

Yes, I would work 1/8" with a sledge.The sledge weight and hammer force can be varied. Do you think this is a large thickness or something? With aluminum you could probably could do this up to 1/2" thick.

Yes, aluminum melts at 1220 deg f. So a forge or a kiln would easily get the metal to around 800 deg. and then allow to cool. http://www.metalshapers.org/tips/covell/annealing.shtml

Still need to find out how box is to be joined together. Does it need to be airtight? What will it contain?

Peace

bamwa - the box won't contain anything (nor is it structural). it will be joined with metal epoxy.

Thanks for the ideas. I need to try the sledge idea. I tried with a deadblow hammer to no avail, but I'm sure a sledge would have a lot more force.

Sorry Cota, but if you got out of your cubicle and into a metal shop you might realize there are many ways to skin this cat. Thanks for a smart ass rebuttal when I was only trying to help a guy out.

Yes, I would work 1/8" with a sledge.The sledge weight and hammer force can be varied. Do you think this is a large thickness or something? With aluminum you could probably could do this up to 1/2" thick.

Yes, aluminum melts at 1220 deg f. So a forge or a kiln would easily get the metal to around 800 deg. and then allow to cool. http://www.metalshapers.org/tips/covell/annealing.shtml

Still need to find out how box is to be joined together. Does it need to be airtight? What will it contain?

Peace

I've been a machinist for 30 years not a desk jockey.
A sledge on a piece of material that could be bent with your bare hands is a bit of overkill when he only needs a deflection of .004.
I don't care how hot you get aluminum, it's not going to get dull red.
Passing a sooting flame from a torch over it is all that would be needed to soften it
Ever watch american hotrod or american chopper making a gas tank?
Peace Out

Although I don't see any need for the arguing - I will chime in to say that there's no way in hell you can bend 1/8" x 3" 6061 by hand.

OK, maybe I should have said I could bend it bare handed.
I forget that I'm among mere mortals.:D:D:D
Just thought it was some troll having fun with you being it was his 1st post.

Cota - I will pay for the gasoline if you can drive over to my place and bend this stuff into tolerance by hand ;)

I would but my cape and tights are at the cleaners:D