Correcting slight bow in piece of 1/8" x 3" stock

[tikka308]

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!

[fretsman]

Do you have any room to machine the thickness?

[tikka308]

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!!

[fretsman]

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

[tikka308]

No need to apologize!

[MetalBlade]

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.

[fretsman]

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 -

[cjdavis618]

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.

[cam1]

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

regards

[Robin Hewitt]

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.

[fretsman]

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?

[Robin Hewitt]

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

Makes a mess of the surface in all.