How to flatten this piece of mild steel?

[Phil Thien]

I have this piece of mild steel I use as a template for cutting pieces of paper (an odd shape) for a special purpose. It is approx. 7" long, 1" wide, and 1/8" thick.

Over time it has gotten a bit bent out of shape (sort of like a sine wave). I've tried placing it between pieces of mdf and leaving it in a vise for a couple of days but it just springs back to its shape.

Anyone have any tips for getting it flat without changing its overall shape?

Edit: I was going to place this in OT but I guess I stuck it in the wrong forum. Moderators please feel free to move it. My apologies.

[Leo Graywacz]

You are going to have to bend it beyond its straight point in the opposite direction. The way I would do it is place it with the curve facing up so the high point is up. Then on the areas that are touching the table raise them up the amount that the gap is under the bend. Then whack it with a hammer a few time...gently. Keep looking at it after every wrap and when it gets straight you're done.

[Lloyd Kerry]

If you need it very straight, you could take it to a local metal shop, they'd probably do it for nothing, or next to nothing.

[Aaron Berk]

why would u fool with it?
And if you took it to a metal shop they would laugh you out of there.

Just get another one

[Carl Beckett]

try something like this:

turn it so it bows up. Then put a shim on the points that contact where it is sitting. Press the high spot down (use a clamp to squeeze it down). Release it and inspect. Adjust the shims to get more bending, or adjust the position.

As Leo says - you need to bend it beyond straight in the opposite direction (just clamping between blocks only brings it to the straight position each time, then it springs back - so you have to go past straight). The trick is knowing how much. So you have to bend a little at a time.

A little patience and you can usually improve it at least.

[Phil Thien]

why would u fool with it?
And if you took it to a metal shop they would laugh you out of there.

Just get another one

What you can't tell from the vantage point is the special shape of the piece. It took a couple of hours of trial/error to file it to shape.

[Charles Lent]

Mild steel isn't very expensive, and the dimensions that you give don't appear to be critical. I would think that it would be very easy to just have some 1" X 1/8" stock cut to the 7" length. Could it be this easy, or do these dimensions have tight tolerances?

Charley

[Charles Lent]

Phil,

We were posting at the same time. Can you provide more detail (dimensions and accuracy) for what you need? I may be able to help.

Charley

[John Coloccia]

How precise does it need to be? The concern straightening something like this is always stretching or shrinking the metal. It's probably stretched already at the bend, and straightening it could well make it wavy at the edges. That said, if I really wanted it straight, I would probably just clamp it in a vice, give a little tug, move the vice up a bit, tug a bit more, etc etc. By carefully setting the vice and where you're tugging, you should be able to flatten that to dead straight.

[Jay Jeffery]

I have this piece of mild steel I use as a template for cutting pieces of paper (an odd shape) for a special purpose. It is approx. 7" long, 1" wide, and 1/8" thick.

Over time it has gotten a bit bent out of shape (sort of like a sine wave). I've tried placing it between pieces of mdf and leaving it in a vise for a couple of days but it just springs back to its shape.

Anyone have any tips for getting it flat without changing its overall shape?

First the bad news:

Strictly speaking, what you want to do is impossible. Once steel is bent, it has also stretched. It's kind of like really stiff taffy. The other issue is that the part that has stretched has become harder than the rest of the material (ie "work hardened" or "cold worked"), and will be less inclined to deform that the part that hasn't stretched. So any attempt to make the bent part not bent is more likely going to bend the area around it.

Another aspect of metals is that their properties are not time dependent like wood or plastics. So leaving a piece of steel in a shape overnight, 15 minutes, or 100 years won't matter.

Some tricks to try:
Locate the point that is bent and mark it if you want to. Place the straight part between 2 blocks of wood or other material to hold it securely. It works best if one of those blocks is a table. You want to make certain that the flat metal near the bend cannot deform. Gently bend back the material just next to the blocks, but not the entire piece yet. Move the blocks in over the section you just straitened and repeat until the bend is gone. Move on to the next bend. Wash rinse and repeat until flat.

If that doesn't work, the only way to straiten the piece will be to remove a thin kerf of material where the bend has occurred, straiten, then weld in the kerf. You can then grind and sand the weld flat. If you are lucky the weld hasn't warped the material too badly and it is straight enough. If the piece is angle iron, tubing, or anything like that, this is the only way to straiten it.

In some applications, you can beat it flat enough on an anvil, but if you had to file this thing to shape, that just isn't going to work. There are also cases where heating the metal with an oxy acetylene torch can help. The torch not only makes the material easier to bend, but it undoes the work hardening caused by the bend. I mention these just for those who run across t his thread int he future, not for the OP.

Best of luck to you.

[Van Huskey]

What you don't have a metal jointer???

[ian maybury]

It might be as easy to make another Phil, but it's so far as i can remember possible to get very close to flat using the sort of forming rolls that metal fabricators have.

There's various techniques, but the sheet metal guys often flatten their material by passing it through a set of forming rolls so that it's bent into a curve. Then flip it over, reduce the offset of the middle roll and and progressively ease the curve out in successive passes until it's straight.

There's more sophisticated set ups too http://www.youtube.com/watch?v=htpLxvKkWgA (maybe somebody within range of you has the equipment), but most sheet metal guys should be able to get close with a set of forming rolls.

The principle is that by overbending it in one direction, and then the other opposing stresses are set up in the top and bottom surfaces that hold it straight. It may not come quite perfect all over (there's some residual stress left in the centre of the sheet), but provided it's mild steel that'll take a decent bend in both directions without problems it shouldn't be far off.

There's techniques used in production to flatten coil material that involves compressing the steel between 'nip' rolls, but that would enlarge your piece.

ian

[Phil Thien]

Thanks for the tips everyone. I took the advice and clamped it in a vise at various points along the length and tugged (slightly) the bends out of it. I took my time and made certain as I nudged it a tiny bit that it was going to bend where I wanted.

It only took 10 minutes and it is pretty darn flat and very usable now.

[michael a nelson]

could you post a side pic i am very curious to see what this thing looks like