Flattening a piece of 1/8 sheet after texturing it.

[dbtabasco]

So I am working on a table top. It is a corner table and the top of it has got a hammered texture (small pien used an air hammer to do it)

My problem now is getting it flat.

The piece is 1/4 of a ring (id 40" od 80") and for the life of me every time i hit it in on place to flatten it another area rises. I generally don't do a lot of sheet metal work like this so am having a xxxx of a time figureing out where to hit it to make it flat. I don't have a forge large enough to get a good heat on any significant amount of it otherwise I would heat and strap. Oh and the sheet is 1/8 (or 11 gauge)

https://picasaweb.go...feat=directlink

Any thoughts or links would be helpful.

[pkrankow]

Is it getting fastened into a frame at some point? That will hold it flat if it is pretty close.

You don't have to heat the whole piece at one time, but can heat the areas under the highest tension/compression and it should flatten. I use a piece of #11 steel as a fireback in my fireplace, and it always curves, so much in fact that I turn it around to warp back the other way. Uneven heating will make thin metal like this move all over the place. It takes some skill to do this right (and I lack the skill to tell you how because all I know is guesswork)

I believe this can be done with a rosebud torch, as you do not need to get the metal to red heat, just a high black heat will do.

I have boxes of Christmas decorations in the way of the fireplace so I can't just check which way the sheet warped right now, but IIRC the well heated center tends to move away from the heat and the less heated edges move (or are forced) towards the heat.

Phil

[Ric Furrer]

tough job....you have work hardened it in a non-regular pattern on a non-regular shape.
If you can not evenly soften the sheet then counter bending may be a viable way to go.
Induce a bend in one direction and then slowly work it out. Nothing says you can not drive a car onto it with some wood blocks under to induce and then remove the bend.
You may be able to get it close by placing it on the table base, weigh it down with a great weight..tons ..and then tack weld in place. If the base is strong enough it will hold.

The simplest would be to heat the while sheet and lay it flat under a large flat platen to cool.

If you can not get it to work to your liking then I suggest:
1)texturing an oversized plate..10" larger in two directions
2)take it to a three point bending outfit (they roll tanks and such) and have them counter-roll till flat
3)cut out your table top


I have heard for some folk who could flatten large plate with a torch and water..selectively heating in areas and cooling them to pull it back into shape, but I have had no success with the technique.

Ric

[781]

Ralph Sproul teaches to use a weighted rawhde mallet. The kind that has a wood handle a metal head that takes replaceable raw hide faces. use one side for hot work and the other keep clean for cold work

[peacock]

It's possible that when you textured the sheet you thinned the middle more than the edge. I would try taking the air
hammer to the perimeter maybe an inch or so as you pein it it will grow alowing the center to lay down. This is kind of like what they do when they hammer a saw blade.

[macbruce]

The mallet approach sounds good.....One thing I think would help is say a piece of 3/4 plywood with a 6''-8'' round hole in it to pound down high spots into it...good luck

[bigfootnampa]

So now you need to shrink each high spot/area until it lays flat and then flip it and do the same on the other side (essentially shrinking each LOW spot/area). This is standard auto body type work though your metal is a bit thicker than normal. There are lots of YouTube videos that will help you to get the basic idea. Not as hard as it looks but requiring lots of patience and time consuming care. Some sort of soft mallet is needed (wood, plastic, rawhide... rubber can work but is too soft to be efficient). Localized heat can be helpful but may not be necessary. After flattening you'll probably need to tune (grind) your outside edges a bit to get your shape faired in.

[jeremy k]

Peacock is correct - I have had this happen with 1/4" plate during texturing and had the 1/4" plate do wierd things other than stay flat, working the edges was the answer. when textureing plates of larger shapes, keeping the texturing even throughout the whole piece is the key to keeping it flat. Shrinking the high spots is - yes one answer, although in sheet metal that is easily done - heavier plates - it is easier to (fuller/expand) the areas that are holding the tension. Plywood is a good backer for the 1/8" sheet, I use a 1/2" rubber floor mat for cold straightening 1/4" plate.( a 24" square plate for a table top is what i've had to work with and straighten)

[macbruce]

<p> Largish copper, brass, bronze and aluminum sheets can easily be annealed with a weed burner so no problem compared to steel. I found that texturing both sides of steel plates/sheets as well as the others mentioned helps to keep warpage in check which is how I did the background in the ''Holly'' piece. It's nearly impossible to do by hand with an opposing die similar in shape below the sheet and hammer. For larger plate I have opposing mill ball dies and texturing dies for both my PH's
The process is then drawing not plainishing which still presents problems in confined areas. If the plate is free to stretch it stays pretty flat.

[dbtabasco]

Thank you for all the replies, I found a guy with an oven and a willingness to heat and weigh the piece down. Will let you know how it turns out.

[SmoothBore]

When I was a boy, ( half a century ago ) there was a little junkyard down the road, where the owner did body work on cars and trucks.

I've often seen him shrink a dent out of a body panel, by heating a circle around the dent with a rosebud, and then quickly cooling it, with an air hose.

Obviously, it takes some practice to get a feel for this process, ... but it is possible, and it's better then hammering more stress into the piece.


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