Correcting a warped tray?

[Smokin' Coke Forge]

So, today I was working on finishing up a candle tray for holding 4, 3" pillar candles.  The tray is 4 1/2" wide x 21" long, with a 1 1/2" rim welded around the circumference at a 45 degree angle to the base.  The material is 3/32" thick.  The legs are 3/16 thick by 3" wide, and will be riveted to the base of the tray   where the scrolls meet.
 
Before riveting the legs to the tray, I heated the tray, using a rosebud tip, to a black/dull red heat.  Once heated, I applied a wax finish.  Next I waxed the legs.  The next step would have been to rivet the legs to the tray, however, I noticed that after waxing, the tray had warped about 1/2" from left to right along its length. (It was perfectly flat before heating for the wax finish)

 

In this pic the tray is set on the legs but not riveted on.

 

 

Here, the tray is upside down with a rod agross the length to illustrate the warp.

 

Does anyone know of any way that I can correct the warp?  I saw a post that suggested heating the convex portion of the curve, then applying a wet rag to cool just the top side of the plate, but I'm not sure if this would work considering the rim that's welded around the outside.  I'm hoping that this can be salvaged, since it is supposed to be a Christmas gift, and I won't have enough time to make another.

 

Thanks in advance for any suggestions.   - Jim

[Charles R. Stevens]

The simplest way is to reheat the pan and flaten it, in cold work you would identify where it needs srunk or streched to make it flat. Might take a couple of cycles

[jeremy k]

Have the long part bent (sides and bottom) to the shape you need and weld in the ends as needed. Weld shrinkage on that long of item is tough to control.

Also in your heating you may have heated the bottom more than the edges and that caused the warping, heating the bottom and not the edges will in effect "upset the bottom" as the edges will hold the shape till it cools and the bottom will shrink and cause the warping. Been there done that - even heating is key to keep from warping.

[Smokin' Coke Forge]

Would it make sense then, to gently heat the plate from the high, top side, across the narrow width near the center of the tray, then cool just the top side?  I'm thinking that if I do a little at a time - heating across the width of the high side, cooling, then repeating while gradually moving away from the middle, it might pull the far ends back up?  Based on what's been described as the possible cause, and what I've read in another thread from back in May that contained some good information about "line heating" to straighten thick plate, it seems that I may be able to reverse the warp usng the same priinciple if I go slowly without applying too much heat.

 

Barring any other ideas or suggestions to the contrary, I'll give that a shot tomorrow and reply back with the result.  Thanks for the input!  Much appeciated.   -Jim

[Charles R. Stevens]

Hard for me to really tell from the picture (I phone, lol) but is the pan twisted or just tweaked curved along its length? If its along its length try stretching the sides. To be honest a round in a self cleaning oven might reduce the stresses enough,

[BIGGUNDOCTOR]

The metal has shrunk on the bottom side causing the bow. I have straightened bent conveyor sides with heat. Apply the torch on the bottom side until it is a dull red, and slap a wet rag on the top side that needs to be shrunk. Worked like a charm on the conveyor.

Hammering will stretch the metal making things worse.

Another option may be to heat the entire piece evenly, and see if it will normalize.

[swedefiddle]

The wonderful wiggly world of hard clay (steel).

 

I guess this is your lesson of heating and shrinking. You warmed it up to too high of temperature, unevenly.

Heat it up to red, clamp the base with a piece of thick flatbar the size of the bottom, when hot tap the sides with a flat dolly and a soft hammer.

Steel dolly and steel hammer = stretching the material.

Steel dolly and soft hammer (wood, leather, lead...) = shrinking  shrinking the wrinkles (just like the ladies do!!!!)

 

Artist privilege means, "That is exactly how I intended to make it" "It is not crooked, It was planned" :) :)

 

Merry Almost,

Neil

[Smokin' Coke Forge]

Thanks all for the replies.

 

Charles - The tray is only warped along the length.  It's still flat across the width, probably because there isn't enough metal in that direction to noticeably stretch.  Thankfully, it did't twist along the diagonal length either.

 

Biggundoctor - I'll probably try your suggestion first, since it seems to be the least aggressive solution.  Are you suggesting that I evenly heat the entire bottom, or just a smaller section in the center?

 

Neil - Great explanation about stretching the bottom side with a steel hammer vs shrinking the top side using a soft hammer.  It sounds very similar to the stretching behavior that occurs on the outside of a bend vs the upsetting on the inside of the bend, but with much more finesse. It's the lack of finesse that got me into this mess in the first place, so a great suggestion that I use it when trying to get out of it.

 

Thanks again.  If I can get these techniques to work for me, I have a bunch of ideas for how I might be able to use the lesson to add some intersting "features" to some future designs.  -Jim

[BIGGUNDOCTOR]

Start small, as you don't want to warp it the other way. Work in the center of the warping, and work your way up bigger till you see some movement. I used a bucket of water, and rags on the conveyor. For that one it was a straight bend in the upper section. I ran the torch up and down till it was red hot, then applied the wet rag to the side. It would move one inch each time I cooled it.