After having a go at metal shrinking with a gas torch that has now run out of gas, After seeing a video on you tube how to shrink metal with a disc I thought I'd try and make one and see how well it worked.
I started with a piece of scrap stainless 0.050" thick, cut from a removed commercial kitchen bench. drilled a great big hole 7/8" in it to fit a angle grinder. When I stuck it on the grinder it nearly severed my hand off. It was to big, wobbled like buggery and was sharp enough to sever a man's head
To stop loosing an appendage from the disk vibrating and the samurai sword edge. I trimmed the edge to 7 " diameter and to a perfect circle to balance the disc and dull the edge.
To get the curve across the surface of the disc I attached a bolt through the center hole and held it in a vice so it was able to just spin. I placed a dolly under the disc and rested it against the vice. As I hammered I made each blow move the disc. After each rotation I moved the bolt position in the vice to set the dolly closer to the edge, I used a pointer dolly to get a steeper curve at the edge.
After each turn the disc started to look and sound more like a cymbal. I kept hitting it till the curved looked steep enough to touch the metal with out cutting it with the edge and stop the center thread of the grinder scratching across the panel surface.
The best way to describe how it works is to watch the youtube video, I found it a bit noisier than I expected, Its also hard to get a wet rag to cool hot metal in one hand while you are trying to man handle a lethal cutting disc in the other. I think it will take a bit of practice getting the timing and movement right to get the desired shrinkage.
After a few quick goes I had to adjust the center nut to replace it with a flush one. I needed to squeeze the nut into the disc to make it fit, this made the hole a little bigger and harder to get the disc dead center. This now let me get the disc flatter on the panel making it just hit the panel high spots.
