The first time I saw a shrinking disk in action I could only think, "THAT'll never work!"
And then it miraculously did it's thing, much to my amazement, and the metal shrunk.
There are a lot of metal working tools and techniques that I am totally unaware of, so I just plod along doing the best I can with what I have. I do have a 150# antique blacksmith's anvil, though.... One of a few things I inherited from my Dad's shop and it comes in very handy now and then. It's just a total bear to move around in the shop and it takes three strong people to get it up on top of a stand so most of the time it just sits in one spot.