This is my newest notcher made from a piece of 1/2" copper tube, smashed flat on the end.
You can see the big U flakes it was taking. I hurried through these notches just seeing how the 1/2" copper would work and I broke one of the ears off when I let it slip forward as I swung at it. You can see some of the U flakes it was taking out. I've been using 3/4" copper the same way but it doesn't seem to work quite as well as this did.
I was hitting it with a 1-1/2" round Osage rod about 12" long at a slight angle so the billet contacted the copper on the back side and it would drivr the flakes ahead real nicely. The 3/4" always seemed to drive the flakes too far forward, more long and skinny and would cause the sides of the notch to be really steep. I never got good U flakes with the 3/4" copper.
Anyways,, this was just a quick test with good results so I wanted to share it. The preform was already broken and glued back together as a practice piece.
I could have taken more time with the notching but I done wore myself out working on my front truck axle. It was a mess, and I was tired.