Not a blacksmith but I do play with it and make knives for fun. I wanted a diagonal peen hammer for a while now and decided to make one from a 4# engineers hammer that I was given. I used an angle grinder with a cutoff wheel to rough out the head following the indents on the side of the head. Then I ground the sides that I had cut off to form the diagonal. After that I did the same thing on the other side to form the reverse diagonal. Now the hammer has a left and a right diagonal peen. I used the angle grinder because I have one and because it worked. I was able to keep the temperature of the head cool enough to touch by quenching it when it got warm. I believe that kept the original hardness in the hammer faces (at least it seems that way). Total time from start to finish was about four hours give or take.
