Inside: How to use a round punch is an important concept to master. How to forge the hammer or struck end to the round punch, and how to forge the tool end of the round punch.
When looking at tools you will need as a blacksmith, the round punch may top your list for two reasons. One, it is easy to forge a round punch; and second, the round punch is extremely useful. I usually make most of my tooling using repurposed coil springs. If you have access, buying some 5/8ths or 3/4 round stock in 4140 carbon steel, will make a good set of predictable tooling.
Using a Round Punch
When I first started forging, I could not believe how simple the round punch is to use in concept. The idea that you can just heat up a piece of metal and punch a hole straight through, intrigued me. Although, I must admit, actually punching a clean hole in the metal, took me a little practice. Some of the challenges that I faced were, getting the hole centered in my material, and punching the hole clean without any rag. Rag is the jagged edge of material left behind inside the hole after being punched. This could be from not tearing through at the right temperature, or it tears in the center first instead of along the edge of the hole.
With practice though, you should be able to line up your punch to the location that you want to punch your hole, punch through the majority of the material while it is hot, then at a lower temperature tear back through from the opposite side. This should leave a small slug that will pop out of the hole. The slug is a small volume of material that is left from the hole punching process.
Forge the Hammer End of a Round Punch
The hammer end of a round punch is the end of the tool that will get struck by a hammer. Now how ever you decide to do this, you will probably perfect your technique as you use it on the hammer end of all your hand tools. When I first began researching tools and how to forge them, I came across this reference on pg 61 of the Skills f a Blacksmith by Mark Aspery. It is a good write up on forging the hammer end of a hand tool using what I call the octagon method. I have since come to use what I call the hexagon method, as I found it more pleasing, although a bit trickier at first.
So to form the Hexagon on the hammer end, first begin by forging two opposing flats. These will want to be extended an inch to two inches from the end. I then rotate 60 degrees and forge two more opposing flats. Rotate 60 degrees again and forge the last set of opposing flats. You should be able to see the hexagon shape on the end at this time. Take time to clean it up and make each face equal and even. I hot file the end making sure to remove any hollow in the center and round the corners down a bit.
Forge the Tool End of a Round Punch
Most of my hand tools begin this same way. First forge a square taper, approximately 3 inches long. The goal is to get the small square on the end to match the diameter of the size round punch that I want to make. After completing the taper, forge the square taper into an octagon taper. Once the octagon taper is completed, I find it a smoother transition if I forge out the 16 sided taper. Finish up the forging by planishing it round, by rotating continually and never hitting the same spot twice.
Grinding the Tool End of a Round Punch
I use two different types of shapes on the ends. The flat grind, which seems to give me better looking success on thinner material. Along with the 120 degree bevel, which works more efficiently on thicker material.
I hope that you found this to be helpful as you are building out your own tooling for your forge.