Here is a pricking iron I made from a 1 inch spade bit. These bits are quite hard and would need to be annealed.

To anneal the bit, I would heat it up to a bright red, nearing on orange, and then left it in a bucket of ashes to allow it to cool very slowly. This makes the steel very soft and easy to cut with a file or a hack saw.

After the steel is annealed the tip was lopped off and I marked spaces for the teeth with a triangular file while using a rule to get the right spacing.

I used a hack saw to cut the right length down. After that the spaces were widened appropriately with an angle grinder to make room for a file. I filed away material evenly so the spacing wasn't ruined.

The pricking iron was then heated to a red and then quenched in oil to harden it and put into a toaster oven to bring the temper to a bronze colour.