Before you ask: Yes, Chisel is my real name. No, Chisel is not my birth name.
I was born in 1974, and soon christened something that definitely wasn’t Chisel. I grew up, finished school, finished my A-levels and went to university. Being such a kind soul I joined Rag. This was (and probably still is) a group of people who went out with collecting tins to collect money for various charities. One of the informal rules was that the members of Rag had to have a nickname. After one collection in Sheffield, the group was counting up the money collected for the day, someone looked at me and realised that I didn’t have a nickname yet. I was standing there with a collecting-tin in one hand, and a chisel in the other. [one effective method for opening the collecting-tins]. So I became Chisel. In many ways this was quite lucky; I could have been called Collecting-Tin. I got off better than other group members. Ask Shaggy and Dribble if you don’t believe me.
For some reason, my flatmates found out about the nickname, and started using it. The nickname just spread, like some social variant of Code Red. Soon everyone was calling me Chisel. Soon after I was introducing myself as Chisel. After a few years of this, I got fed-up with bills and statements arriving addressed to someone I no longer associated myself with. So I found a suitable website, and changed my name by deed poll.
And thus, Chisel was official.