Green’s Dictionary of Slang

1. (US Und.) to break into a safe.

1930

J. Black ‘A Burglar Looks at Laws and Codes’ in Harper’s Mag. CLX 307: While he was inside doing the ‘blacksmithing’ on the bank vault, his outside man, his lookout [...] went to sleep in a hallway.

2. (US gay, west.) to work as as a pimp.

2022

(con. late 19C) J. Nevins ‘Western frontier gay slang’ on Twitter 2 Mar. 🌐 ‘blacksmithing’ = pimping for a prostitute (male or female).