Very simple trick for all you amateur locksmiths. It’s a highly simplified field-expedient variant on the Falle improvised-key system.*
* (The one where you cut a key out of pre-etched steel blanks with a pair of scissors. Neat because you can repeatably cut to code by eye.)
You use a photocopy of a key as a template to cut the key out of a plastic card. The natural play of the card in the lock and inherent tolerances of the mechanism provide enough leeway to make it work.
“if it’s a standard vertical key without sidebars and extra security pins, I generally put it on a photocopier, and then cut that shape out of a plastic card, works fine (use a tension wrench to turn the lock, not the card, as it will break).”