I've seen recommendations to change your needle as regularly as
every 4 hours of sewing, however if I am stitching light gauzy cotton fabric I won't change my needle as often as if I am stitching a heavy denim which will blunt my needle faster then guaze will. I might use an already used needle on the denim but a brand new super sharp one for the gauze. Does that make sense?
You should change your sewing machine needle:
- when it has been damaged by hitting a pin, zipper or anything hard (even if you can't see any damage)
- regularly - when you think it's not sharp any more or when you start a new project
- it's all gummed up with sticky stuff from iron on interfacing and you can't get it clean with an alcohol based cleaner
- you can't remember the last time you changed your needle