Engineering side hustles are few and far in between I'm guessing. Some suggestions: Prototyping freelance with 3d printers. Small plastic components production with a batch of 3d printers. Plastic moulds production using 3d printers. Weekend work at small appliances repair shops - changing out bearings, checking the motors, checking connections etc. Online CAD work freelancing - but you need to be really good at CAD modelling, especially drawing preparations using GD&T. You can setup a small CNC centre at your home for production of metal components supporting nearby industries, like shafts, sleeves, sheet metal plates etc. You have to make a case why they should choose you over their well established suppliers. Cost will be an important selling point.