DH changes the oil in our vehicles evbery 3,000 miles, so I go with that thinking for my machines. Since the motors and mechanics of the machines are much smaller, I oil and lube my Featherweights after about 8 hours of sewing or if I get caught up and can't that often, at least once a week if I am using them for a particular project, I too, oil, let sit and test on a piece of fab. I oil my Bernina after every big project, and often during the process of the project if it is a quilt or big project.