well...the manufacturer has some recommendations. On my vikings....regular cleaning of the bobbin area is needed....but there is no requirement for my oiling anything....but...the viking tech said that there are places internally that do need oiling periodically and if I take the cover off, I void the warranty. So the recommendation is once per year. And embroidery units also have places that need oil periodically which is done by a dealer. My APQS long arm has a few places I oil and the manual and website have information on more maintenance I can do by myself including repacking with grease....so generally, I try and run each of my machines at least every 6 months and to take them in every year or two for servicing. The newest and most expensive...I really try and get them in once a year....the older ones....well, it is getting to the place where the cleaning and servicing might cost more than the machine is worth.