I own one of these machines. It is a waste of time to loosen the tensioners unless the belt is too loose overall. Just spin off to the smaller pulley in whichever direction you are going. Keep the bed away from the end of the ways(z Axis for lathe, X Axis for mill), or it will lose considerable accuracy. I have in practice turned a shaft down to 5 ten thousandths over 6 inches, but it's not a machine that's meant to last, so over time it will need adjustment and replacement parts, and generally new parts made from scratch. There are not really Gibbs on the screws, so for practical use, these must be added. This is a tool that works well for learning machining, but not a machinist's tool. Once you have readily used real machinery, you will learn that it's only suited to roughing, and anchoring marine vessels.