Inner-cooling indexable step drill and method for fabricating step hole

The invention provides an inner-cooling indexable step drill and a method for fabricating a step hole thereof. The inner-cooling indexable step drill comprises a fixed part and a drill bit body. The drill bit body is in columnar shape with steps. The outline of the axial section of the drill bit body is in step shape, and the outer diameter of one end of the drill bit body near the fixed part is larger than the outer diameter of the end far from the fixed part. The top of the drill bit body is respectively provided with an end inner knife block used for processing the central part of a hole and an end outer knife block used for processing the outer part of the hole. A step-shaped jut of the drill bit body is provided with an indexable blade. The surface of the drill bit body is provided with two spiral slots for containing drilling chips and cutting liquid. A material part of the drill bit body is provided with two spiral holes used for filling the cutting liquid with certain pressure. The invention also prov