Trepanning is a special process used to produce holes or circular grooves by using one or more cutters and revolving them around a center or core. Typically this operation is used when conventional machines are tooled up to do deep hole drilling. Usually in such cases the machine power is less, so solid BTA drilling is not possible. Trepanning is also used when a solid core is required. The trepanning operation is performed on a blank workpiece without any holes. The tool geometry allows cutting only on the circular section whereas a solid core is left in the middle. This core can later be extracted for use. Typically only through hole applications are advisable with trepanning since the core extraction can become troublesome, as is in the case of a blind hole. The tool covers a large range of diameters up to 500mm. There are limitations to achieving smaller diameters of this process due to the geometry of the tool. Trepanning is commonly used for such things as weight reduction in finished parts, clearance, fluid flow, work cavities, machining blanks, piston and cylinder features, and seals.