Marples Gear cutting is any machining process for creating a gear, such as hobbing, broaching, milling, or grinding. Such cutting operations may occur either after or instead of forming processes such as forging, extruding, investment casting, or sand casting. CNC Machining is a process used in the manufacturing sector that involves the use of computers to control machine tools. Tools that can be controlled in this manner include lathes, mills, routers and grinders.