A machine taper is a fastening system which uses the principles of friction to securely lock a tool bit into the spindle of a machine tool. This is achieved by machining a tapered profile into the shank or shaft of the tool bit which fits into a mirror image recess in the machine tool spindle. Pressure against the work piece firmly seats the machine taper and friction across the whole area of contact holds the bit securely. Tool bits designed for light duty applications usually rely on this friction alone to secure them while those used in high torque machining may also feature a key system or be threaded. There are several types of machine taper in general use all of which share the same basic principles and offer a quick, simple, and cost-effective method of tool bit locking.
Tool bits designed for use in drill presses, milling machines, and lathes require a secure locking system when in use. Operational bits are subject to considerable amounts of force, and a badly secured tool bit can ruin a work piece, damage the machine, or cause serious injuries to the machine operator. Machine tapers achieve this locking action by mating a taper machined shank to a corresponding recess in the spindle. The friction created across these two surfaces creates a surprisingly secure connection and is capable of transmitting considerable torque to the tool bit. The simplicity of the design also means that bit changes are quick resulting in improved productivity.
Machine taper designs meant for light machine use such as drill presses typically rely on the friction created by the taper alone to lock the bit. Heavy duty machine tapers may also include a thread cut into the two surfaces or a draw bar system to improve the seating of the taper. Some heavy machine taper designs incorporate a key feature which also helps in resisting the high torque forces involved. Many tapered tool bits feature corresponding slots in the bit shank and spindle which allow a wedge to be used to firmly seat and dislodge the bit.
There are several different designs of machine taper used to secure tool bits including the Morse, Brown & Sharp, Jarno, R8, and Jacobs Taper variants. Each member of this family features slight variations in design although they all function in the same way. Each machine taper series typically feature a range of different sizes and are generally sold in sets. This tool locking system is far easier cheaper to produce than other types such as jawed chucks, thereby making the machine taper a particularly efficient and cost effective device.