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What is a Jacobs Taper?

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  • Written By: Paul Scott
  • Edited By: R. Halprin
  • Last Modified Date: 23 September 2016
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The term Jacobs Taper refers to one of a family of tapered machine tool shafts used to lock the tools in place in drill presses, lathes, and milling machines. This group or family is collectively known as machine tapers and offer a cheap, efficient alternative to conventional jawed chucks. The machine taper has been in use since the earliest manual drill, milling machines, and lathes and is still used as a reliable tool mounting system on modern computer numerically controlled (CNC) machines. Unlike convention chucks which rely on the pressure exerted by three or more jaws to secure a bit or tool, the machine taper relies simply on the friction across its surface and the pressure against the work piece to hold it firmly in place.

The different members of the machine taper family all work on the same basic principle. The tool shaft is tapered and is simply inserted into a similarly profiled socket in the machines head or chuck. Friction across the two mated surfaces and the pressure exerted by the work piece hold the tool firmly in place. This simple system produces considerable torque transmission and a very secure grip on the tool. These tool shafts and their corresponding chucks typically have a slot cut through them allowing a wedge to be used to dislodge the tool when the job is complete.

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Other variants in the machine taper family include the Morse Taper and the Brown and Sharpe Taper. These machine taper groups all feature a set of different sizes graded according to their taper profiles which are defined by three basic dimensions. The first is the diameter of the taper at its broad end or major diameter, the second is the diameter at the narrow end or minor diameter and the third the axial length between the two. The Jacobs Taper is generally represented by ten different sizes all of which are typically used in light load applications such as drill presses.

Jacobs Taper chucks are far cheaper to produce than conventional jaw types and tools may be changed a lot quicker using this system. The Jacobs Taper and its counterparts in the family have been in use for many years and are still popular tool-locking options even on modern CNC machines. The Jacobs Taper chuck and tool shaft system is most commonly found on larger, commercial drill presses although smaller do-it-yourself (DIY and hobby machines are available with the locking system.

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