Milling Machine Tool Holders - 3: Special Tool Holders
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
Large machining centers often have a coolant station that is very complex. That coolant station is providing coolant through the tools to increase the amount of fluid that gets to the cutting action. Coolant stations are usually made up of a series of filters that remove impurities and chips that have been carried in the coolant and pumps. Some coolant stations provide pressures in excess of 1000 pounds per square inch to the cutting action. As a comparison, the amount of pressure that comes out of your garden hose at home is about 100 pounds per square inch. This ten-fold increase in pressure allows for a very good removal of chips, significant cooling, and a much better surface finish on the work piece.

With the increased use of high speed machining at RPMs of up to 10000, conventional tool holders demonstrate their limitations. To avoid slippage of the end mill in the tool holder and to ensure a balanced load for the spindle, shrink-fit tool holders, as shown on the right, were developed. In this case, a tool holder is actually heated so that the bore will expand in size and allow the oversized end mill to fit inside. When the tool holder cools (shrinks) down, it securely holds the end mill since its bore size was smaller than the end mill to start with. Prior to being used in a machine operation at high RPM, the tool holder is balanced just like a car wheel is balanced using a mechanism on the tool holder. Note that there are other methods of balancing the tool holder such as drilling small holes in the tool holder at selected location.

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label: milling machine, tool holder, collet, r8, international, CNC machine, high pressure coolant, shrink fit tool holder