Milling Machine Tool Holders - 2: CNC 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 manual machines and CNC machines use tool holders that have been precisely ground with a male taper that mates with the machine's specific female taper. There is also a way to secure the tool holder in place with a retention knob or a draw bar thread. With CNC machines, the retention knob is more popular because it allows for easier automatic tool changing.

There are two typical taper-flange types on CNC machines, the V-flanges and BT-flanges, but they are not interchangeable: The V-flanges are also called CAT or Caterpillar because the standard was developed by Caterpillar Company (top right). The BT-flanges are more popular in Europe and therefore found on European machines (right).

There are different sizes within the holder types. The typical sizes are 30, 40, 50, and 60. Although the taper is the same for each type (the same angle), diameters increase with the size numbers shown in the animation below. Larger sizes are for larger machines with more horsepower.

It is unusual to find built-in tools in these tool holders like the R8 tool holders. In nearly every case they heave a precision ground I.D. in which to mount end mills and other tools. Collets, when used on CNC machines are of the ER type (right)

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