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Technical Section Phone: 516-328-3970 www.technocnc.com  11 Collets   There are two basic types of collets, half-grip and full- grip (see top right). Half-grip collets are identified by slits running from the bottom (or “mouth”) of the collet toward the top for about 80% of the collet length. This type of collet grips the router bit at the mouth of the collet. Half-grip collet is the simpler of the two collet types, and is ideally used with shorter shank tools where the shank would not fill the entire length of the collet. Full-grip collets have slits running up from the bottom and down from the top, again for about 80% Pull Stud Note: This is a maintenance item and  should  be  replaced  every  6 months. HSK Tool Holder Note: Always make sure the tool holder and  collet  nut  are rated for the appropriate spindle rpm. Improper selection will cause spindle     bearing failure. ISO Tool Holder Collet and Spindle Definitions Collet Note: Only a completed collet and collet  nut  assembly  should  be screwed onto a tool holder. Collet Nut Router Bit Note: Always make sure the router bit  is  properly  balanced  for  the appropriate spindle rpm.  Improper selection will cause spindle failure. of the collet length. This type of collet grips the tool evenly over the entire length of the collet and tends to have more flexibility,  which  results  in  “ranged”  or  “universal”  collet sizes.  This  means  that  a  specific  collet  size  can  hold  a range of tool sizes (typically inch and close metric sizes). Collets are made from spring steel, and regular usage causes loss of elasticity and the need to replace them more often. It is recommended to use collets designed for specific size tools, as requiring the collet to expand for too-large tools or compress for too-small tools will shorten the life expectancy of the collet. Proper Tool Colleting Installation  of  the  tool  in  the  collet  and  collet  nut  is equally important. To prevent unnecessary strain on the collet and to ensure a proper fit, only use a collet designed to fit your tool shank diameter. In addition, the tool’s flute should not extend into the collet; doing so can score the inside of the surface, as well as force debris into the collet, putting  the  entire  assembly  off-balance  and  potentially damaging  the  spindle.  The  graphic  below  illustrates  the correct and incorrect installation. Please note that these illustrations are designed to show proper insertion of the tool into the collet, and do not show the collet nut. Half-Grip Collet Full-Grip Collet Cutting flute is outside of collet. Tool shank fills 80% of collet. CORRECT Cutting flute is inside of collet. Tool shank doesn't fill 80% of collet. INCORRECT