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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 identifi ed 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 fi ll the entire length of the collet. Full-grip collets have slits running up from Pull Stud Note: This is a maintenance item and  should  be  replaced  every  6 months. HSK Tool Holder N o t e :    A l w a y s make sure the tool holder  and  collet nut are rated for the appropriate spindle r p m .    I m p r o p e r selection will cause spindle  bearing failure. ISO Tool Holder Collet and Spindle Defi nitions 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. the bottom and down from the top, again for about 80% 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 specifi c 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 fi t, only use a collet designed to fi t your tool  shank  diameter.  In  addition,  the  tool’s  fl ute  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 fl ute is outside of collet. Tool shank fi lls 80% of collet. CORRECT Cutting fl ute is inside of collet. Tool shank doesn’t fi ll 80% of collet. INCORRECT