Technical SectionPhone: 516-328-3970www.technocnc.com11ColletsThere 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 fromPull StudNote: This is a maintenance itemand should be replaced every 6months. HSK Tool HolderN 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 HolderCollet and Spindle Defi nitionsColletNote: Only a completed collet and collet nut assembly should be screwed onto a tool holder. Collet NutRouter 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 ColletingInstallation 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 tools 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-GripColletFull-GripColletCutting fl uteis outside ofcollet.Tool shank fi lls 80% ofcollet.CORRECTCutting fl uteis inside of collet.Tool shank doesnt fi ll80% of collet.INCORRECT