Using Collets in your Machines

By: Gord Thorogood

Collets are commonly used in a number of machines to either hold the work or hold the cutter. The purpose of a collet is to hold some thing accurately on center and allow rapid opening and closing within a very narrow size range. Collets operate by drawing the tapered collet into a tapered spindle using a draw bar or tube. The collet has a nominal size such as 1/2" and the object being held must be of that size. The holding capability decreases with every thousandth of an inch. The material is smaller or larger that the collet size. The tapers used for collets had been generally free tapers such as the “C” series and the R-8. These tapers are activated by the draw bar or tube and will instantly open when the draw bad is loosened. Collets with Morse tapers require a different perspective when operating.

Morse tapers are designed to be a holding taper which means that the collet will not open when the draw bar is released and the taper will hold just as it will in a drill press when you use a taper shank drill. The Morse taper collets usually have to be tapped out with a mallet. As you can see, if the drawbar is tightened as is required for the “C” collets or R8 the Morse tapered collets would be so outer tightened as to distort their shape which would decrease their holding capacity and they also would be extremely difficult to release. Avoid these conditions and you will find these collets to perform very well.

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