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  ROTATION SPEEDS FOR CORE BITS

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Diamonds cut best at certain speeds and since they are mounted on a circular bit face it is the peripheral linear speed that is most important. For a given rotational speed, the peripheral linear speed increases as bit diameter increases. The relationship is given by the following formula, where v is the peripheral speed, d the diameter of the bit and r the rotation speed:


Different types of bits have different ranges of optimum peripheral speeds:

  • Tungsten Carbide Bits 
  • Sawtooth Diamond Bits (Air Flush) 
  • Sawtooth Diamond Bits (Water Flush) 
  • Surface Set Bits 
  • Impregnated Bits  
    30-75 m min-1
    30-75 m min-1
    80-150 m min-1
    80-225 m min-1
    150-370 m min-1

    Using the above relationship, the following table relates bit diameter to speed of rotation for different bit types.

    This should be used as a general guide only and we advise the driller to experiment with different speeds in order to find the optimum. Generally speaking, the softer the rock, the slower the speed that should be used, and the bigger the diamonds the slower the speed. If vibration occurs it can sometimes be eliminated by reducing the speed.

     

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