MACHINE TOOL : Drilling Machine

(i) Producing a hole:

Drilling operation (Fig 1 mark ,explanation 2 mark) : It is an operation of producing a circular hole in a work piece by forcing a drill against it. It is the operation of producing a cylindrical hole by removing metal by the rotating edge of a cutting tool called the drill. Drilling hole not produce an accurate hole in a workpiece and the hole so generated by drilling become rough and the hole is always slightly oversize than the drill used due to the vibration of the spindle and the drill.

(ii) Finishing previously drilled hole:

Reaming operation (Fig 1 mark ,explanation 2 marks) :It is accurate way of sizing and finishing a hole which has been previously drilled. The speed of the spindle is made half that of drilling and automatic feed may be employed .Reamer cannot originate the hole .It simply follows the path which has been previously drilled and removes a very small amount of metal. It is an operation of slightly enlarging a machined hole to proper size with a smooth finish. The material removed by this process is around 0.375mm and for accurate work this should not exceed 0.125 mm