Page 93 - CITS - Fitter Trade Pactical - Volume - 2
P. 93

FITTER - CITS




           •  Fix Ø 6mm drill in drilling machine spindle through drill chuck and drill pilot holes for both through and blind
              holes.
           •  Use soluble oil as coolants for drilling Mild steel workpiece .
           •  Fix Ø 8.5 mm drill and drill through hole as per drawing.

           •  Fix Ø 10.5 mm drill and drill blind hole to the required depth of 14 mm using depth stop of drilling machine.
           •  Use kerosene oil for drilling in Aluminum flat.
           •  File and de - burr in all the surfaces of the job.
           •  Apply a thin coat of oil and preserve it for evaluation.


           Skill  Sequence
           Job Sequence


           Drilling blind holes

           Objective : At the end of this exercise you shall be able to
           •  drill blind holes to the required depth using the depth stops.



           Method of controlling depth of blind holes
           While drilling blind holes, it is necessary to control the feed   Fig 1
           of the drill. Most machines are provided with a depth stop
           arrangement  by  which  the  downward  movement  of  the
           spindle can be  controlled. (Fig 1)

           Most depth stop arrangements will have graduations by
           which the advancement of the spindle can be observed.
           Generally the blind hole depth tolerances are given up to
           0.5 mm accuracy.
           Setting for drilling blind holes
           For blind hole - depth setting, first the work is held on the
           machine and the hole is located correctly.
           The  drill  is  started,  and  it  drills  until  the  full  diameter  is
           formed.  Note  down  the  initial  reading  at  this  point.
           (Fig 2)
           Add the initial reading to the depth of the blind hole to be
           drilled.
           Initial reading + Depth of hole = Setting.
           Adjust  the stop next   to the required setting, using the
           scale.
           Tighten the lock nut to prevent the setting from being disturbed.
           Start the machine and feed the drill. When the stop nut reaches the arm, the blind hole is drilled to the required
           depth. (Fig 3)

              While drilling, release the drill frequently from the hole for the chips to be flushed out by the cutting
              fluid.








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                                            CITS : CG & M - Fitter - Exercise 28
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