Page 45 - CITS - Fitter Trade Practical - Volume -2
P. 45

FITTER - CITS


           Skill Sequence

           Counter sink

           Objectives: At the end of this exercise you shall be able to
           •   countersink holes of different sizes.


           Selection of countersinks
           Select the countersink tool according to the angle of the taper head of the screw. Use the table for countersink
           holes.
           Fix the job in the machine vice (if necessary, use parallel blocks) and set it square.
           Align the machine spindle with the drilled hole to be countersunk. (Fig 1)

              Fig 1












           Remove the drill and fix the countersink tool on the machine without disturbing the alignment. (Fig 2)
           Set the spindle speed of the drilling machine RPM. Use the formula

               Fig 2



















           Substitute the recommended speed of the countersink.

           (V = 1/3rd of the cutting speed for drilling)
           Countersink hole to a depth equal to the head length of the screwhead. (Fig 3)

               Fig 3


















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                                            CITS : C G & M - Fitter - Exercise 62
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