Page 145 - Turner 1st sem Practicals

Job sequence

• Hold the square plate on 4 jaw chuck. • Select and set correct rpm.
• Setting the job for 4 jaws adjust equal distance of • Locate the guide pin to guide hole if job and carriage
reference concentric circle line. locked rigidily.
• Mount the drill chuck to tail stock spindle. • Move the compound slide giving gradual depth.
• Hold the Ø10mm drill to drill chuck. • Make a bore size Ø70mm in 6mm length.
• Through the pilot hole 10mm. • Stop the machine and remove inner piece.

• Set the trepanning tool make a bore size 70mm, tool • Trepanning tool is withdrawn carefully.
adjust and set centre axis to tool cutting point 35mm. • Check the dimension
• Clamp the tool holder in correct position and centre
height.

Skill sequence

Trepanning operation done on a Drilling machine The carriage is locked to the bed at the time of feeding the
tool by the compound slide hand wheel. To avoid the curled
Trepanning is the operation of producing a hole by removing
metal along the circumference of a hollow cutting tool. (Fig chips getting clogged, it is better to clamp the tool with its
1) The trepanning operation is performed for producing cutting edge upside down, with the direction of rotation of
large holes. Fewer chips are removed and much of the the workpiece being reversed.
material is saved while the hole is produced. The tool may Trepanning on lathe is successfully done on very thin
be operated at higher speeds as the variation in diameter sheets which are cut to a definite size and to the same bore
of the tool is limited by the narrow cutting edge. The tool diameter. The inner discs that form as waste will be useful
resembles a hollow tube having cutting edges at one end for some other applications. It is important to take the
and a solid shank at the other to fit into the drill spindle. this sheets together after properly aligning the edges so that
is one of the efficient methods of producing a bigger hole to when they are separated after the trepanning operation, the
a limited thickness. hole produced in each will be of uniform size and will be
uniformly located from the edges.
If the dimensional accuracy and surface finish of the hole
thus produced are to be of the high degree, a light cut of
about 0.1mm, with a fine feed rate of 0.05mm/rev may be
given and the hole may be bored. The pieces are separated
by the removal of tacking after the operation is completed.
The shape of the trepanning tool, the individual component
and the taked pieces held in the chuck are illustrated in the
Fig 2.

Trepanning operation done on a lathe
One of the special operations performed on a centre lathe
is trepanning. The lathe should be rigid in construction to
carry out this operation. The tool resembles that of a
parting off tool with secondary front clearance. The tool is
clamped in the tool post with its axis parallel to the lathe
axis. Its cutting edge is positioned with the outer edge to
contact the workface at a distance from the centre of the
workpiece atleast about 0.1mm less than the radius of the
hole required on the work. This is done with the help of the
cross-slide hand wheel and graduated collar. The lathe is
set to a spindle speed determined by taking 1/3 of the
cutting speed recommended for boring.

132 Producltion & Manufacturing : Turner - Exercise 1.3.41