Page 67 - Turner 1st sem Practicals

Locating hole accurately by drilling centre hole

Objective: This shall help you to
• drill centre holes with a drilling machine.

Drilling centre holes by combination drills is an accurate Remove the centre drill, hold the twist drill of the required
method of locating the position of the holes (i.e within dia. check if it 'runs true'. start drilling the through hole.
±0.25mm). In drilling operations, this method will be
specially helpful while drilling deeper holes and holes of
fairly accurate locations. For doing centre drilling, proceed
as follows.
Hold the combination centre drill in the drill chuck and
check whether it 'runs true'. Adjust the spindle speed to
suit the combination drill.

Adjust the job together with the vice and align with the
centre punch mark.(Fig.1)
Drill a centre hole up to the depth of 3/4th of the counter
sink. Do not apply undue pressure on the centre drill.
Apply sufficient quantity of cutting fluid.

Producltion & Manufacturing : Turner - Exercise 1.2.19 55