22
1 7.2
SHEET METAL DRILLS
(with center tip)
Grinding wheel: Corundum, dress the right side of the wheel with an angle of
approx. 45°
.
Use the grinding wheel dresser to dress the requested shape.
Adjustment of drill
Prism rest
Adjustment of the drill in the prism:
•
Adjust the main cutting edge parallel to both graduation line on the prism (see pic.)
•
Project the drill around
35 40 mm
outside the prism
Adjustment of the machine:
•
Top angle: 1 80° left
•
Clearance angle: to your requirement
Grinding operation:
By carefully feeding the prism towards the wheel and meantime swivelling the prism,
grind the first side of the cutting edge, then move with the motor feed to the centre tip of
the drill bit and grind over the tip using the
45°
dressed side of the grinding wheel.
Note the No. on the scale of the prism feed and move back, remove the prism of the
prism support, reverse, fix again in the support and grind the second cutting edges to the
same graduation No. Now the second side of the tip is ground centrically.
The tip thinning is identical as for twist drills (see page 1 8).
