36
Only bits with symmetrical tips can drill holes at the desired position, and you must therefore
finish by fine grinding both blades a few times until there are no more sparks, and without
performing tightening actions using the adjustment screw (7).
10.4 Angle of the bit
Angle of the tip:
The bit grinding unit is for grinding bits with tip angles of 116-118°,
which are those most frequently used. The angle of the tip cannot be
changed by adjusting the bit grinding unit
.
Chisel edge angle:
Perform grinding so that the chisel edge angle is approximately 55°.
See Fig. II
Clearance angle:
Generally speaking, the clearance
angle should be 6-8°. See Fig III. As
stated previously, it will be larger if
the stop is more than 1-1.5 mm from
the grinding wheel. If the clearance
angle is to be changed, the arm can be adjusted using + or -.
For bits over 25 mm it may be necessary to reduce the length of the chisel edge
(see Fig. IV), as a large chisel edge places a large load on the drill.
Always keep the V-groove as clean of grinding dust as possible.
Ensure there is good working light.
Follow standard safety rules and regulations for grinders. Avoid unnecessary heating of the
bit tip when grinding, e.g. by keeping the grinding wheel true and using a visible grain.
10.5 Using a diamond to true the grinding wheel
Loosen the Allen bolt (19) and tighten the locking screw (17). Loosen the nut (13) and use the
round finger nut to set the stop (8) for the bit to approximately 5 mm from the grinding wheel.
Loosen the adjustment screw (16) for the clamp, and lay the holder containing the diamond in
the V-groove. Push the clamp carefully forward to touch the diamond holder, until the
diamond is approximately 2 mm from the grinding wheel.
Tighten the adjustment screw (16) again. Start up the machine. The arm can now swing
towards the centre.
True the side of the grinding wheel with very little tightening of the diamond using the
adjustment screw (7). Continue truing until the wheel is completely clean and smooth. Take
care not to let the diamond touch the flange or nut at the shaft end. Once the diamond is
removed you can prepare for bit grinding.
10.6 Grinding wheel
A cup wheel must be used. Grain sizes in the range 36 to 60 are recommended, of normal
corundum or precious corundum as required.