9. Purpose and application of counterboring/countersinking
By counterboring/countersinking, bore holes are deburred,
precast or predrilled holes are enlarged or their rims worked in such way a that
screwed or riveted joints can be made.
Figure 16 -
Counterboring/countersinking
For this purpose, attention has to be paid to the following:
- Before counterboring/countersinking, the bore hole
must be brought in line with the working spindle.
- Work at a low rotational speed (approximately 350 r.p.m.),
otherwise there will be uneven surfaces.
Figure 17 - Types of
counterbores/countersinks
1 - Countersinking cutter (60°; 75°;
90°)
2 - Flat countersink
3 - Counterbore with spiral flutes
4 -
Counterboring tool with pilot or spot facer
5 - Form counterbore (special
forms)
9.1. Use of the counterbores/countersinks
- Countersinking cutter 60°:
Spot-facing of bore holes in which threads shall be cut (Nominal
measurement: Ds = N)
- Countersinking cutter 75°:
Spot-facing of bore holes for countersunk-head rivets
- Countersinking cutter 90°:
Spot-facing of bore holes that shall be reamed (Nominal
measurement: Ds = N + 0.2 mm) as well as spot-facing of bore holes in
which countersunk screws shall be fitted
- Flat countersink
Spot-facing of flat seating faces for screws on uneven surfaces
- Counterbore with spiral flutes:
Boring of predrilled holes by a small measure (Example: from 8
mm to 10 mm)
- Counterboring tool with pilot or spot facer:
Spot-facing of cylindrical screw head location. Pay attention to
the guiding clearance of the pilot of 0.05 mm - 0.1 mm. (Also possible by a
drill with flat drill point and centre point),
- Form counterbore:
Deburring and forming of irregular or curved pockets; for this
purpose, also rotary files or small form cutters are used.
What has to be taken into consideration when
counterboring/countersinking?
________________________________________________________________________
________________________________________________________________________
When do you use a 90° countersinking
cutter?
________________________________________________________________________
________________________________________________________________________
What are the fields of application of form
counterbores?
________________________________________________________________________
________________________________________________________________________
