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close this bookDriling, Countersinking and Counterboring - Course: Technique for manual working of materials. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 18 p.)
View the document(introduction...)
View the document1. Purpose of drilling
View the document2. Machines for drilling
View the document3. Tools for metal drilling
View the document4. The operation of drilling
View the document5. Setting of the tools
View the document6. Clamping of the tools
View the document7. Clamping of the workpieces
View the document8. Technological process of drilling
View the document9. Purpose and application of counterboring/countersinking
View the document10. Labour safety recommendations

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?