|Centring, Drilling and Counterboring / Countersinking - Course: Techniques for machining of material. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 22 p.)|
|1. Purpose of centring, drilling and counterboring/countersinking|
|2. Types and application of centring, drilling and counterboring/ countersinking tools|
|3. Preparation of centring, drilling and counterboring/countersinking|
|4. Centring with the centre square, centre bell and height gauge|
|5. Centring with the centre drill|
|6. Centring with the turning tool|
|7. Drilling with the drill and boring with the boring tool (turning tool)|
|8. Counterboring/countersinking with counterbore/countersink and turning tool|
Centring, drilling and counterboring/countersinking are metal-cutting operations with single-, double- and multi-edged cutting tools which are constantly in action. They are used to produce internal surfaces of rotationally symmetrical parts (rotating around their axis of rotation).
Figure 1 Inside machining of parts by centring, drilling, counter-boring/countersinking
1 centre hole,
2 drilled hole,
3 bored/counterbored hole
Centring is a cutting operation with primarily double-edged tool (centre drill) but also with single-edged tool (turning tool). It is used prior to other cutting operations, such as turning between centres, taper turning, drilling and grinding. The work-piece is fixed in a certain position (mostly central position) to the axis of rotation.
Figure 2 Centring on the lathe
1 drill chuck,
The main types of centre holes are centre holes types A and B. Type C (protected cylindrical centre holes) are rarely used. Drilling is like centring a cutting operation with single- or double-edged tool.
Drilled holes are required, for example, to locate screws, rivets, bolts, pins. shafts and other cylindrical parts.
Figure 3 Drilling on the lathe
3 twist drill
Counterboring/countersinking is a cutting operation with a multi-edged tool for the purpose of enlarging, boring, spot facing, deburring and chamfering drilled holes. Counterboring/counter-sinking is required, for instance, for inserting bolt, rivet and screw heads into a part.
Figure 4 Boring/counterboring with the turning tool
Figure 5 Counterboring with the piloted counterbore
Counterboring/countersinking is also used to produce plane seating surfaces for screw heads and other machine elements on castings with uneven surface.
Figure 6 Counterboring with the counterbore
What is the basic purpose of centring, drilling and