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		Centring, Drilling Counterboring and Countersinking, Reaming and Tapping on the Drilling Machines - Course: Techniques for machining of material. Trainees' handbook of lessons (Institut für Berufliche Entwicklung, 24 p.)
			(introduction...)
			1. Purpose of centring, drilling, counterboring and countersinking, reaming and tapping
			2. Kinds, construction and applications of drilling machines
			3. Kinds and construction of centring, drilling, counterboring and countersinking, reaming and tapping tools
			4. Clamping possibilities for workpieces and tools
			5. Preparation of work
			6. Centring, drilling and counterboring or countersinking
			7. Reaming and tapping

1. Purpose of centring, drilling, counterboring and countersinking, reaming and tapping

The techniques of centring, drilling, counterboring and countersinking, reaming and tapping serve to make internal rotationally symmetrical workpiece surfaces. They are cutting operations with single-edged multiple-edge tools which are constantly in action (single-edged tools as exception for making bores with boring bars).

Centring is applied for carrying out subsequent operations. Centring creates the conditions of fixing the workpiece in a certain position (mostly central position) to the tool axis. This cutting operation is carried out mainly with two-edged tools (centre drill), but also with multiple-edged tools (counterboring or countersinking). Centring can often be substituted by centre punching.

Figure 1. Centre punching by hand

Drilling is like centring a cutting operation with single-edged or two-edged tools (twist drill). A distinction is made between drilling and boring. Rotationally symmetrical through bores, stepped bores and blind bores are produced.

Figure 2. Kinds of bores (basic types)

1 through bore, 2 stepped bore, 3 blind bore

Counterboring or countersinking as cutting operation with a multiple-edge tool serves to remachine bores (deburring, chamfering, expanding).

Reaming is a cutting operation with a multiple-edge tool which is constantly in action. Bores of high dimensional accuracy and surface finish can be produced.

Tapping is a cutting operation with a multiple-edge tool (tap). Tapping provides a hole with a thread as non-permanent joint.

For what purpose are centring, drilling and reaming applied when internal rotationally symmetrical workpiece surfaces are machined?

Cent ring:
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Drilling:
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Reaming:
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