Page 172 - Industrial Tools Catalog (1)

Thread tools \ Technical introduction – thread tapping
CARBO Vaporisation
A new type of special coating for high-perfor- CARBO This is a chemical surface treatment rather than a
mance machining of non-ferrous metals (alumin- classic coating.
ium alloys, wrought alloys), which are character- This steam treatment ensures that the lubricating
ised by good emergency running properties and film on the screw tap surface does not tear off
low edge build-up formation. during tapping.
ƒ Vickers hardness: 6000 HV
ƒ Friction coefficient: 0.1
ƒ Temperature resistance: 700°C
ƒ Colour: Black

Thread types and thread depths when tapping

In thread machining, we distinguish between through holes and blind holes. The blind hole places the most demands on a screw tap, as the chips in long-chip-
ping materials have to be transported upwards out of the hole and must be broken at the changeover point. As a result, spiralised screw taps must be used with
long-chipping materials.
A spiralised design is not necessary with short-chipping materials, as the short chips fall into the blind hole and are rinsed out by the coolant.
As a rule, a thread depth of 3xD can be achieved in blind hole machining, depending on the material. maximum process reliability is achieved but with thread depths
up to 2.5xD.
Through holes can be made with thread depths of up to 4xD. Here too, for process reliability can be expected for 3xD.
The through hole is a relatively non-critical process, as the chips are removed in the direction of feed. The chips are removed either through a spiral point or a left-
hand spiral. Screw taps designed for both blind and through holes are another consideration. However, these only work with short-chipping materials or very low
thread depths.

Blind hole machining Blind hole machining Through-hole ma- Through-hole Blind hole and
with spiralised screw with straight- chining with left-hand machining with spiral through-hole ma-
tap in long-chipping grooved screw tap spiralised screw point in long-chipping chining with straight-
materials in short-chipping tap in long-chipping materials grooved screw tap
materials materials

2,5xd 3xd 2,5xd
Max. thread depth 2.5xD of blind hole Max. thread depth 3xD of blind hole Blind and through-hole machining with straight-
(e.g. M6 = max. thread depth 15 mm) (e.g. M6 = max. thread depth 18 mm) grooved screw tap
(e.g. M6 = max. thread depth 15 mm)

Cutting point shapes and their function

on a screw tap, the point plays an important role in the thread cutting process and is decisive when it comes to service life and thread quality.
We distinguish between the following five point shapes. Apart from point shape B with a spiral point, which is only a straight-grooved shape, all other point shapes
can be combined with the different chip flutes.
In principle: Longer points mean a longer service life. This a particular advantage at high quantities. However, the required torque also increases, producing higher
forces. Short point shapes enable the thread to be cut nearly to the base of the hole.
Common point shapes are B, C and E.

Long, 6–8 turns
for short through holes
A (6-8)

Medium, 3.5–5.5 turns
with spiral point, for all through holes and large thread depths in medium- and
B (3,5-5) long-chipping materials

Source: Hahn+Kolb Werkzeuge GmbH
172 Technical data subject to change. www.iconridge.com
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