Page 732 - Iscar

USER GUIDE
TAPS Tap Tolerances

Tolerance classes of taps and tolerance positions Nut thread Tolerance Nut thread
for screw threads as per ISO metric standard. positioning of classes for positioning of
H tolerance taps G tolerance
8H
7G
7H
6G
6H
5G
5H 4G
7G
4H
6G
6H
=0 4H
Tap tolerance Nut threads Au
according to Au
H tolerance
Basic Pitch Diameter
D2 D2
Au = Basic Deviation of Pitch

For Optimum Tapping Conditions, Reduced Machining
Times and Increased Tap Life

Selection of the Most Suitable Tap Tapping Speeds
As a general rule, materials with deformation capability of The tapping speed has a great influence on chip flow
at least 10% can be cold-formed. and the life of the tap.
To decide on the most suitable tap, please refer to the tap It is worthwhile to establish the ideal speed by
recommendation table on page 706. tapping trials.
For recommended initial values, see table on
Pre-Tapping Holes page 706. In addition, the following should be taken into
Check that the holes are within the prescribed size range consideration: characteristics of the material, machine
depending on the application (see table on page 720) The and clamping method.
holes should be clean and swarf-free.
Effects of Unsuitable Tapping Speed
Lubrication • forced tapping
Frequently the lubricant content of the coolant used for • tap lead chipping caused by overloaded cutting tooth
general machining is too low for tapping. • torn threads
• If it is not possible to increase the lubricant content, • unsatisfactory tap life
following are some possible solutions: • rejected threads
• A separate Iubricating unit can be connected to the
machine control, to deliver the required quantity of
concentrated emulsion into the core hole or onto the tap.
Tapping in separate operations allows the use of the ideal
tapping lubricant.

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