Page 62 - HOLE MAKING CATALOG p311-382

TAPS USER GUIDE

Tap Tolerances For Optimum Tapping Conditions, Reduced
Machining Times and Increased Tap Life
Tolerance classes of taps and tolerance positions
for screw threads as per ISO metric standard. Selection of the Most Suitable Tap
As a general rule, materials with deformation
Tap tolerance Nut threads according capability of at least 10% can be cold-formed. To
to H tolerance decide on the most suitable tap, please refer to
the tap recommendation table on page 346.
Nut thread Tolerance classes Nut thread
positioning of for taps positioning of Pre-Tapping Holes
H tolerance G tolerance
Check that the holes are within the prescribed
8H size range depending on the application (see table on
page 364) The holes should be clean and swarf-free.
7H 7G 7G
6G Lubrication
6H 6H 6G
5H 4H 5G Frequently the lubricant content of the coolant used
4H 4G for general machining is too low for tapping.

Au =0 • If it is not possible to increase the lubricant
content, following are some possible solutions:
D2 D2 Au
• A separate Iubricating unit can be connected
Basic Pitch Diameter to the machine control to deliver the required
Au = Basic Deviation of Pitch quantity of concentrated emulsion into the core
hole or onto the tap.Tapping in separate operations
allows the use of the ideal tapping lubricant.

Tapping Speeds
The tapping speed has a great influence on chip flow
and the life of the tap. It is worthwhile to establish the
ideal speed by tapping trials. For recommended initial
values, see table on page 346. In addition, the following
should be taken into consideration: characteristics
of the material, machine and clamping method.

Effects of Unsuitable Tapping Speed
• forced tapping
• tap lead chipping caused by overloaded cutting tooth
• torn threads
• unsatisfactory tap life
• rejected threads

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