On many modern CNC machining centres the rotation of the spindle can be synchronized with the feed axis. This makes it possible to produce threads with tool holders without length compensation. However, practical experience shows that even with this kind of "rigid tapping", synchronization errors can come up.

Possible causes are:

• machine dynamics, harmonization of spindle and linear drives, especially during the moment of changing the rotation direction
• play in the tooth flanks in the driven tool holder
• play in the drive between driven tool holder and machine drive
• tolerances on the threading tool

When rigid tool holders are used, these errors can lead to problems. High axial forces come into play, and can have serious negative consequences on the production process, such as:

• reduced tool life, caused by high one-sided flank friction on the threading tool
• unclean thread flanks on the workpiece
• threads not true-to-gauge

heimatec collet holder softtap for driven tools

• serve as absorbing link between synchronous spindle and tap / cold-forming tap, and compensate pitch differences between threading tool and drive
• provide the high concentricity of a rigid tool holder
• guarantee safe clamping of taps / cold-forming taps by collets with square drive
• do not necessitate tools with special shanks
• guarantee process safety in the synchronous production of threads

Constructional details

• made of two pieces (holder shank / tool seat)

-        easy to disassemble

-        allowing trouble-free maintenance

• axial force compensation and torque are separated

-        hardly any influence of torque on axial force compensation

• absorption elements made of plastic

-        no influence on the cutting edge of the tool through axial vibration during work

• pre-tensioning of absorption elements

-        allowing axial movement only after the pre-tensioning force is exceeded

• axial movement guided by balls

-        reduced friction (rolling friction), and consequently extra short reaction times

• suitable for up to 70 bar internal coolant-lubricant pressure

-        no effect on axial force from coolant-lubricant pressure, consequently no axial movement

Practical application

Many tests regarding this topic have been made with taps and cold-forming taps. Depending on the individual case, our customers were able to increase their tool life by up to 150%. In the following diagram, you will find the axial forces which come into play in the cold-forming of an M10 thread in St37.

We have traced the axial forces at a speed of 2000 rpm.

The following collet holders were tested:

• a) rigid synchronous collet holder
• b) collet holder Softsynchro® size 01, with minimum length compensation on tension and compression
• c) synchronous collet holder of a competitor with minimum length compensation with axial absorption

All tested collet holders were used with a collet type ER16-GB, i.e. with integrated square.

Axial force [N]                                                                                               Speed      2000 rpm

Time    [s]

The following results were verified in these tests:

• axial forces increase with the increase of speed
• the forces which come into play in the cold-forming of threads are considerably higher with a rigid collet holder than with an collet holder softtap
• the competition collet holder can absorb the upcoming forces only lightly, in comparison with the rigid collet holder

Conclusion

The collet holder softtap makes the optimum use of driven tool holders in the production of threads possible, with the best imaginable tool life and thread surface quality.