M84 is rigid tapping, and it is done only by a CSMIO/IP motion controller as a fully autonomous feature. During rigid tapping in Mach3, the Z-axis position is synchronized with a current spindle position. The synchronization is fast and so precise that you have a feeling that the spindle is connected to the Z-axis mechanically. It’s very important, and this should be clearly stated that the synchronization lasts continuously through the entire rigid tapping process. With it, at the bottom of the hole, where the spindle changes revs direction, there will be no “tension/compression” (stretch/squiz) situation. It protects the tap from breaking.
It doesn’t matter if you are using a VFD or a servo drive for spindle driving, and it’s important that the spindle has sufficient torque.
G4/G74 is standard tapping where you can use either a VFD or a servo drive.
The CSMIO/IP controller’s role is to synchronize trajectory set by Mach4 with spindle rotational speed. To simplify, we can say that the Z-axis feedrate is synchronized with spindle rotational speed. The synchronization isn’t perfect like in the case of Mach3, but in practice, it works and doesn’t cause significant issues. However, the problem is that we have the “tension/compression” situation at the bottom of our hole when the spindle changes direction.
It happens because Mach4 does not include that a spindle must rotate several times before it brakes and accelerates to the opposite direction. Because of this, you need to use a compensation tapping head to eliminate it.
Mach4 manual mentions it:
“Due to slight variations of spindle speed, feedrate and accelerations in some machines it is recommended that a special tapping head be used. A tapping head allows the tap to float a little bit, compensating for those variations, especially at the bottom of the hole.”
– G84.2/G84.3 is rigid tapping for which Mach4 manual says:
“requires the machine to have precise control of spindle speed, axis feed, and precise feedback of spindle RPM.”
It means that for spindle driving, you should use a servo drive that can keep a set position. It can be a step/dir drive (supporting position mode) in the case of CSMIO/IP-S controller or +/-10V (velocity mode) in the CSMIO/IP-A motion controller.
Further, Mach4 has the “Enable Step/Dir Spindle rigid tapping” option, which you may think should treat a spindle as a rotary axis. It means that even without synchronization provided by a CSMO/IP controller, rigid tapping should be possible because the spindle has become a full-fledged rotary axis. Unfortunately, it’s not like that. ArtSoft informed us (a few months ago) that it would be corrected. (as of 02/16/2022).
Our developers plan to release a plugin update for Mach4 soon that includes the rigid tapping as well if:
- we get documentation of newly added functions and changes in Mach4
- newly added functions and changes made in Mach4 will work as assumed.
- we get explanations for questions we may have.