tapping on cnc

[gbpacker]

i was wondering how you tap on a cnc without breaking the tap. i am new with cncs and have mostly manual machining experience. when i tap on a manual mill i just start the the thread in the machine and then tap it rest by hand to prevent breaking the tap off in the hole. i was just wondering what is the best way to tap using a cnc.

[christinandavid]

Hi,

If your machine has basic tapping cycle hold the tap in a floating/compression tapping head. You must program your feedrate bearing in mind the pitch of the tap and your spindle speed. Depending on how critical your thread is/material you are tapping/tapping head type you can either program feed rate at the basic - speed x pitch - or you can adjust this feedrate by 10% to put pressure on the tapping head.

If your machine has rigid tapping capability ie it can synchronize the spindle orientation to axis movement, then you can hold the tap in a rigid tapping head (or even standard collet if you are brave). The rigid tapping cycle will calculate your feed rate automatically.

Keep everything CLEAN! Use a spiral flute tap to tap blind holes. Use cutting oil rather than coolant if practical. Do some test holes before you tap a critical part. Depending on the situation (material/tooling/tolerance/quantity) you may choose to merely start the hole on the CNC with a spiral point tap and finish it off by hand later. Many a time I have looked at a job with a broken tap in it/ripped up hole and thought 'If only....'

DP

[Al_The_Man]

In spite of the fact the Z axis is geared off the spindle shaft encoder, the spindle motor control also has to be under close control of the spindle controller.
Just gearing off the encoder in itself using a sloppy style spindle control does not really give the proper performance and can result in broken taps etc.
Generally spindle controller/motor combo's that can come close to servo control is required.
i.e. Pulse wheel or encoder on the motor to drive.
Al.

[Neal]

The rigid tapping is keyed of the spindle magnet hall effects switch and NOT the spindle motor encoder!

Neal

[Al_The_Man]

Originally Posted by Neal The rigid tapping is keyed of the spindle magnet hall effects switch and NOT the spindle motor encoder! Neal

Thats odd setup, Must be unique to Fadal, The method I referred to was the common practice of gearing off an encoder on the final spindle shaft, not the motor encoder.
A hall effect switch arrangement would also work but would not have the higher resolution afforded by a optical encoder.
Al.

[Neal]

The spindle encoders do not have any index mark. Therefore both the Fanuc and Fadal controls use to embedded magnet in the spindle pulley to orient the rigid tapping.

Neal

[Techman]

For me rigid tapping is the the best invention since sliced bread. I have tapped loads of holes with our Fadal and to date the only taps I have broken are one that I programmed the wrong pitch and another that the tap drill broke first then of course the tap had to do the same!
Good luck.
Jim