To do rigid tapping on these machines would not work because the motor rpm and the z- feed rate have to be tied together precisely not to mention precise forward and reverse control. This would require a completely different spindle motor.
Non rigid tapping could be done but even then, you would need to know what your rpm's are. A tapping head with a lot of float might work but, personally, I wouldn't risk damaging an expensive tapping head.
I suggest buying a $75.00 hand tapper. They work great.