spindle with encoder

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I see.

I suppose this is a low-speed spindle?

(not 10000RPM)

PCW wrote:

Just wait a second after the motor starts before reading RPM from encoder.

This would not work with rigid tapping (the OP's question)

The spindle starts before the tap is in contact with the work, correct?

Isn't the spindle RPM selected exactly by the VFD?

A 3-phase motor does not lose steps.

I think maybe you don't understand how rigid tapping works.


When rigid tapping, the Z axis motion is synchronized (geared basically)
to the spindle rotation, the synchronized motion is continuous through
the downstroke, spindle reversal and upstroke. Any pause that interferes
with this "gearing" will break taps.

rigid tapping needs reversal of spindle so backlash matters.
If i have encoder on spindle shaft backlash
will be problem?
How many lines encoder needed for rigid tapping?

For more than 1 line, you should buy a precision-made encoder wheel to ensiure accuracy.

Why if i put in spindle shaft an aluminum disk with 2x100 holes(pi/2 equally spaced for A- and 1 hole for index drilled on the same mill?
I think i can do holes 1-1.5mm in the same mill accurately.

Typically you just have one track of holes and the B detector offset from the A detector by
hole_pitch*(N+1/4). That is, if the holes were 2 mm apart, the A/B detectors would be
spaced .50 MM or 2.50 mm or 4.50 mm etc.

This 1/4 pitch offset gives you the desired 90 degree phase difference between A and B.
Note the when drilling holes you should aim for a 50% duty cycle waveform
on A and B. This may require some experimentation and changing  the sensors
radial positions.