spindle with encoder

Hold on a second. I lied. Not intentionally. My spindle motor is a DYN4 servo motor geared 1:1.8 and it has a simulated encoder signal generated by the servo driver. That is the signal I am using for the coordination for rigid tapping. The sensor on the slotted plate it just for measuring RPM.
It's been a few years since I set this up and when you mentioned more slots I thought "I knew that, why didn't I do that?" Then I looked deeper and remembered how it really works.

To actually do this with a slotted plate and sensors you would want more slots and two sensors. Read up on how quadrature encoders work.

As long as you know the ratio between the spindle and encoder you can make almost any arrangement work.

These are my .ini settings.
[SPINDLE_0]
P = 2.0
I = 4.0
D = 0.0
FF0 = 1.08
FF1 = 0.0
FF2 = 0.0
BIAS = 0.0
DEADBAND = 0.0
OUTPUT_MIN_LIMIT = -5400.0
OUTPUT_MAX_LIMIT = 5400.0
OUTPUT_SCALE = -10800
ENCODER_SCALE = 4551.111111
#((2048 * 4) / 1.8) = 4551.111111
#The maximum spindle speed (in rpm)
MAX_FORWARD_VELOCITY = 5400
#The minimum spindle speed (in rpm)
MIN_FORWARD_VELOCITY = 50
#This setting will default to MAX_FORWARD_VELOCITY if omitted.
MAX_REVERSE_VELOCITY = 5400
#The minimum spindle speed (in rpm)default to MIN_FORWARD_VELOCITY if omitted.
MIN_REVERSE_VELOCITY = 50

Sorry for the confusion. I hope this helps.

This helps..
What is OUTPUT_SCALE = -10800 ?
This config is for fixed motor:spindle transmition ratio.
I have 2 selectable speeds after encoder-motor
These 2 speeds are selected by hydraulic electrovalve that switches gears
position 1 max rpm is 760rpm and position 2 max rpm 3060