by spumco » Tue Dec 27, 2016 5:22 pm
My spindle encoder is now installed and functioning, more or less.
Encoder is a Photocraft HS-20 100PPR model, with A/B/Z quadrature signals. 5-26VDC differential line driver output circuit with the A+/B+/Z+ signals going to my VFD, and the A-/B-Z- signals going to my breakout board as inputs to UCCNC.
My motor pulley is 54 teeth and the spindle is 36, so I've had to set the pulley ratio in UCCNC to 0.75:1. Setting it to 1.5:1 resulted in some hair pulling on my part. Duh.
My next questions for CNCDrive:
1. The commanded (Sset) speed doesn't match the displayed (Sact) speed. At Sset = 1000Rpm, Sact = 1170Rpm. I thought UCCNC would adjust the PWM to bring the actual speed closer to the commanded speed. Do I need to adjust the trim pot on my spindle control board, or does it not matter because for rigid tapping UCCNC will base the Z-axis motion on the Sact and not the commanded speed?
2. The Sact speed doesn't match the measured spindle speed. Using a strobe tachometer on the spindle, there is a difference of about 150Rpm. For example, if I set Sset = 3500Rpm, Sact = 4069Rpm, but the strobe measures 3917Rpm. Any idea, aside from the strobe not being accurate, why there is a difference between displayed and measured spindle RPM?
Thanks,
Spumco