Hi, thanks for your interest in the UCCNC.
The index prescaler for the spindle can be an integer value and the limit is the 50kHz counting frequency, becaus the signals are polled with 100kHz.
Although the index prescaler can be used only to count the spindle speed more precisely than with a single slot encoder.
The 1.1 version of the software can also do rigid tapping and syncronous thread cutting with free running spindle with encoder feedback.
for that you need an incremental encoder with A,B and Index channels.
The index channel must give one signal per turn, so there should be no gearing between the encoder and the spindle shaft, or if there is then the index must be placed to the spindle shaft (e.g. an optical gate and a half disk on the spindle shaft.)
Also the index must be at least 10microsec long to be read safely by the UC100/300.
For the encoder the frequency limit is the same, 100kHz sampled, so 50kHz max. if the encoder channels are perfectly aligned to 90°,
this means 3000 1/min max. speed with a 1000 pulse per rev encoder which is probably enough for all applications since nobody really want to cut a thread or tap a drill with so high spindle speed.
Also the threading and tapping algorithm looks ahead and it calculates the angle ahead based on the actual rotational speed and it counts sub-encoder ticks, so it's quite precise with even a 100 counts encoder.
The 1.1 version is not public yet, because we still want to do a few more things before releasing it to the public, but if you PM me your e-mail address then I'll e-mail you the download link for the latest non-official release.