Spindle encoder selection (Mill)

Looking for some additional information about selecting a spindle encoder for rigid tapping. Been searching for a couple of days for the info. I have the mill up and running with a mesa 5i25/7i76 combo and I would like to know spindle rpm. Figure its cheaper to setup the spindle encoder instead of buying a tach tool.

From what I have gathered.
Encoder needs to be greater than 1 ppr and have a index pulse.

jmelson wrote:

machete wrote:

I can't imagine rigid tapping with anything less than 25 pulses/rev
which would give 100 quadrature counts per rev. You also
need an index so it makes it happy for multiple-pass threading,
although this is not strictly necessary for rigid tapping.

Jon

Would some mind filling in the extra info.

Pulse per revolution min?
Quadrature?
Voltage?
incremental or Absolute?
Analog or Digital?

Just to try to be complete for the record, a spindle encoder should have
some reasonable number of "lines" or "pulses". I would think 25 is
about the minimum, and 100 is quite satisfactory. Due to the high
pulse rate, it is not a great idea to use the software encoder HAL
component to read the spindle encoder. If you want to do that, you
need to carefully calculate the encoder count rate at the highest
spindle RPM and make sure the BASE_THREAD is fast enough
to read that. So, if you want 3000 RPM and have a 100 pulse/rev
encoder, that will give 400 counts/rev. 3000 RPM is 50 RPS,
so that is 400 * 50 = 20,000 counts/second, or 50 us between counts.
I would recommend the BASE_THREAD be half that to allow for
noise and timing variation, so that would be 25 us, or 25000 ns.

If that is a problem, then it would be strongly recommended to
use a motion controller with hardware encoder counters. The
Mesa and Pico Systems boards should all be able to do this.

The encoder should have digital outputs, and be of the incremental
type with an index pulse. Analog encoders would need some kind
of signal conditioner to convert the signals to digital.

Jon

Thank you both for the quick replies.

Might be a good addition to the man page about spindle encoder setup.