Hey everyone,
Got stumped once too many times with feeds / speeds not matching observed results…
…so I built a tachometer with an ESP32 counting IR light pulses.
Results seem to indicate my A350 give me the following speeds ( at no load )
M4 P100 = 11940 to 12000 RPM ( fluctuating across 1min of measurements )
M4 P90 = 10800 to 10860 RPM
M4 P80 = 9600 to 9660 RPM
M4 P70 = 8400 to 8460 RPM
M4 P60 = 7140 to 7200 RPM
M4 P50 = 5940 to 6000 RPM
Please note:
I have not verified functionality of code + ESP32 + IR sensor…but numbers seem to make sense.
I hope this is helpful to someone 
ALSO…FUSION 360 GCODE exporter seem to always set the spindle speed to max speed ( M4 P100 ) regardless…so be prepared to edit the file manually…until that get fixed… ( snapmaker team I’m looking at you guys now… )
Cheers
//O.