Hi, Rick
Post the values for R1 & c1 when you get a chance, Happy it works.
The M05 should turn the Spindle Off, I don't understand exactly what your saying.
If you have a Dual Trace Scope, Look at the input & output Pulses.
With a 10 turn R1, You may be able to tweak for more Speed if needed.
The ability of Mach to have time see the delay pulse & the output pulse reseting before the next input pulse, Set the Speed Max Limit.
Thanks, Chip