Hi
I am having problems where the M3 command does not set any output on Mach3. Sometimes it will work first time and always and other times it will do nothing. Not when I use the Spindle icon or a MDI command.
If I enter a spindle speed manually it shows -1  and then does not start obviously.

If I go into the setup and change nothing but use apply, it will switch the spindle on when the M3 is issued.

Is it not starting because the speed is 0? How are you manually setting the speed. You should use S### in MDI to manually set the speed.

Not when I use the Spindle icon or a MDI command.

Does this mean it works with the button or MDI, or it doesn't work?

If it didn't work at all, I would guess a corrupt M3.m1s file. Some people seem to get this issue a lot.
But because it's random, I don't think so

Hi Gerry
The whole process is rather random and I am having a hard time to figure out what the correct sequence might be.
If I try and set the speed in the spindle speed box at startup it does not take it but the speed will change when I use the MDI S*********x.

I have the M3 set at output one and M4 at output 2. Sometimes the gcode (m3) will cause the spindle to turn CCW and sometimes it will turn CW. Now I have output one for both CCW and CW and then it will turn CW always.

It would seem that if I start a gcode file from scratch without any manual intervention it works mostly but if I try and run from line, it does not set any output even if I selected the spindle to be started. The icon comes on but no output.

If the speed was set with S********* and I click the M3 icon, it does not always start.

Not very sure of exactly how it works (or not) but this is as far as I can gather. If you want me to look at anything specific or any sequence, let me know what to test.

I would take a good look at  your wiring, and electronics. The only issue I've seen with Mach3 is that the spindle will not start at all. I don't think it's a software issue.