I have searched the various topics regarding spindle control and the software issues involved with GRBL. I am using Blackbox motion controller through my MacBook Air. My spindle is a DW611 running through an IoT relay, connected to the tool head out on the Blackbox. With Open Control, the connections were PWM and GND to switch the IoT, but with Easel, I had to switch the power lead to 1-10V from PWM. That said, I can only control the spindle during set-up. It fails almost every time when I get ready to cut, and have to manually operate the spindle through the Normally On outlet on the IoT. I fiddled around with the GRBL console, and was able to get the spindle to switch on and off using the M3 and M5 commands, sometimes with no speed reference on M3, but most often having to input an S command of 2323 or higher. M3 S2322 would result in no spindle, M3 S2323+ would switch the spindle on. This was with $30=10000, $31=1, and $32=1. I am out of ideas.
Change $32=1 to $32=0
Setting $32 controls operation of the “spindle” over to “laser mode” and is not used in your case.
$32 - Laser mode, boolean
When enabled, Grbl will move continuously through consecutive G1 , G2 , or G3 motion commands when programmed with a S spindle speed (laser power). The spindle PWM pin will be updated instantaneously through each motion without stopping. Please read the GRBL laser documentation and your laser device documentation prior to using this mode. Lasers are very dangerous. They can instantly damage your vision permanently and cause fires. Grbl does not assume any responsibility for any issues the firmware may cause, as defined by its GPL license.
When disabled, Grbl will operate as it always has, stopping motion with every S spindle speed command. This is the default operation of a milling machine to allow a pause to let the spindle change speeds.