Threading Development

I have added spindle sync threading (G33) for the Arduino Mega GRBL-L-Mega and the Arduino Uno GRBL-L grbl controller:

• using an index pulse to start the thread
• using optionally synchronization pulses (spindle speed encoder pulses) to better compensate for spindle speed changes
• using the current GRBL input pins (Y-Limit and Probe) so existing GRBL shields can be used.

This spindle sync threading solution is supported by my CNCL software and tested using UGS platform. GRBL-L and GRBL-L-Mega can be used with "any" other GRBL Gcode sender.

GRBL doesn't support threading. There are some GRBL GUI's (CNCL and grblgru) that support threading by using a stepper for driving the spindle . This works very well but it takes some effort to implement.
There is a GRBL-Mega fork fschill grbl-Mega spindle sync that has implemented threading (G95) by using spindle speed encoder pulses to synchronize. Based on this version I have implemented spindle sync threading,