G04 Dwell option

[martin 321]

Option to set G04 dwell in Gcode creation, for spindle to get up to speed before milling starts.

[Juan Pablo Caram]

From the standard:

3.5.4 Dwell — G4
For a dwell, program G4 P… . This will keep the axes unmoving for the period of time in seconds
specified by the P number. It is an error if:
• the P number is negative.

[Juan Pablo Caram]

I guess this would be required at the start and after every tool change, right?

[Juan Pablo Caram]

Cleaned up G-code parser. Fixed dwell command. Fixes #184.

→ <<cset d1442a49008d>>