openscad -o stl/spoil_board.stl -D 'file_type="stl"' src/simple_spoil_board.scad

Inital box was created with Box Maker for InkScape. Then the 2d projections as dxf files were imported in Inkscape to arrange the box layout.

as per settings on stepper controllers:

• MICROSTEPS 8
• STEPS_PER_REV 200.0
• MM_PER_REV 8.0

steps_per_mm = (STEPS_PER_REVMICROSTEPS)/MM_PER_REV 2008/8 = 200

$0=10 (step pulse, usec)
$1=25 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=2 (dir port invert mask:00000010)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.020 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$14=1 (auto start, bool)
$20=1 (soft limits, bool)
$21=0 (hard limits, bool)
$22=1 (homing cycle, bool)
$23=3 (homing dir invert mask:00000011)
$24=50.000 (homing feed, mm/min)
$25=2500.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=200.000 (x, step/mm)
$101=200.000 (y, step/mm)
$102=200.000 (z, step/mm)
$110=5000.000 (x max rate, mm/min)
$111=5000.000 (y max rate, mm/min)
$112=1000.000 (z max rate, mm/min)
$120=500.000 (x accel, mm/sec^2)
$121=500.000 (y accel, mm/sec^2)
$122=200.000 (z accel, mm/sec^2)
$130=145.000 (x max travel, mm)
$131=120.000 (y max travel, mm)
$132=200.000 (z max travel, mm)

$G
[G1 G54 G17 G21 G91 G94 M0 M5 M9 T0 F50.]

[G0 G54 G17 G21 G90 G94 M0 M5 M9 T0 F0.]

These descriptions were taken from LinuxCNC G-code ref

This is a fixed position saved from restart to restart. It is used as a zero position for a part. So if there is a fixture that you want to start from use this. This is related to G92 (change the current coordinate system to the current tool position).

Description of Work Coordinate System for Grbl

Which plane arcs movement is calculated on?

All movements are relative to the Coordinate System instead of relative to the end point of the previous move (G91). Use (G92 X0 Y0 Z0) for movement relative to a temporary zero start position.

Units per Minute Mode. In units per minute feed mode, an F word is interpreted to mean the controlled point should move at a certain number of inches per minute, millimeters per minute, or degrees per minute, depending upon what length units are being used and which axis or axes are moving.

Related to Cycle Start which is set to Auto by default for grbl. This state essentially has no effect unless disabling auto start mode.

M3 will start the Spindle unless (S0). Set Spindle speed up to S12000 to turn the spindle on.

Not important because the spindle used on the ZTW is air cooled when in operation.

I didn't look too deeply into using MakerCAM because of some of its limitations.

By default MakerCam seems to add the following to the beginning of the G-code File:

G21 G92 G40

• G21 millimeters
• G90 Absolute Machine Positioning
• G40 Tool radius comp off Not Supported by Grbl

GcodeTools is good to use for simple follow path engraving operations. Instructions. Copy the header/footer files from this repository into the specified output directory to automatically add the necessary gcode to use start position offset and start/stop the spindle.

MeshCam seems to be a great program for doing 3D machining operations.

By default MeshCam adds the following: G21 G91

• G21 mm
• G91 Movements relative from First fixture location

I've Used OpenSCAM to do 3D operations, but it is a commerical program that costs $250.