How Numberwright Laser calculates

Energy per area and per length

Laser energy transfer depends on power, speed, spot coverage, and passes. The settings converter uses the standard laser energy model:

• Raster engraving (areal energy):E = P × (p / 100) / (v × d) × passes [J/mm²]where P is rated optical power in watts, p is power percentage (1–100 %), v is travel speed in mm/s, and d is line interval in mm.
• Vector cutting or scoring (linear energy):E = P × (p / 100) / v × passes [J/mm]
• Converting between machines: To achieve equivalent energy density (E) on a new laser, solve for target speed:v = P_to × (p_to / 100) / (E × d_to) × passes_toor solve for target power percentage:p = 100 × E × v_to × d_to / (P_to × passes_to)

Note: Spot size differences and wavelength differences (such as 450 nm blue diode vs 10600 nm CO2) absorb differently in various materials; always verify converted values with a test burn.

Test card order and G-code

The test card generator creates a grid of power (columns) and speed (rows) steps using GRBL 1.1 standard dialect:

• GRBL laser commands: The header sets metric units (G21), relative positioning (G91), and enables dynamic laser mode (M4 S0) or constant laser mode (M3 S0).
• S value scaling: GRBL scales laser power linearly between 0 and the controller's maximum spindle speed setting ($30):S = round(power% / 100 × $30)
• Safety run order: Cells are sorted and executed in order of ascending energy proxy (power / speed). As in LightBurn material tests, the highest-speed, lowest-power squares burn first so you can abort the job early if a cell starts to burn through.
• Rapid traverse safety: Movement between cells uses rapid travel (G0). In GRBL laser mode ($32=1), G0 automatically disables laser emission, preventing burn streaks across cell gaps.

Line interval and DPI

In laser engraving, line interval defines the center-to-center distance between adjacent scan passes in millimetres.

• Conversion formula: LightBurn defines DPI as 25.4 divided by line interval:interval_mm = 25.4 / LPILPI = 25.4 / interval_mm
• Image resolution match: To avoid resampling or pixel interpolation during engraving, the image pixel dimensions should match the scan line density:pixels_needed = ceil(size_mm / 25.4 × DPI)
• Effective DPI: If an existing bitmap image is provided, its effective resolution across the engraving size is:effective_DPI = pixels / (size_mm / 25.4)

Time and price

Job duration estimates compute laser-on motion and calibrate for machine controller acceleration:

• Raster scan time:lines = ceil(height / interval)raster_time = passes × lines × (width + 2 × overscan) / speedWhen unidirectional, the non-firing return move time is added at the designated return speed.
• Vector cutting time:vector_time = passes × cut_length / speed
• Calibration factor k: Acceleration curves, corner deceleration, and non-engraving travel add overhead in real operations. The calibration factor scales raw laser-on time: total_time = (raster + vector) × k.
• Pricing formulas:Total cost = Material + Machine time + Labor + Other costsMarkup price = Total cost × (1 + markup% / 100)Margin price = Total cost / (1 - margin% / 100)