Dot duration in laser engraving, explained

Dot duration is how long the laser stays on each dot when it engraves a bitmap, measured in microseconds. A longer duration puts more energy into each dot: darker, deeper marks and longer jobs. It is a setting you meet on machines that engrave dot by dot, such as xTool's F1 and F1 Ultra, where xTool offers it for bitmap engraving. Gantry diode and CO2 lasers have no dot duration field; they get the same effect from the speed setting.

• Dot duration = dwell time per dot, in µs
• Longer duration = more energy per dot
• Gantry lasers: set by speed instead

The two are often confused because both change how dark an engraving gets. Line density, line interval and DPI describe where the dots are — how close together they sit. Dot duration describes how long each dot is burned. Raise the line density and more dots share the same area; raise the dot duration and each dot gets more energy. Change both at once and the material can overheat quickly, which is why the DPI and the dwell time have to be matched to each other.

• Line density / DPI: where the dots are
• Dot duration: how long each dot burns
• Raising both at once overheats quickly

On a gantry laser the head moves continuously, and the time it spends on each dot follows from the dot spacing and the speed: time per dot = dot spacing ÷ speed. At 254 DPI the spacing is 0.1 mm, so at 100 mm/s each dot takes 1 ms (1,000 µs), at 250 mm/s 400 µs and at 500 mm/s 200 µs. That lets you translate a dot duration you read about into a speed on your own machine — as arithmetic, not as a recommendation, because power and the material decide the result.

• Time per dot = dot spacing ÷ speed
• 0.1 mm at 100 mm/s = 1,000 µs
• 0.1 mm at 500 mm/s = 200 µs

Vextrify drives gantry lasers — diode lasers with GRBL and CO2 lasers with Ruida controllers — so the energy per dot is set through speed, power and line interval, not a dot duration field. Galvo machines that use dot duration are not driven by Vextrify; for those it prepares the image. The reliable way to your own values is a short material test grid, which Laser Control builds as real objects on the bed, rather than copying a number from another machine.

• Gantry lasers: speed, power and line interval
• Galvo machines: file preparation, not live control
• Own values from a material test grid