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Vector and Raster Modes in Laser Engraving

In raster engraving, the laser traces a slowly advancing pattern across the surface in a back-and-forth motion like an inkjet printer.

In vector engraving, the line and curve of the pattern to be engraved are followed much like a pen-based plotter draws lines from a pattern outline. Early engraving, laser and traditional, of signs and plaques often used prestored font outlines to scale and reproduce letters, numbers, and even logos to size with precise strokes. Unfortunately, due to a lack of precision in calculating spacing's, “fill” areas, as cross-hatching patterns and dot-fills, sometimes showed moiré effects or uber-patterns. Moreover, the font device was not capable of rotations or dynamic scaling. Today the PostScript software language allows much greater flexibility. Just about anything that can be described in vectors by software using PostScript, such as Corel Draw or Adobe Illustrator, can be outlined, filled in with appropriate patterns, and laser engraved.

In raster engraving, the laser traces a slowly advancing pattern across the surface in a back-and-forth motion like an inkjet printer. Areas to either side of the pattern to be engraved are ignored, thus shortening the trace for better efficiency. The advance of each line normally takes less time than the actual dot-size of the laser; the engraved lines overlap slightly to create continuity.

In all raster engravings, curves and diagonals will suffer if the length or position of the raster lines vary even slightly in relation to the raster scan. Therefore, exact positioning and repeatability are critical in the machine’s design. Raster engraving produces a nearly effortless fill. Most images to be engraved in raster mode consist of bold letters or have large engraved areas. These can be well rasterized. Rasterized photos, as in printing, have dots larger than that of the laser's spot. These are also best engraved as a raster image.

Almost any layout software can feed a raster driver for an X-Y or drum laser engraver. Traditional plaque and sign engraving had to use the solid strokes of vector mode engraving, but modern shops run their laser engravers mostly in raster mode. They reserve vector mode for achieving the traditional outline look or for quickly marking out lines or hatches where a plate is to be cut.

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