Prepared from parser behavior, machining-file examples and visual checks performed in CNC Viewer. Always confirm the result against the CAM setup and machine documentation before production.
PLT interpretation
How to preview PLT CNC files with depth and thickness
PLT files are often excellent at describing two-dimensional pen movement but incomplete as machining programs. A safe solid preview must separate plotted geometry from machining assumptions supplied by the operator.
PLT describes movement, not necessarily machining intent
HPGL-style commands such as PU and PD indicate pen-up positioning and pen-down drawing. They can provide X and Y paths, but commonly contain no stock thickness, cutter diameter or Z depth. Treating every pen-down contour as a through-cut would invent information that is not present in the file.
Coordinate scale also varies. Plotter units are frequently smaller than a millimetre, and some exporters write initialization or scaling commands. The preview dimensions should be checked against a known part size before tool geometry is applied.
Ask for the three missing machining values
When the file does not define them, the viewer needs stock thickness, cut depth and cutter diameter. A default of 3 mm can provide a visible first result, but each value should remain editable and clearly marked as user supplied. Thickness limits the solid body, depth controls the vertical removal and diameter expands the centerline into a physical channel.
These values are independent. A 3 mm cutter at 3 mm depth on 18 mm stock creates a shallow 3 mm-wide groove. Changing the stock to 3 mm turns the same depth into a through-cut, while changing only the cutter to 6 mm widens the groove without making it deeper.
- Confirm coordinate units
- Set stock thickness
- Set cut depth
- Set full cutter diameter
Pen-up moves must not remove material
A pen-up move connects two drawing regions without marking the plot. In a CNC interpretation it behaves like a rapid positioning move and should remain visible only when non-cutting travel is intentionally displayed. Subtracting material along it creates diagonal scars between otherwise separate contours.
Likewise, repeated points and tiny closing moves should be normalized before rasterization. They may be harmless in a plotter but can add thousands of redundant samples to a high-density solid calculation.
Choose density after the scale is correct
High and Ultra density improve the sampling of curves and small cutters; they cannot repair a wrong coordinate scale or missing depth. First validate the overall width and height at Medium density. Then increase density only for the final edge check.
If Ultra appears identical to Medium, inspect whether the source path itself is made of coarse line segments. Surface resolution can smooth the swept cutter boundary, but it cannot reconstruct geometry that the PLT exporter never wrote.