Reference

CNC relief carving glossary

The words you meet when you carve a bas-relief STL on a CNC router, each in a sentence or two.

Bas-relief: A carving whose design rises only a little from a flat background, so it reads from the front like a picture with depth. Most wall panels, plaques and signs carved on a CNC router are bas-relief.
High relief: A carving whose subject stands far out from the background, with parts close to free-standing. It needs deeper stock and longer bits than bas-relief.
STL file: A 3D model saved as a mesh of triangles. CAM software, slicers and modelling programs all read it. It carries no units, so you tell the software whether it is in millimetres or inches. Opening an STL in your software →
Bas-relief STL: A bas-relief saved as an STL: a triangle surface that rises from a flat back. On a CNC router it is roughed with an end mill and finished with a ball nose.
Mesh: The surface of a 3D model made of many small triangles. More triangles hold finer detail and make a larger file.
Triangle count: How many triangles a mesh has. A detailed relief often has one to two million; CAM software that slows down on large meshes can reduce the count first.
Watertight: A mesh with no holes or gaps, so its surface fully encloses a volume. CAM software and slicers handle watertight meshes predictably.
Flat base (zero plane): The flat back of a relief, sitting at height zero. It lies on the board so the carving starts from a known level.
Relief depth: The height from the flat base to the highest point of the carving. It decides the board thickness you need and much of the carve time.
Z scaling: Changing the depth of a relief on its own. Scaling all three axes keeps the proportions; scaling only Z makes the carving shallower or deeper for your stock. Scaling without losing detail →
CAM software: Software that turns a 3D model into toolpaths and G-code for the machine. Aspire, VCarve, Carveco, ArtCAM and Fusion 360 are common for reliefs. Comparing the main programs →
Toolpath: The route a cutter follows over the material, with its speeds and depths. A relief usually takes a roughing toolpath and a finishing toolpath.
Roughing: The first pass, which clears most of the waste quickly with a flat end mill, leaving a little material above the final surface.
Finishing: The pass that cuts the final surface with a ball nose, line by line across the carving.
End mill: A cutter with a flat bottom. It clears material fast and is used for roughing and for cutting the outline.
Ball nose: A cutter with a rounded tip. It follows a curved surface, so it is the bit that carves relief detail. Its radius sets the finest detail it can reach. 3 mm vs 1.5 mm, measured →
Tapered ball nose: A ball nose whose body widens above a small rounded tip. The thin tip reaches fine detail while the thicker body keeps it from snapping. Choosing a tapered ball nose →
Raster: A finishing pattern of parallel straight passes across the carving, like lines of text. It is the most common finishing strategy for reliefs.
Stepover: How far the cutter moves sideways between passes, often given as a percentage of its diameter. Smaller stepover means smaller ridges and a longer job. Stepover calculator →
Scallop: The small ridge a ball nose leaves between two passes. Its height is r − √(r² − (s/2)²), where r is the ball radius and s the stepover; with a 1/8 inch ball at 10 percent it is under 0.01 mm.
Stepdown (depth of cut): How deep the cutter goes in one roughing pass. Deep reliefs are roughed in several stepdowns, which is what leaves the terraces a finishing pass removes.
Rest machining: A pass with a smaller bit that cuts only where a bigger bit could not reach, instead of going over the whole carving again. It brings out fine detail in a fraction of the time. How much time rest machining saves →
Machining boundary: A closed vector that limits a toolpath to the area inside it, so the machine cuts the carving and leaves the rest of the board alone. Make a boundary from an STL →
Greyscale depth map: An image in which darker means deeper. Laser engravers work from such images rather than from an STL, so a relief is converted to one before burning. STL files for laser engraving →

More questions answered in the FAQ, or browse the carving guides.