CNC glossary
Short definitions. Each links to the module that explains it properly.
Allowance
Material deliberately left on a surface by a roughing pass for the finishing pass to remove. Also called stock to leave. Read more
Backlash
Lost motion when an axis reverses direction, caused by slack in the drive. Shows up as circles that are not round and dimensions that differ depending on approach direction. Read more
Ball nose
An end mill with a hemispherical tip, used for 3D finishing because it blends smoothly between passes. Read more
Board foot
A unit of lumber volume: 144 cubic inches. How hardwood is priced. Read more
CAD
Computer Aided Design. Drawing the shape. Read more
CAM
Computer Aided Manufacturing. Turning the shape into toolpaths. Read more
Chipload
The thickness of material one flute removes in one revolution. The central number in feeds and speeds. Read more
Climb cutting
Cutting with the tool rotation moving in the same direction as the feed. Usually the better finish on a rigid machine. Read more
Collet
The split sleeve that grips the bit shank. Not the same thing as a chuck, and it has rules. Read more
Compression bit
A spiral with an upcut lower section and a downcut upper section, giving clean edges on both faces of plywood. Read more
Conventional cutting
Cutting against the direction of tool rotation. More forgiving on loose machines. Read more
DOC
Depth of cut. How deep a pass goes, measured along Z. Read more
Downcut
A spiral that pushes chips downward, holding the top surface fibres down for a clean top edge. Read more
Feed rate
How fast the tool travels through the material, in units per minute. Read more
Flute
A cutting edge on the bit, and the groove behind it that carries chips out. Read more
G-code
The text language of machine movements. Read more
Helix
The angle of the spiral cutting edge. Affects cutting action and chip movement. Read more
Home
A fixed physical reference position the machine finds using limit switches. Read more
Kerf
The width of material removed by a cut. For a router it equals the cutting diameter. Read more
MRR
Material removal rate. Feed times depth times width of cut. The best single measure of how hard the machine is working. Read more
Onion skin
A very thin layer of material left instead of cutting all the way through, holding parts in place. Cut or sanded off afterwards. Read more
Origin
The point your design is measured from, set on the material as work zero. Read more
Plunge rate
How fast the tool moves straight down into material. Almost always slower than the feed rate. Read more
Pocket
A toolpath that clears all the material inside a closed shape to a depth. Read more
Post processor
The translator that writes toolpaths as G-code in your controller's dialect. Read more
Profile
A toolpath that follows a shape's outline, cutting inside it, outside it, or on the line. Read more
Rest machining
A pass with a smaller tool that only cuts where the previous larger tool could not reach. Read more
Runout
How much a bit wobbles off the true axis of rotation. Causes uneven flute loading and poor finish. Read more
Scallop
The ridge left between adjacent passes of a round-nosed cutter. Read more
Spoilboard
The sacrificial surface under your work that the bit is allowed to cut into. Read more
Stepdown
How much deeper each successive pass goes. Same idea as depth per pass. Read more
Stepover
How far the tool moves sideways between passes. Read more
Stickout
How far the bit protrudes from the collet. Every extra millimetre increases deflection sharply. Read more
Surfacing
Flattening a surface with a wide flat bit, most often the spoilboard or a slab. Read more
Tab
A small uncut bridge that holds a part in the sheet until the job finishes. Read more
Tram
Squaring the spindle to the table so a flat cutter leaves a flat surface rather than an arc. Read more
Upcut
A spiral that lifts chips up and out, clearing deep cuts well but lifting the top fibres. Read more
V-carve
A toolpath that varies depth with shape width so a V-bit touches both walls, producing crisp lettering. Read more
WOC
Width of cut. How much of the bit's diameter is engaged sideways. Same idea as radial engagement. Read more
Work coordinates
Positions measured from the zero you set on your material, which is what toolpaths use. Read more
Zero
The point on your material that the machine treats as the origin of the job. Read more