Glossary & Source Guide
Key CNC terms defined, plus recommended sources for going deeper. This page links terminology to the detailed lessons.
Concept
Quick definitions of common CNC terms. For full explanations, follow links to the relevant lesson.
Why It Matters
CNC has its own vocabulary. Knowing the correct terms helps you read manuals, ask questions, and communicate with machinists.
How It Works
Glossary
| Term | Meaning |
|---|---|
| Absolute (G90) | Coordinates measured from work zero |
| ATC | Automatic Tool Changer |
| Canned cycle | Preprogrammed motion sequence (G81 etc.) |
| Chuck | Workholding on a lathe |
| Climb milling | Tool rotates same direction as feed |
| Coolant | Cutting fluid (M08 on, M09 off) |
| CSS | Constant Surface Speed (G96) |
| Datum | Reference point for dimensions |
| Feed | Cutting speed of tool relative to work |
| G54 | Work coordinate system offset |
| Machine zero | Fixed home position of the machine |
| Modal | Code stays active until changed |
| NC file | G-code program text file |
| Rapid (G00) | Maximum-speed positioning move |
| RPM | Spindle revolutions per minute |
| Spindle | Rotating tool holder (mill) or work holder (lathe) |
| Turret | Rotating tool holder on a lathe |
| Work offset | Shift from machine zero to part origin |
| Backlash | Lost motion in a ballscrew direction reversal |
| Chip load | Thickness of material removed per tooth |
| Contour | Profile being machined |
| Fixture | Workholding device that locates and clamps the part |
| G-code | Geometric programming code (motion) |
| Haas | Common CNC controller brand |
| Insert | Indexable cutting tip on a tool holder |
| Jig | Workholding that guides the tool |
| Knee mill | Manual-style vertical mill with adjustable knee |
| Lathe | Machine that rotates the workpiece (turning) |
| MRR | Material Removal Rate (mm³/min) |
| Nose radius | Radius on a lathe insert tip |
| Offsets | Tool length and work coordinate corrections |
| Pitch | Distance between thread crests |
| Quill | Z-axis spindle slide on a drill press or mill |
| Runout | <>Undesired wobble of spindle or tool|
| Spindle speed | RPM of the rotating axis |
| Toolpath | Sequence of cutter positions |
| VMC | Vertical Machining Center |
| Workholding | How the part is clamped (vise, chuck, fixture) |
Recommended Sources
- Haas Automation CNC Programming Manual — free download, covers G/M codes for Haas controls.
- Society of Manufacturing Engineers (SME) — textbooks on machining fundamentals.
- Tooling catalogs — Sandvik Coromant, Kennametal, Iscar: cutting speed and feed data.
- CNC Cookbook (by Peter Smid) — comprehensive G-code reference.
- Machinery's Handbook — the standard engineering reference shop floor book.
Example
When you encounter a new term, look it up here first, then follow the link to the detailed lesson.
Common Mistakes
- Confusing similar terms — "feed per tooth" vs "feed per revolution" are different. Use the glossary.
Practice
1. What does G54 do?
Ans
Sets the work coordinate system offset.
2. Modal means?
Ans
The code stays active until another code in the same group replaces it.
3. What is ATC?
Ans
Automatic Tool Changer — the magazine that swaps tools on a mill.