CNC G01
Linear Interpolation
A practical engineering guide to feed-controlled linear motion, CNC programming, feedrate selection, positioning modes, toolpaths and shop-floor troubleshooting.
Understand not only what G01 does, but how it interacts with WCS, tooling, workholding, cutting conditions, tolerances and inspection.
Commands controlled linear interpolation toward the programmed coordinates at the active feedrate.
Quick Engineering Answer
G01 is the CNC command used for feed-controlled linear interpolation. The control coordinates the commanded axes so that the tool follows a straight path between the current position and the programmed destination.
What Is CNC G01 Linear Interpolation?
G01 is one of the fundamental motion commands used in CNC machining. It commands the machine to perform controlled linear movement between programmed positions.
On a milling machine, the movement may involve X, Y, Z or combinations of these axes. When multiple axes move together, the CNC control coordinates their motion to produce the commanded linear path.
Conceptual G01 Linear Path
The CNC control coordinates the axes to generate the commanded linear path.
How G01 Linear Interpolation Works
Consider a tool currently positioned at:
The program then commands:
The intended endpoint is X100 Y50. The control calculates coordinated X and Y axis movement so that the tool travels along the straight line connecting the two positions.
The important engineering distinction
The programmer defines the destination and machining intent. The CNC control performs the interpolation required to coordinate the machine axes.
G00 vs G01: What Is the Difference?
G00 and G01 are both motion commands, but they have fundamentally different purposes in a CNC program.
G00 — Rapid Positioning
Typically used to reposition the machine rapidly through a verified safe region.
- Rapid positioning
- Normally non-cutting movement
- Clearance and collision control are critical
G01 — Linear Interpolation
Used for controlled linear movement at the programmed feedrate.
- Feed-controlled motion
- Commonly used for cutting
- Cutting conditions affect the result
G01 CNC Programming Syntax
A simplified milling syntax is:
| Address | Function | Engineering Significance |
|---|---|---|
| G01 | Linear interpolation | Defines the motion type. |
| X | X destination | Defines the programmed X position. |
| Y | Y destination | Defines the programmed Y position. |
| Z | Z destination | Defines the programmed Z position. |
| F | Feedrate | Defines the programmed feed movement. |
G01 with G90 and G91
Understanding G01 requires understanding how the CNC control interprets the programmed coordinates.
G90
The coordinate is interpreted as an absolute programmed destination within the active coordinate system.
G91
The coordinate represents incremental movement from the current programmed position.
See the related CNC Work Coordinate System guide and G54/G55 Work Offset guide .
Feedrate in G01
The F address specifies the programmed feedrate according to the active control and feed mode.
Feedrate is not simply a movement-speed parameter. During cutting, it directly influences cutting load, chip formation, surface finish, tool life and cycle time.
F = feedrate, mm/min
fz = feed per tooth, mm/tooth
z = effective number of teeth
N = spindle speed, rpm
Worked Example
Assume:
- Feed per tooth = 0.05 mm/tooth
- Effective teeth = 4
- Spindle speed = 3000 rpm
G01 and the CNC Work Coordinate System
G01 does not determine where the physical part is located. The active work coordinate system establishes the relationship between programmed coordinates and the actual workpiece.
Datums
Workholding
G54 / G55
Toolpath
Verify feature
A correct G01 coordinate combined with an incorrect work offset can still produce an incorrectly machined part.
Related references: CNC Datum Selection and CNC Part Zero .
G01 as Part of a Machining Strategy
A G01 block should not be considered independently from the manufacturing process. The final result depends on how the motion command interacts with tooling, workholding, machine rigidity and the machining sequence.
See Manufyn’s CNC Machining Sequence Planning guide for a deeper treatment of operation sequencing.
Tooling, Deflection and G01 Accuracy
A mathematically correct G01 path does not guarantee that the cutter physically follows the intended path under load.
Tool diameter, stickout, holder rigidity, cutting engagement and workpiece support all influence the actual machining result.
| Condition | Potential Effect | Engineering Response |
|---|---|---|
| Long tool overhang | Greater deflection and vibration risk | Reduce stickout where possible. |
| Heavy radial engagement | Higher cutting force | Review engagement and cutting strategy. |
| Thin wall | Part movement or wall deflection | Improve support and machining sequence. |
| Worn tool | Dimensional drift and surface deterioration | Establish appropriate tool-life control. |
| Weak workholding | Part movement during G01 cutting | Review fixture and clamping strategy. |
Related: CNC Tool Deflection and CNC Chatter .
G01 and Surface Finish
G01 itself does not determine surface finish. Surface quality is a result of the complete cutting system.
- Tool geometry
- Feedrate
- Spindle speed
- Tool runout
- Tool deflection
- Machine rigidity
- Workholding
- Material
- Toolpath direction
- Tool condition
See: Poor CNC Surface Finish: Causes, Diagnosis & Solutions .
Inspection of G01-Machined Features
Inspection should be selected from the drawing requirement, not from the CNC command being used.
| Requirement | Possible Inspection Method | Why |
|---|---|---|
| General linear dimension | Vernier caliper | Suitable where tolerance and feature accessibility permit. |
| Precision external dimension | Micrometer | Provides better resolution and contact control. |
| Profile/location requirement | CMM or suitable comparative method | Depends on GD&T and datum structure. |
| Surface finish | Surface roughness instrument | Quantifies the specified surface requirement. |
Related: CNC Inspection Guide and CNC Micrometer Inspection .
CNC G01 Troubleshooting Guide
When a G01-machined feature is incorrect, diagnose the complete process instead of immediately editing the coordinate.
Practical CNC G01 Example
Consider a rectangular aluminum component requiring an external profile. A simplified conceptual sequence could be:
What should be verified before running it?
- Is the correct work offset active?
- Is the program in the intended G90/G91 mode?
- Is the tool correctly measured?
- Is the toolpath clear of fixtures?
- Is the cutter compensation correct?
- Are cutting parameters appropriate?
- Has the complete tool assembly been simulated?
- How will the finished profile be inspected?
G01 and CNC Production Cost
G01 does not have a standalone “cost.” Its production impact comes from the machining strategy built around the linear movements.
| Factor | How G01 Strategy Can Affect It |
|---|---|
| Cycle time | Feedrate and toolpath length influence cutting time. |
| Tool life | Cutting load and engagement influence wear. |
| Surface finish | Poor cutting conditions can create additional finishing work. |
| Scrap | Incorrect WCS, offsets or process conditions can create rejected parts. |
| Inspection | Unstable processes may require increased inspection effort. |
| Lead time | Additional proving, rework or secondary operations increase total lead time. |
For broader costing considerations, see How to Reduce CNC Machining Cost and CNC Machining Time Calculation .
G01 Shop-Floor Checklist
Use this checklist before proving a new G01 program or changing a production toolpath.
Before Running the Program
- Drawing revision verified
- Material and stock verified
- Drawing datums understood
- Part orientation verified
- Workholding checked
- G54/G55 or applicable WCS verified
- G90/G91 verified
- Tool number verified
- Tool diameter verified
- Tool length verified
- Tool stickout checked
- Cutter compensation checked where applicable
- Feedrate reviewed
- Spindle speed reviewed
- Coolant strategy checked
- Toolpath simulated
- Fixture and holder clearance verified
- Safe approach verified
First-Off Inspection
- WCS position confirmed
- Tool approach confirmed
- Cutting load observed
- Critical dimensions inspected
- Surface finish checked
- Burrs checked
- Tool condition checked
Production Control
- Tool wear monitored
- Dimensional drift monitored
- Tool-life limits controlled
- Offset changes documented
- Critical dimensions inspected at defined intervals
Continue Learning: CNC Knowledge Hub
G01 is only one part of CNC programming. These resources connect motion commands with drawing interpretation, setup planning, workholding, tooling, inspection and production machining.
CNC G00 Rapid Positioning
Understand rapid positioning, clearance and safe movement before comparing it with G01.
Read Guide →CNC Work Coordinate System
Understand WCS, G54, part zero, datums and the relationship between drawing and machine.
Read Guide →How to Optimize CNC Toolpaths
Explore tool engagement, air cutting, transitions and cycle-time reduction.
Read Guide →High-Precision CNC Design Rules
Connect programmed geometry with practical manufacturing constraints.
Read Guide →CNC Tool Deflection
Understand why the actual cutting result can differ from the programmed toolpath.
Read Guide →CNC Inspection
Select practical inspection methods based on tolerance, feature and drawing requirements.
Read Guide →From CNC Programming to Real Manufacturing
24 Hour CNC Turning Prototype Delivered to the USA
A practical example of how CNC manufacturing, process planning and delivery requirements come together in a real project.
Read the Case Study →Design for Manufacturability: Practical Guide
Connect drawing decisions, tolerances, features and machining strategy before the CNC program reaches the machine.
Read the DFM Guide →CNC G01 Frequently Asked Questions
What is G01 in CNC machining?
What is the difference between G00 and G01?
What does F mean in G01?
Does G01 always cut material?
Does G01 move in a straight line?
What happens if G90 and G91 are confused?
Can G01 be used for facing?
Can G01 machine a circular path?
Why can a G01-machined dimension be incorrect?
Does increasing G01 feedrate always reduce cost?
Have a CNC Drawing You Want to Review?
If you’re unsure about the machining sequence, datum strategy, tool access, tolerance or manufacturability of a CNC component, Manufyn can review the drawing from a manufacturing perspective.