CNC G-Code Simulator

The CNC G-Code Simulator is an interactive tool for writing, visualizing, and animating CNC programs. G-code is the standard programming language that controls Computer Numerical Control machines, instructing them where to move, how fast to cut, and what operations to perform. This simulator lets you write G-code in a syntax-highlighted editor and instantly see the resulting tool path rendered on a virtual workpiece in 2D or 3D isometric view.

The simulator supports all fundamental motion commands: G00 (rapid positioning), G01 (linear interpolation at controlled feed rate), G02 (clockwise circular arc), and G03 (counter-clockwise circular arc). It also recognizes coordinate modes (G90 absolute, G91 incremental), unit selection (G20 inch, G21 metric), and M-codes for spindle and program control. 17 example programs are included, ranging from basic squares to bolt hole circles, face milling patterns, contour chamfers, 5-pointed stars, circular pockets, and multi-pass depth programs with Z-axis colour visualization.

The simulator opens in Simulate mode with a split layout: the syntax-highlighted G-code editor on the left and the tool path canvas on the right. The Control Panel toolbar provides an example program selector (17 programs), Run, Step, Reset, Clear, 3D view toggle, animated Tool toggle, Arrows toggle, MM/IN units toggle, and a Cheat Sheet button. Below the canvas, a speed slider controls animation playback rate. The readout row shows current X/Y coordinates, feed rate, spindle RPM, program line, and total path length. A yellow-blinking guide highlights the next action button.

To run your first program: (1) Select an example from the dropdown (e.g., Square Profile). The editor fills with syntax-highlighted G-code. (2) Click "Run" to animate the tool path from start to finish. Watch the tool move on the canvas, with rapid moves as dashed lines and cutting moves as solid coloured lines. (3) Use "Step" to execute one line at a time, watching the current line highlight in the editor and the tool advance on the canvas. (4) After completion, a Toolpath Statistics panel shows cut distance, rapid distance, total moves, estimated cut time, and bounding box. (5) Click "Reset" to return to the start, or "Clear" to empty the editor and write your own code. Hover over the canvas to see real-time X/Y machine coordinates.

The editor features full syntax highlighting: G-codes appear in green, M-codes in orange, coordinates (X/Y/Z/I/J/R/Q) in blue, S/F/T values in purple, and comments in gray. A line indicator shows which line is currently executing, with a yellow highlight bar on the active line. The canvas renders the complete tool path with distinct colours: rapid moves (G00) as dashed gray, linear cuts (G01) in green, clockwise arcs (G02) in blue, counter-clockwise arcs (G03) in red, and drill holes (G81/G83) as purple circles with crosshairs.

Canned Cycles (G81/G83/G73/G84): Type a drilling canned cycle to visualise hole patterns. G81 drills at each X/Y position; G83 peck-drills in increments (Q value). Once a canned cycle is active, each subsequent line with only X/Y coordinates repeats the drill at that new position. Use G80 to cancel. The Toolpath Statistics panel counts drill holes separately.

Tool Diameter (⌀ mm): Enter a tool diameter in the speed row to show a translucent cut-width band along every cutting move. This helps visualise material removal width at a glance. Set to 0 to hide. Keyboard shortcuts: F5 = Run/Pause, F8 = Reset, F10 = Step.

3D View: Toggle the 3D button to see your tool path in an isometric perspective. Animated Tool: Toggle the Tool button to see a spinning disc with cutting flutes and a feed direction arrow. Use Ctrl+Scroll to zoom, drag to pan, or use the +/−/reset buttons. The Cheat Sheet button opens a quick-reference overlay with all G-codes, M-codes, canned cycles, and parameters.

Click the Explore tab to access a reference library organized into three categories: G-Codes, M-Codes, and Programming Concepts. Each category presents a grid of selectable concept cards. Click any card to view a detailed explanation with syntax examples and visual tool path illustrations.

G-Code topics cover G00 (rapid), G01 (linear cut), G02/G03 (arcs with I/J center offsets), G90/G91 (absolute/incremental), G20/G21 (units), and G28 (home return). M-Code topics explain M03/M04/M05 (spindle), M08/M09 (coolant), M00 (program stop), and M30 (program end). Programming concepts cover program structure, block format, coordinate systems, cutter compensation, and tool change sequences. This is your quick-reference guide for G-code syntax.

Practice mode tests your G-code knowledge with exercises. You might be asked to identify the correct G-code for a specific motion, determine the endpoint of an arc command, or write the coordinates to produce a given tool path. Enter your answer and check it. Solutions explain the reasoning behind each answer.

Quiz mode presents five questions per session covering G-code commands, M-codes, arc programming, coordinate systems, and program structure. Questions range from basic identification (what does G02 do?) to practical application (write the command to cut a clockwise semicircle). Review your score and retake to master CNC programming fundamentals.

• Start with the Square Profile example to understand basic G00 and G01 commands, then progress to Circle, Oblong Slot, and Complex Contour for arc programming. Try advanced examples like Bolt Hole Circle (G02 arcs in a pattern) and Circular Pocket (concentric cuts).
• Use Step mode to execute one line at a time, watching how each command moves the tool. This is the best way to learn arc commands (G02/G03). The editor highlights the active line.
• For arc commands, remember: I and J are the offsets from the current position to the arc center, not the absolute center coordinates. Open the Cheat Sheet for a quick-reference table.
• Always start programs with a safety line: G90 G21 G17 (absolute, metric, XY plane), then M03 S3000 (spindle on), and end with M05 M30 (spindle off, program end).
• Enable the 3D view to better understand spatial relationships in your tool path. Enable the Tool toggle to see spindle rotation and feed direction during animation.
• Hover over the canvas to see real-time X/Y machine coordinates. Use Ctrl+Scroll to zoom in on details, and drag to pan around.
• After running a program, check the Toolpath Statistics panel for cut distance, rapid distance, estimated machining time, and bounding box dimensions.
• Try writing your own programs after studying the examples. Start simple (a triangle or rectangle) and add arcs as you gain confidence. Use the syntax highlighting colours to verify your code structure.

Keyboard Shortcuts: F5 = Run/Pause, F8 = Reset, F10 = Step one line. These work whenever the editor or canvas is in focus.

Export G-Code: Click the G-Code button to download the editor content as a .nc file. Export CSV: Click CSV for a spreadsheet-ready tool path file including arc center/radius data and drill hole depths. Export PNG: Click PNG to save the canvas as an image with a watermark.

Right-click Menu: Right-click on the canvas for quick access to Save PNG, Export CSV, Export G-Code, or Reset. Fullscreen Mode: Click the yellow fullscreen button (bottom-right of canvas) to enter an immersive workspace. Press Escape or click the close button to exit.

Z-Depth Colour Visualization: When programs use negative Z values (actual cutting depth), tool path colours shift from green (Z=0, surface) to blue (deepest Z). Each pass is a different shade, making multi-pass depth cuts immediately visible. Try the "Depth Passes (Z Color)" example. The Current Z readout shows the active cutting depth.

Cut Direction Arrows (↗ Arrows): Toggle the Arrows button to overlay small directional arrows at the midpoint of every cutting move. This clearly shows the direction of travel along each segment and arc — essential for understanding climb vs conventional milling and verifying circular arc direction (G02/G03).

Toolpath Scrubber: After running a program, a range slider appears below the canvas. Drag it to scrub back and forth through the tool path at any step. The canvas updates in real time showing the tool path up to that point, and the readouts reflect the machine state at that exact moment. This is ideal for inspecting exactly where a problem occurs in a complex program.

Save/Load Slots: Three numbered slots below the editor let you save G-code programs to browser storage. Click an empty slot to save the current editor content. On a filled slot (shown with a green border), click to load it back into the editor, or Shift+click to overwrite it. Your saved programs persist between sessions.

MM / IN Toggle: Click the MM/IN button in the toolbar to switch all position and feed readouts between millimetres and inches. The canvas grid always shows native G-code units, but the X/Y/Z/Feed readout cards convert to your preferred display unit. This does not affect the machine simulation — only the displayed values change.

Speeds & Feeds Calculator (⚡ S&F Calc): Opens a calculator overlay with 9 material/tool-type presets. Select a material, enter tool diameter and flute count to get recommended spindle speed (RPM), feed rate, chip load, and surface speed. Click "Apply to Editor" to automatically insert an M03 S___ line and a recommended feed rate comment at the top of your program.

Warnings: The linter checks for: arc radius mismatch (I/J error), G01 with F=0 (stall warning), cutting moves before M03/M04 spindle start, and missing X/Y/Z coordinates. Warnings appear in a red bar with clickable line-jump buttons (Ln) to scroll the editor directly to the offending line.

Editor Line Numbers: A line number gutter on the left side of the editor shows line numbers that stay in sync as you scroll. This makes it easy to cross-reference warnings, error messages, and the program line readout.

Toolpath Statistics: After running a program, a statistics panel shows cut distance, rapid distance, moves, estimated machining time, bounding box, and drill hole count (when canned cycles are used).

Sound Feedback: Audio cues confirm button presses, program completion (ascending chime), and correct/incorrect answers in Practice and Quiz modes.