Free CNC G-Code Generator & Toolpath Creator | Drilling, Milling & Lathe

🔧 SteelSolver Engineering Tools & Guides — featuring 260+ free calculators and 60+ in-depth guides for engineers, fabricators, and metalworkers.

👉 Find the right tool or guide for your project:

📚 Explore All Engineering Hubs on SteelSolver.com

⚙ CNC G-Code Generator — Complete User Guide Free online CNC programming tool & toolpath creator for milling, drilling, lathe, plasma, router, and laser machining

This free online CNC G-Code Generator is a browser-based CAM utility and digital toolpath creator that converts your machining parameters into ready-to-run G-code programs — without expensive software, complex CAD/CAM systems, or manual scripting. Whether you are a beginner learning CNC numerical control or a professional machinist needing fast code generation for production runs, this tool covers the full workflow from geometry definition through post-processor output and file download.

The generator supports CNC mills, drill presses, lathes, plasma cutters, routers, and laser engravers, producing G-code compatible with Fanuc, Haas, GRBL, Mach3, LinuxCNC, and Siemens Sinumerik controllers. It handles drilling cycles, bolt circle patterns, pocket milling, slot cutting, facing operations, lathe turning, threading, and grooving — with a built-in feeds & speeds calculator and visual toolpath preview.

CNC G-Code Workflow: From CAD Design to Machine Motion

The diagram below illustrates the complete digital-to-physical manufacturing pipeline — from your part design through the G-code generator and post-processor to the CNC machine controller and final fabrication.

ⓘ The complete digital engineering workflow: CAD geometry → G-Code Generator → Post-Processor → .nc File → CNC Machine production

Key User Pain Points — and How This CNC G-Code Generator Solves Them

Step-by-Step User Guide — How to Use the CNC G-Code Generator

• 1
  Select Your Machining Module (Tab)

  At the top of the tool, choose the correct operation tab for your job: Drilling, Bolt Circle, Pocket, Slot, Facing, Lathe, Feeds & Speeds, or the G-Code Cheat Sheet. Each module generates a specific toolpath type optimised for that machining operation. Beginners should start with the Drilling tab, which auto-generates a working example on load.

  Do not mix up the Drilling tab (which uses canned cycles like G81/G83) with the Pocket tab (which generates zig-zag or circular toolpaths). They serve different cutting operations.
• 2
  Choose Controller and Units

  Under Machine & Controller, select your CNC machine's control dialect from the dropdown: Fanuc / Haas (standard industry syntax), GRBL (Arduino-based CNC routers), Mach3 / Mach4, LinuxCNC, or Siemens Sinumerik. Then choose Millimeters (G21) or Inches (G20). This affects all coordinate output, depth values, feed rates, and safe-Z heights throughout the generated program.

  Common mistake: Selecting the wrong units. If your machine is metric but you generate inch G-code (G20), the tool will move 25.4× too far and crash. Always confirm your machine's unit setting first.
• 3
  Select Drilling Cycle Type (Drilling Tab)

  Choose the appropriate canned cycle for your operation: G81 for standard plunge drilling, G83 for deep hole peck drilling (full retract each peck), G73 for high-speed chip-break peck (partial retract), G82 for spot drilling with a dwell pause, or G84 for rigid tapping. Use G83 for any hole deeper than 3× the tool diameter to prevent chip packing and tool breakage.

  Rule of thumb: Hole depth > 3× drill diameter = always use G83 peck drilling. Forgetting this is the most common reason for drill breakage in deep holes.
• 4
  Select Hole Pattern and Enter Coordinates

  Choose Single Hole, Linear Array, or Rectangular Grid. For a single hole, enter the X and Y coordinate. For a linear array, enter start X/Y, spacing between holes, hole count, and axis direction. For a grid, enter origin, number of rows and columns, and X/Y spacing. All coordinates are in the selected unit (mm or inch) relative to your Work Coordinate System (WCS) origin (G54 by default).

  For bolt circle / PCD patterns (flanges, pipe flanges), use the dedicated Bolt Circle tab — it automatically calculates all X/Y positions using the polar coordinate formula.
• 5
  Set Z-Axis Depth, Safe Z, and Peck Parameters

  Enter three critical Z values: Z Top (surface of the material, typically 0.000), Z Depth (final drill depth — must be a negative number, e.g. −20), and Safe Z (clearance height above the part for rapid moves, e.g. 5). For G83/G73 peck cycles, also enter the Peck Depth Q (how deep each peck goes before retracting) and optional Dwell P in seconds for G82.

  Z Depth must be negative (below the surface). A positive Z depth value means you are cutting upward into air, not into the material — a very common beginner mistake.
• 6
  Enter Tool Number, Spindle Speed, and Feed Rate

  Enter the Tool Number (T) (1–99), which sets both the tool change command and tool length offset register. Enter Spindle Speed (S) in RPM and Feed Rate (F) in mm/min or IPM. Not sure of the correct values? Switch to the Feeds & Speeds tab first — enter your tool diameter, material, and chip load to get automatic RPM and feed rate recommendations using the built-in calculator formulas.

  Feed rate of 0 will cause a syntax error in most controllers. If you do not know the feed rate, use the Feeds & Speeds tab to calculate it before returning to generate your drilling code.
• 7
  Configure Options: WCS, Retract Mode, Coolant, Line Numbers

  Select the Work Coordinate System (WCS) — G54 through G59 — matching your fixture offset on the machine. Choose G98 (return to initial Z height between holes) or G99 (return to R-plane only) retract mode. Toggle Flood Coolant (M08), Line Numbers (N-codes), Comments in parentheses, and Tool Length Compensation G43 on or off using the switch toggles.

  Use G98 when the fixture or clamps protrude above the part — it ensures the tool retracts fully above them between holes. Use G99 on flat plates for faster cycle times.
• 8
  Click Generate G-Code and Review the Output

  Click the orange Generate G-Code button. The tool validates all inputs (checks for positive Z depth, non-zero feeds, safe Z above surface), then generates the complete G-code program in the output panel. Review the Results Summary (hole count, depth, estimated cycle time, line count), examine the Coordinate Table for all X/Y/Z positions, and inspect the Toolpath Preview canvas showing the visual drill pattern.

• 9
  Copy to Clipboard or Download the .nc File

  Click 📋 Copy to send the G-code to your clipboard for pasting directly into your machine controller editor, or click ↓ Download to save a ready-to-load .nc file. The filename reflects the operation type (e.g. drilling.nc, bolt_circle.nc, pocket.nc). Most CNC controllers accept .nc, .tap, .txt, or .ngc formats — rename the extension if needed.

  Always run the program in DRY RUN or AIR CUT mode on your machine first (spindle on, no material) to verify all movements are correct before cutting actual stock.
• 10
  Use the Feeds & Speeds Calculator Tab

  Navigate to the Feeds & Speeds tab. Select your material from the pre-loaded library (Aluminum, Mild Steel, Stainless, Brass, Titanium, Plastic, Wood), choose your cutter type (End Mill, Ball Nose, Drill, Face Mill), enter tool diameter and flute count. The calculator applies the standard spindle speed and feed rate formulas automatically. Use the results as starting values in your drilling or milling code — always verify against your toolmaker's specifications.

All Formulas Used — Calculation Reference with Units

Every result produced by this CNC G-Code Generator is computed using the following standard machining formulas. These are the same calculations used in professional CAM software and CNC programming textbooks. All formula variables are defined with their units for clarity and trust.

1Spindle Speed (RPM) — S Parameter

The spindle speed formula converts the recommended cutting speed for a material/tool combination into the rotational speed (RPM) the CNC machine spindle must turn at. This value becomes the S word in the G-code (e.g. S1200 M03).

2Feed Rate (F Parameter) — mm/min or IPM

The feed rate is the speed at which the cutter moves through the material. It is derived from the spindle RPM, chip load per tooth, and number of cutter flutes. This becomes the F word in all G01, G02, G03, and canned cycle commands.

3Bolt Circle / PCD Hole Coordinates

The bolt circle (Pitch Circle Diameter) formula calculates the X and Y coordinates of each equally-spaced hole around a circle. This is the core calculation behind the Bolt Circle G-Code Generator tab and is used to produce the X and Y coordinate words for each drilling position.

4Arc Center Offsets I, J, K — Circular Interpolation

For G02 (clockwise arc) and G03 (counter-clockwise arc) commands, the controller needs to know the arc center position relative to the start point. The generator calculates I and J offsets automatically so you never have to do this complex geometry manually.

5Number of Peck Passes — G83 Deep Hole Drilling

When using the peck drilling cycle (G83), the generator calculates how many individual peck increments are needed to reach the final hole depth, then outputs the Q parameter accordingly.

6Material Removal Rate (MRR) — Pocket Tab

The Material Removal Rate measures how efficiently the cutter is removing stock, calculated from the axial depth of cut (step-down), stepover width, and feed rate. The Pocket tab displays this result in cm³/min.

7Stepover (WOC) and Z-Pass Count — Pocket & Facing

8Estimated Cycle Time Calculation

The generator estimates the drilling program cycle time using the total cutting distance divided by the feed rate, plus rapid move overhead. This is shown in the Results Summary section as Est. Time (sec).

9Threading & Tapping Formulas

Input Parameters Reference — Units, Valid Ranges, and Descriptions

Controller Compatibility — Post-Processor G-Code Dialects

This CNC G-Code generator supports multiple machine controller dialects through its built-in post-processor selector. Choose the correct controller to ensure generated syntax matches your machine's interpreter requirements for numerical control commands, arc formatting, and canned cycle parameters.

G-Code & M-Code Quick Reference — Commands Generated by This Tool

The following table covers every G-code and M-code command that this generator produces. Understanding these commands helps you verify the output, edit programs for your specific requirements, and understand the machine motion sequence.

Common Mistakes — Microcopy & Input Validation Guide

Frequently Asked Questions (FAQ) — CNC G-Code Generator

• What is a CNC G-Code Generator and what does it do? +

  A CNC G-Code Generator is a software utility — in this case a free browser-based tool — that converts machining parameters (coordinates, tool dimensions, speeds, depths, and operation type) into ready-to-run G-code programs. G-code is the standardised numerical control language that CNC machines — mills, lathes, routers, plasma cutters, laser engravers, and drill presses — use to control motor movements, spindle speed, and coolant.

  Instead of manually writing every G00, G01, and G83 command line-by-line (a process that is time-consuming and error-prone), you fill in a form with your job parameters and the generator produces the complete, validated code automatically. This is the same function that professional CAM software (Computer-Aided Manufacturing) performs, but focused on common operations that do not require full 3D CAD/CAM integration.

• Is this G-Code Generator free to use? Does it require any download or installation? +

  Yes — this is a completely free, browser-based online CNC G-Code Generator. There is no software download, no installation, no account required, and no usage limits. It runs entirely in your web browser using standard HTML, CSS, and JavaScript. You can use it on any desktop computer, laptop, or mobile device — including on the workshop floor directly from a tablet or phone.

• Which CNC controllers is the generated G-code compatible with? +

  The generator includes a post-processor selector supporting: Fanuc / Haas (the most common industrial standard), GRBL (used in Arduino-based CNC routers and engravers), Mach3 / Mach4 (common in hobby and small shop CNC mills), LinuxCNC (open-source controller using RS274 dialect), and Siemens Sinumerik 840D (European industrial machines using CYCLE-based programming).

  For GRBL machines specifically, the generator expands canned drilling cycles (G81/G83) into individual linear moves since GRBL does not natively support canned cycles. All other controllers use standard G-code syntax with minor dialect differences in header formatting and comment style.

• What is the difference between G81 and G83 drilling cycles? +

  G81 — Standard Drilling: The tool plunges to the programmed Z depth in one continuous motion at the specified feed rate, then retracts at rapid speed. Suitable for holes up to approximately 3× the drill diameter deep, where chip evacuation is not a problem.

  G83 — Peck Drilling: The tool plunges to a programmable peck depth (Q value), then fully retracts to the R-plane to clear chips from the flutes, then plunges again. This cycle repeats until the final Z depth is reached. Essential for deep holes (greater than 3–5× diameter), through-holes in difficult materials, or any situation where chip packing could break the drill.

  G73 — High-Speed Peck: Similar to G83 but only partially retracts (a small break) rather than fully retracting. Faster cycle time but less effective chip clearance. Good for shallow peck depths in aluminium.

• How does the bolt circle G-Code generator calculate hole positions? +

  The bolt circle module uses the standard polar-to-Cartesian coordinate conversion formula. Given the circle center coordinates, the Pitch Circle Diameter (PCD), the number of holes, and the start angle, each hole's X and Y position is calculated as:

  \( X_n = X_c + R\cos(\theta_0 + (n-1) \times 360°/N) \) and \( Y_n = Y_c + R\sin(\theta_0 + (n-1) \times 360°/N) \)

  Where R = PCD/2. This is the same calculation performed manually from engineering drawings. The generator does this for all N holes simultaneously and outputs the complete G-code drilling program with accurate coordinates to 4 decimal places.

• How do I calculate the correct spindle speed and feed rate for my material? +

  Use the built-in Feeds & Speeds Calculator tab. Select your material from the library (Aluminum, Steel, Stainless, Brass, Titanium, Plastic, Wood), choose your cutter type, enter the tool diameter and flute count. The calculator pre-loads recommended cutting speeds and chip loads from the material database, then applies the formulas:

  \( S = (V_c \times 1000) / (\pi \times D) \) for spindle speed and \( F = S \times f_z \times z \) for feed rate.

  The results give you recommended starting RPM and feed rate values. Copy these into your drilling or milling operation parameters. Always start at 70–80% of the calculated value on your first test cut, then increase gradually.

• What file format does the generator output and how do I load it onto my machine? +

  The generator produces standard ASCII text G-code that can be saved as .nc, .tap, .txt, or .gcode files. Click the Download button to save the file directly to your computer. To load it onto your CNC machine, use one of these methods:

  • USB/Flash Drive: Copy the .nc file to a USB stick and load via the controller's USB port (Haas, Fanuc with USB option).
  • Serial/DNC Transfer: Use DNC software to transfer the file via RS-232 serial connection to older controllers.
  • Ethernet/Network: Many modern controllers support network file transfer via FTP or proprietary software.
  • Direct Paste: For GRBL machines using software like Universal G-Code Sender (UGS), copy the code to clipboard and paste directly into the sender program.
  • SD Card: Common for Mach3/GRBL routers — save the file to an SD card.
• Can I use this tool for plasma cutting, laser engraving, and router operations? +

  Yes. The core G-code motion commands — G00 rapid positioning, G01 linear cutting, G02/G03 arc interpolation — are the same across CNC mills, routers, plasma tables, and laser engravers. The key differences are: plasma and laser machines do not use Z-axis depth cutting in the same way (they use torch height/focal distance control), and they use different M-codes for torch/laser on/off (typically M03/M05 or custom M-codes).

  For plasma and laser operations, generate the drilling or slot milling code that matches your cutting path geometry, then manually edit the Z references and add your machine's specific torch-on/torch-off commands. The generated linear and arc motion code (G00, G01, G02, G03, feed rates, and coordinates) will be directly usable.

• What is Work Coordinate System (WCS) / G54 and how do I set it up on my machine? +

  The Work Coordinate System (WCS) defines where X0, Y0, Z0 (part zero / datum) is located on your machine. G54 is the most commonly used work offset register. All coordinates in the generated G-code are relative to this zero point.

  To set G54 on your machine: (1) Physically touch-off your reference point (usually a corner or center of the workpiece) with a tool or edge finder. (2) Go to the machine's Work Offsets page. (3) Record the machine coordinates at that position into the G54 X, Y, Z registers. (4) The generator uses G54 in the program header, so all X/Y/Z moves are automatically relative to your set zero point. G55 through G59 are used for multiple fixtures or setups on the same machine table.

• How accurate is the estimated cycle time shown in the results? +

  The cycle time estimate is a simplified approximation based on total cutting distance divided by feed rate, plus a small overhead per hole for rapid moves and acceleration/deceleration. It does not account for: tool change time, spindle ramp-up time, machine acceleration/deceleration limits, or air-cut distances between separate features.

  For a 6-hole drilling program, the estimate is typically accurate to within ±20–30% of actual machine time. For production planning and quoting, multiply the estimated time by 1.3–1.5 as a safety factor. The estimate improves in accuracy as hole count increases.