4-Axis Mill

Configuration for a 4-axis CNC mill with rotary axis. Ideal for machining complex parts that require rotation around a cylindrical workpiece.

Machine Specifications

This recipe is designed for:

• 4 stepper motors (X, Y, Z linear + A rotary)
• Homing on linear axes (X, Y, Z)
• Rotary axis without homing (A-axis)
• Spindle with speed control
• Standard ESP32 board

Complete Configuration

name: "4-Axis Mill"
board: "ESP32"
version: "3.7"

axes:
  x:
    steps_per_mm: 80.0
    max_rate_mm_per_min: 4000.0
    acceleration_mm_per_sec2: 400.0
    max_travel_mm: 200.0
    soft_limits: true
    homing:
      cycle: 1
      positive_direction: false
      mpos_mm: 0.0
      feed_mm_per_min: 1000.0
      seek_mm_per_min: 2000.0
    motor0:
      step_pin: "gpio.2"
      direction_pin: "gpio.5"
      disable_pin: "gpio.8"
    limit_neg_pin: "gpio.9"

  y:
    steps_per_mm: 80.0
    max_rate_mm_per_min: 4000.0
    acceleration_mm_per_sec2: 400.0
    max_travel_mm: 150.0
    soft_limits: true
    homing:
      cycle: 1
      positive_direction: false
      mpos_mm: 0.0
      feed_mm_per_min: 1000.0
      seek_mm_per_min: 2000.0
    motor0:
      step_pin: "gpio.3"
      direction_pin: "gpio.6"
      disable_pin: "gpio.8"
    limit_neg_pin: "gpio.10"

  z:
    steps_per_mm: 400.0
    max_rate_mm_per_min: 1500.0
    acceleration_mm_per_sec2: 150.0
    max_travel_mm: 100.0
    soft_limits: true
    homing:
      cycle: 2
      positive_direction: true
      mpos_mm: 100.0
      feed_mm_per_min: 500.0
      seek_mm_per_min: 1000.0
    motor0:
      step_pin: "gpio.4"
      direction_pin: "gpio.7"
      disable_pin: "gpio.8"
    limit_pos_pin: "gpio.11"

  a:
    steps_per_mm: 8.888889  # 360°/40.5 = 8.888889 steps per degree
    max_rate_mm_per_min: 3600.0  # 360°/min = 6 RPM
    acceleration_mm_per_sec2: 600.0
    max_travel_mm: 360000.0  # Effectively unlimited rotation
    soft_limits: false  # No soft limits for rotary
    motor0:
      step_pin: "gpio.25"
      direction_pin: "gpio.26"
      disable_pin: "gpio.8"
    # No homing switch for rotary axis

spindle:
  pwm:
    pwm_hz: 5000
    output_pin: "gpio.12"
    enable_pin: "gpio.13"
    direction_pin: "gpio.14"
    spinup_ms: 2000
    spindown_ms: 2000
    tool_num: 0
    speed_map: "0=0% 1000=10% 18000=100%"

probe:
  pin: "gpio.15"
  check_mode_start: true

control:
  safety_door_pin: "gpio.16"
  reset_pin: "gpio.17"
  feed_hold_pin: "gpio.18"

coolant:
  flood_pin: "gpio.19"

Pin Assignment Summary

Function	GPIO Pin	Notes
X Step	2	X-axis linear movement
Y Step	3	Y-axis linear movement
Z Step	4	Z-axis linear movement
A Step	25	A-axis rotary movement
X Direction	5	X-axis direction control
Y Direction	6	Y-axis direction control
Z Direction	7	Z-axis direction control
A Direction	26	A-axis direction control
Motor Enable	8	Shared enable for all motors
X Limit	9	X-axis homing switch
Y Limit	10	Y-axis homing switch
Z Limit	11	Z-axis homing switch
Spindle PWM	12	Spindle speed control
Spindle Enable	13	Spindle on/off
Spindle Direction	14	CW/CCW rotation
Probe	15	Touch probe input
Safety Door	16	Emergency stop
Reset	17	Reset button
Feed Hold	18	Feed hold button
Coolant	19	Coolant pump

Rotary Axis Configuration

Steps per Degree Calculation

For rotary axis, steps_per_mm represents steps per degree:

steps_per_degree = (motor_steps × microsteps × gear_ratio) / 360°

Example with 1.8° stepper, 16 microsteps, 40:1 gearbox:
steps_per_degree = (200 × 16 × 40) / 360 = 8.888889

Speed Settings

Rotary axis speeds are in degrees per minute:

• max_rate_mm_per_min: 3600 = 360°/min = 6 RPM
• acceleration_mm_per_sec2: 600 = 600°/sec² acceleration

No Homing for Rotary

Rotary axes typically don't home:

• No limit switches on A-axis
• No homing cycle configured
• Soft limits disabled for continuous rotation

Customization Guide

Linear Axes Adjustment

Same as 3-axis machines:

• Adjust steps_per_mm for your mechanical setup
• Set travel limits to match your machine
• Tune speeds for your motors and drivers

Rotary Axis Tuning

Gear Ratio Calculation

Most rotary axes use reduction gearing:

# For different gear ratios:
# 10:1 ratio: steps_per_mm: 2.222222
# 20:1 ratio: steps_per_mm: 4.444444  
# 50:1 ratio: steps_per_mm: 11.111111
# 90:1 ratio: steps_per_mm: 20.0

Speed Considerations

Rotary axes are usually slower:

• Conservative speeds prevent workpiece damage
• Lower acceleration for heavy workpieces
• Consider workpiece inertia when setting limits

Spindle for Milling

Configured for variable speed milling:

spindle:
  pwm:
    speed_map: "0=0% 1000=10% 18000=100%"  # Typical mill speeds
    spinup_ms: 2000   # Longer spinup for heavy spindles
    spindown_ms: 2000 # Longer spindown for safety

4-Axis G-code Usage

Basic 4-Axis Commands

G90           ; Absolute positioning
G0 X10 Y10 Z5 A45  ; Position all 4 axes
G1 X20 A90 F500    ; Simultaneous linear and rotary move
A360          ; Full rotation (360 degrees)

Typical 4-Axis Operations

Cylinder Machining

; Machine around cylinder circumference
G0 Z10 A0     ; Start position
G1 Z0 F200    ; Plunge to depth
G1 A360 F300  ; Machine full rotation
G0 Z10        ; Retract

Helical Milling

; Helical thread cutting
G0 X0 Y0 Z10 A0   ; Start position
G1 Z0 F100        ; Plunge start
G1 X0 Y0 Z-10 A360 F200  ; Helical move

Index Operations

; Machine multiple features around circumference
G0 A0         ; Index to 0°
; ... machining operations ...
G0 A90        ; Index to 90°
; ... machining operations ...
G0 A180       ; Index to 180°
; ... machining operations ...

Workholding Considerations

Chuck vs. Centers

• Chuck holding: Good for short, rigid parts
• Between centers: Better for long, slender parts
• Tailstock support: Reduces deflection and chatter

Workpiece Balance

• Dynamic balancing important at higher speeds
• Counterweights may be needed for irregular shapes
• Speed limitations based on workpiece geometry

Safety Considerations

Rotary Axis Safety

• No soft limits means potential for wrap-around
• Manual positioning before starting programs
• Chuck/workpiece clearance critical
• Emergency stop easily accessible

Tool Clearance

• Longer tools may be needed for deep features
• Tool path planning must consider rotary motion
• Collision detection more complex with 4 axes

Troubleshooting 4-Axis Issues

A-Axis Not Moving

1. Check motor connections and driver settings
2. Verify step/direction pin assignments
3. Test with manual commands (G1 A10)
4. Check gear backlash and mechanical binding

Positioning Accuracy

1. Calibrate steps per degree with test cuts
2. Check gear backlash compensation
3. Verify motor torque adequate for workpiece
4. Test repeatability with index positioning

Synchronization Issues

1. Tune acceleration for all axes
2. Balance speeds between linear and rotary
3. Check mechanical rigidity of rotary axis
4. Verify timing in multi-axis moves

Advanced Features

Tool Length Compensation

G43 H1        ; Tool length offset
G0 Z10 A45    ; Position with offset active

Coordinate System Rotation

Some CAM software supports:

• G68: Coordinate system rotation
• Compound angles with A-axis positioning
• 3D surface machining on cylinders

Maintenance

Regular Checks

• Rotary axis backlash measurement
• Chuck/collet condition
• Gear lubrication as needed
• Encoder feedback (if equipped)

Calibration

• Periodic steps/degree verification
• Index repeatability testing
• Runout measurement of workholding
• Tool setter calibration for 4-axis

Next Steps

• Custom Board Setup - Advanced board configurations
• Expert Editor - Fine-tune advanced settings
• Pin Mapper - Manage complex pin layouts

4-axis machining opens up new possibilities for complex part manufacturing. Take time to understand the rotary axis behavior before attempting complex programs! 🔄