rotation distance calculator klipper

Klipper, the advanced 3D printer firmware, offers unparalleled control and flexibility. One of its core parameters, rotation_distance, is crucial for accurate movement and extrusion. Unlike traditional Marlin firmware that uses steps_per_mm, Klipper's rotation_distance provides a more intuitive and often more precise way to define how much linear or rotational movement occurs per full rotation of your stepper motor.

This guide and accompanying calculator will help you understand, calculate, and calibrate your rotation_distance for various components of your Klipper-powered 3D printer, from extruders to linear axes.

What is Klipper's rotation_distance?

In Klipper, rotation_distance defines the linear distance (in millimeters) or the amount of filament extruded (in millimeters) that occurs when the stepper motor for that axis or extruder completes one full rotation. It simplifies the configuration by abstracting away microsteps and full steps per rotation from the primary movement calculation.

Instead of calculating steps_per_mm based on motor steps, microsteps, and mechanical properties, Klipper directly uses rotation_distance. The firmware then internally calculates the number of steps required to achieve a desired movement, taking into account the motor's full steps per rotation and the configured microsteps.

Why is it Important?

• Accuracy: Correct rotation_distance values ensure your printer moves and extrudes with high precision, leading to dimensionally accurate prints.
• Consistency: It provides a consistent way to define movement across different motor and driver setups.
• Simplicity: Once understood, it can simplify the configuration process, especially for complex geared systems.

Calculating for Extruders (Calibration Method)

For extruders, achieving the perfect rotation_distance is often a matter of calibration rather than pure calculation from physical parameters. This is because factors like filament diameter tolerance, hob gear grip, and nozzle back pressure can subtly affect the actual amount of filament extruded. The goal is to ensure that when Klipper commands 100mm of extrusion, exactly 100mm of filament is pushed through.

Step-by-Step Extruder Calibration:

1. Prepare Your Printer:
   • Heat your hotend to printing temperature for your chosen filament (e.g., 200°C for PLA).
   • Ensure your filament is loaded and flowing smoothly.
   • Disable any pressure advance settings temporarily if you have them enabled.
2. Mark the Filament:
   • Measure exactly 120mm from a fixed point on your extruder (e.g., where the filament enters the extruder body) and make a clear mark on the filament.
3. Extrude Filament:
   • Using your printer's interface (or via G-code commands like G92 E0 then G1 E100 F60), command your extruder to extrude 100mm of filament.
   • Allow the extrusion to complete.
4. Measure the Remaining Filament:
   • Measure the distance from your fixed point on the extruder to the mark you made on the filament.
   • Subtract this measured distance from your initial 120mm mark. For example, if you measure 22mm remaining, your actual extruded amount is 120mm - 22mm = 98mm. This is your "Measured Extrusion Length".
5. Use the Calculator:
   • Enter your current rotation_distance value from your printer.cfg file into the calculator above.
   • Enter your "Desired Extrusion Length" (which was 100mm in our example).
   • Enter your "Measured Extrusion Length" (e.g., 98mm).
   • Click "Calculate New Extruder rotation_distance".
6. Update Klipper Config:
   • Take the "New rotation_distance" value from the calculator.
   • Edit your printer.cfg file, specifically the [extruder] section, and update the rotation_distance parameter.
   • Save and restart Klipper.
7. Verify (Optional but Recommended): Repeat the calibration process to confirm the new value is accurate. Ideally, your measured extrusion should now be very close to 100mm.

Calculating for Linear Axes (Initial Setup)

For linear axes like X, Y, and Z, the rotation_distance can often be directly calculated from the physical properties of your printer's motion system. This is typically a one-time calculation during the initial setup.

Lead Screw Driven Axes (e.g., Z-axis)

Many Z-axes use a lead screw to translate rotational motor movement into vertical linear movement. In a direct-drive lead screw system (where the motor shaft is directly connected to the lead screw), the rotation_distance is simply the pitch of the lead screw.

The pitch is the distance the nut moves for one complete rotation of the screw. Common lead screws include T8 lead screws with a pitch of 8mm (meaning 8mm of linear travel per rotation).

Formula:

rotation_distance = Lead Screw Pitch (mm)

Use the "Lead Screw" section of the calculator above by entering your lead screw's pitch.

Belt Driven Axes (e.g., X and Y-axes)

Most X and Y axes, and sometimes even Z axes, utilize a belt and pulley system. Here, the rotation_distance is determined by the circumference of the pulley's travel path, which is dependent on the belt pitch and the number of teeth on the pulley.

Common belt types are GT2 (2mm pitch) and GT3 (3mm pitch). Pulleys typically have 16, 20, or 36 teeth.

Formula:

rotation_distance = Belt Pitch (mm) × Pulley Teeth Count

Use the "Belt Drive" section of the calculator above by entering your belt's pitch and the pulley's teeth count.

Applying rotation_distance in Klipper Config

Once you have your calculated or calibrated rotation_distance values, you need to update your printer.cfg file. Each axis or extruder will have its own section.

Example printer.cfg Snippets:

[extruder]
step_pin: PC12
dir_pin: PB10
enable_pin: !PC11
rotation_distance: 22.67895  # Update this value after calibration
gear_ratio: 50:17           # If applicable
microsteps: 16
full_steps_per_rotation: 200
nozzle_diameter: 0.4
filament_diameter: 1.75
heater_pin: PB4
sensor_type: EPCOS 100K B57560G104F
sensor_pin: PA0
# ... other extruder settings ...

[stepper_x]
step_pin: PB9
dir_pin: PC2
enable_pin: !PB8
rotation_distance: 40       # For a GT2 belt, 20 tooth pulley (2mm * 20 teeth)
microsteps: 16
full_steps_per_rotation: 200
# ... other stepper_x settings ...

[stepper_y]
step_pin: PB7
dir_pin: PB6
enable_pin: !PC7
rotation_distance: 40       # For a GT2 belt, 20 tooth pulley (2mm * 20 teeth)
microsteps: 16
full_steps_per_rotation: 200
# ... other stepper_y settings ...

[stepper_z]
step_pin: PB5
dir_pin: PC3
enable_pin: !PB3
rotation_distance: 8        # For an 8mm pitch lead screw
microsteps: 16
full_steps_per_rotation: 200
# ... other stepper_z settings ...

Remember to save your printer.cfg file and issue a FIRMWARE_RESTART command in Klipper after making changes.

Important Considerations

• Microsteps and Full Steps: While rotation_distance abstracts these, ensure your microsteps and full_steps_per_rotation are correctly defined in your Klipper config for optimal motor performance and accuracy.
• Gear Ratios: If you have a geared extruder or axis, make sure the gear_ratio parameter is correctly set in Klipper. The rotation_distance calculation itself typically accounts for the final linear movement per motor rotation, but the gear ratio is vital for Klipper to manage the motor's actual steps. For extruder calibration, the gear ratio is implicitly handled by the empirical measurement.
• Precision: Use enough decimal places for your rotation_distance values (typically 3-5) to maintain high accuracy.
• Units: Always ensure all your input values are in millimeters (mm).

Conclusion

The rotation_distance parameter is a powerful and flexible feature of Klipper firmware. By accurately calculating and calibrating these values using the tools and methods provided, you can significantly improve the precision and reliability of your 3D printer's movements and extrusion, leading to higher quality prints. Happy printing!