Fine-Tune Flow Rate Calibration Guide

Calibrating your flow rate (also called extrusion multiplier) ensures that your printer extrudes the right amount of filament, leading to dimensionally accurate and high-quality prints. This guide will show you how to fine-tune your flow rate step by step.

What is Flow Rate?

The flow rate controls how much filament your printer extrudes for a given movement. An incorrect flow rate can cause:

• Over-Extrusion: Excess filament, resulting in blobs, uneven layers, or dimensional inaccuracies.
• Under-Extrusion: Insufficient filament, leading to weak layers, gaps, or poor layer bonding.

Why Fine-Tune Flow Rate?

Accurate flow rate calibration ensures:

• Precise Dimensions: Prints match the design’s intended size.
• Improved Surface Quality: Smooth and consistent layers.
• Strong and Durable Parts: Proper layer bonding without over-extrusion.

How to Calibrate Flow Rate

1. Prepare Your Printer

• Use the filament you want to calibrate.
• Ensure your nozzle is clean and the bed is leveled.
• Set a consistent print temperature, ideally the optimal temperature identified using a temperature tower.

2. Print a Flow Cube

A flow cube is a hollow cube (typically 20x20x20mm) with no infill. It allows you to measure the thickness of the walls to check extrusion accuracy.

1. Download or create a flow cube model.

2. Set your slicer to:

   • Single perimeter walls (1 extrusion width thick).
   • No infill.
   • No top layers.

3. Print the cube and let it cool before measuring.

3. Measure the Wall Thickness

• Use a digital caliper to measure the thickness of each wall.
• Compare the measured thickness to the intended wall thickness (e.g., 0.4mm for a 0.4mm nozzle).

4. Calculate the New Flow Rate

Use this formula to adjust the flow rate:

New Flow Rate=Current Flow Rate×(Intended Wall ThicknessMeasured Wall Thickness)\text{New Flow Rate} = \text{Current Flow Rate} \times \left( \frac{\text{Intended Wall Thickness}}{\text{Measured Wall Thickness}} \right)New Flow Rate=Current Flow Rate×(Measured Wall ThicknessIntended Wall Thickness​)

For example:

• Current flow rate = 1.00 (100% in your slicer).
• Intended wall thickness = 0.4mm.
• Measured wall thickness = 0.45mm.

New Flow Rate=1.00×(0.40.45)=0.89\text{New Flow Rate} = 1.00 \times \left( \frac{0.4}{0.45} \right) = 0.89New Flow Rate=1.00×(0.450.4​)=0.89

5. Update Your Slicer Settings

• In PrusaSlicer, go to Filament Settings > Filament Overrides > Extrusion Multiplier and enter the new flow rate.
• Save your updated filament profile for future prints.

Tips for Accurate Flow Rate Calibration

• Measure multiple walls and take the average to reduce measurement errors.
• Use a fresh cube for each test to avoid skewing results.
• Keep your filament diameter consistent. Measure it with calipers and input the average in your slicer settings.