How to Use Override PWM Frequency to Optimize Cutting and Engraving Quality

How to Use Override PWM Frequency to Optimize Cutting and Engraving Quality

Preface

In the world of precision laser processing, "Power" and "Speed" are not the only variables that determine the quality of your work.
For users of high-end RF (Radio Frequency) laser tubes, the PWM Frequency is a "secret weapon" that can significantly impact edge smoothness, charring, and detail clarity.

This article will explain how to optimize your results by mastering the Override PWM Frequency setting in LightBurn.

1. Understanding and Applying Override PWM Frequency in LightBurn

1.1. What is Override PWM Frequency

Override PWM Frequency is an advanced control feature in LightBurn designed for machines with Ruida controllers and RF tubes.

PWM (Pulse Width Modulation) controls how many times the laser pulses per second. While the "Power " determines how long the laser stays on during each pulse (duty cycle), the "Frequency" (measured in kHz) determines how many pulses occur in a given timeframe. By using the "Override PWM Frequency" function, you bypass the controller’s default frequency and tailor the laser’s firing behavior to the specific material you are processing.

Notes
This feature is exclusive to RF (Radio Frequency) tubes (like those from SPT, Coherent, or Iradion). Standard DC glass tubes do not support this type of high-frequency modulation.

1.1.1. Modulation Parameters for Thunder Laser RF Tubes

Before adjusting settings, it is crucial to know the operating range of your hardware. Exceeding these limits or using incorrect settings can lead to suboptimal performance.

RF Tube Brand/Model

Modulation Range

SPT 30W

0.1 ~ 25 KHz

SPT 60W

0.1 ~ 50 KHz

SPT 80W

0.1 ~ 50 KHz

Coherent 30W

0.1 ~ 200 KHz

Coherent 55W

0.1 ~ 200 KHz

Iradion 50W

0.1 ~ 140 KHz

Iradion 80W

0.1 ~ 140 KHz

Notes
Some RF laser brands have not been tested yet, so their default parameters are currently unknown.
To check the default frequency for your laser type, please go to Machine Settings in LightBurn and click Read to load the manufacturer parameters.  


1.2. Why Optimizing RF Laser Tube Frequency Matters

Adjusting the frequency allows you to control the Heat Affected Zone (HAZ) and the way energy is delivered:

Impact

Explanation

  • Edge Quality

In cutting (especially acrylic), higher frequencies create a more continuous melt, resulting in a "flame-polished" glass-like edge.

  • Reduced Charring

For organic materials like wood or paper, lower frequencies can reduce heat accumulation, leading to less burning or discoloration.

  • Detail Precision

In engraving, matching the frequency to the speed and DPI prevents "dotted"

lines and ensures smooth gradients.
  • Machine Longevity

Operating within the optimized frequency range of the RF tube prevents unnecessary stress on the RF power supply.


1.3. How to set Override PWM Frequency

Follow these steps to enable and adjust the frequency for a specific layer:

Step 1: Open Layer Settings

Double-click the layer (color) in the "Cuts / Layers" window.

Step 2: Select Advanced Mode

Ensure you are in the "Advanced" tab (though in recent LightBurn versions, it is often visible in the main Cut Settings editor for Ruida controllers).

Step 3: Enable "Override PWM Frequency

Find the checkbox labeled "Override PWM Frequency".

Step 4: Input Value

Enter the desired value in kHz (e.g., 20).


  • Tip: Ensure the value is within your laser tube’s specific range mentioned in the table above.


The general rule is: Higher Frequency = More Heat/Continuous Output; Lower Frequency = Less Heat/Pulsed Output.

If you don't want to do too many tests, you may process the material using the parameter settings from the material library in the link below, based on your machine model.

Material Libraries and Safe/Unsafe Resources
You can download the Library file and import it into the Material Library in LightBurn.


Recommended parameter settings for common materials:
Notes
All materials below were tested using a Nova Plus 35–60W machine.
Adjustable frequency ranges vary between different RF laser brands and models, so actual processing results may differ. 

1.4.1. Plywood (Cutting & Engraving)

  • Cutting: 1 KHz – 10 KHz (Lower frequency reduces the "charcoal" effect on the edges).


  • Engraving: 14-25 KHz (Provides a smooth, consistent brown tone).


1.4.2. Paper and Cardstock (Cutting)

  • Recommended: 1 KHz – 5 KHz
  • Why: Very low frequency minimizes the heat-affected zone, preventing the edges of delicate fabrics from melting too much or paper from catching fire.


1.4.3. Anodized Aluminum (Engraving)

  • Recommended: 20 KHz – 25 KHz
  • Why: High frequency is needed to achieve a clean, white mark on the anodized layer without damaging the metal underneath.


1.4.4. Leather (Engraving)

  • Recommended: 14 KHz – 25 KHz
  • Why: High-quality engraving suitable for fine textures, uniform depth, and smooth edges.


2. Important Notes

The above settings and test results are for reference only. Users should test and adjust parameters based on the material and laser type to achieve optimal results.

  • Start with Defaults: Always start your testing at the manufacturer's default (usually 25 KHz). Only adjust if you see issues like excessive charring or "dotted" cut lines.
  • Listen to the Tube: RF tubes often emit a high-pitched hum. This is normal, and the pitch will change as you adjust the PWM frequency—this is the sound of the gas being excited at different rates.


3. Still need help?

For specific technical questions or help requests, please open a Ticket with picture or video, so our Support team can assist you ASAP.

For the information provided in the ticket, please refer to this link：

Help Tech Support Troubleshoot Faster


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