In laser cutting machine, the focal length of the lens is a critical parameter that dictates the quality and efficiency of your work. The choice between a short or long focal length lens depends entirely on the material you are working with and the desired outcome, whether it’s intricate engraving or cutting through thick materials.
Understanding Focal Length
The focal length is the distance from the lens to the point where the laser beam converges to its smallest and most powerful spot.
This focal point is where the cutting or engraving action happens. Different focal lengths alter the laser beam’s characteristics, such as the spot size and the depth of focus.
Short Focal Length: Precision and Speed on Thin Materials
A short focal length lens, typically around 1.5 to 2.5 inches, concentrates the laser beam into a very small, high-energy spot.
This high power density allows for faster cutting speeds and extremely fine, detailed engraving.
Use a short focal length lens for:
- High-speed cutting of thin materials: The concentrated energy is perfect for quickly slicing through materials like thin acrylic, leather, and fabric.
- Detailed engraving and marking: The small spot size allows for intricate designs and high-resolution photo engraving.
- Cutting complex contours: The focused beam can navigate tight curves and sharp angles with precision.
However, be aware of the limitations:
- Shallow depth of focus: The focused area is very short, which means the material must be perfectly flat to maintain focus and achieve a consistent cut.
- Not ideal for thick materials: The beam diverges quickly after the focal point, making it less effective for cutting through thicker stock.
Long Focal Length: Powering Through Thick Materials
A long focal length lens, typically 4 inches or more, produces a larger spot size but offers a significantly greater depth of focus.
This means the laser beam remains focused over a longer distance, allowing it to cut through thicker materials with a straighter edge.
Opt for a long focal length lens when:
- Cutting thick materials: The extended depth of focus ensures the beam remains effective throughout the material’s thickness, resulting in a clean, vertical cut. Materials like thick wood or acrylic are best cut with a long focal length lens.
- Working with uneven surfaces: The larger focused area is more forgiving of variations in material flatness.
- When a larger kerf (cut width) is acceptable: The wider beam will create a wider cut.
Consider the following trade-offs:
- Lower power density: The larger spot size means the energy is less concentrated, which may require a higher-power laser or slower cutting speeds.
- Less detailed engraving: The larger spot size is not suitable for fine, intricate engraving.
Quick Comparison: Short vs. Long Focal Length
| Feature | Short Focal Length | Long Focal Length |
|---|---|---|
| Spot Size | Small | Large |
| Power Density | High | Low |
| Depth of Focus | Short | Long |
| Best for | Thin materials, detailed engraving | Thick materials, cutting |
| Cut Speed | Faster on thin materials | Slower, but effective on thick materials |
| Edge Quality | Can be tapered on thick materials | Straighter on thick materials |