How to select the appropriate glass?

1. Glass tolerance and chamfers

What is the impact of glass tolerance?

Glass typically has a ±2 mm tolerance (due to cutting, grinding, and polishing), so accurate measurement is required before processing. Tolerance may cause slight positional or shape deviations in the processed model.

Why does glass have chamfers?

Glass is a hard and brittle material that is prone to minor chipping at the edges during processing. This is why it features protective chamfers.

2. Glass types that do not support inner engraving or have poor inner engraving results

The most widely used glass for inner engraving is K9 glass, which is well-suited for laser inner engraving processes and delivers ideal results.

Laser inner engraving relies on high-energy lasers to form micro-fracture points inside the glass, creating patterns through light scattering. This process demands extremely high purity, uniformity, and structural stability of the glass. The following types of glass are not suitable for inner engraving or yield poor results:

• Tempered glass: Due to high internal stress, the micro-fracture points triggered by the laser can lead to breakage of the whole glass.
• Laminated glass: The middle interlayer absorbs and reflects the laser, preventing the precise formation of micro-fracture points and potentially causing delamination.
• Deeply tinted glass: The colorants in the glass absorb a large amount of laser energy, making it difficult to form clear and uniform patterns.

3. Variations in glass of the same material type but different grades

• Impact of optical uniformity: Defects such as internal streaks, bubbles, and impurities in glass can cause laser scattering or abnormal energy at the focal point, resulting in uneven engraving or even failure to engrave. High-quality materials tend to have fewer defects, and it is recommended to inspect the glass before processing and ensure the engraving pattern avoids defect areas as much as possible.
• Impact of uneven internal stress: During the melting and forming process, uneven melting temperatures, improper cooling, or annealing techniques can create internal stress in the glass. Additional stress can also be introduced during subsequent processes such as cutting, grinding, and polishing. Uneven internal stress causes birefringence in the glass when exposed to lasers, affecting focus and energy deposition, which in turn impacts the engraving results.
• Impact of surface roughness: Microscopic unevenness on the glass surface can cause laser scattering or distortion before the laser enters the glass. This distortion affects the shape and energy distribution of the focused beam at the intended point inside the glass. Consequently, this may lead to insufficient energy at the engraving point, unclear markings, or a complete failure to form the engraving.

How to determine the refractive index of glass?

1. What is refractive index?

Refractive index is an important physical quantity that describes the difference in the speed of light as it travels through different mediums. When light passes from one transparent material to another, its direction changes—a phenomenon known as refraction. The higher the refractive index, the slower light travels within the material, and the more pronounced the refraction.

In everyday glass materials, the refractive index varies among different types of glass. For example:

• Ordinary float glass: ≈ 1.50
• K9 optical glass: ≈ 1.51
• High-lead crystal glass: ranges from 1.6 to 1.9

2. Impact of refractive index on glass inner engraving

During the process of glass inner engraving, the refractive index being greater than 1 causes the laser path to bend as it enters the glass, resulting in a deviation between the theoretical focal point and the actual focal point. If the refractive index is not set correctly, it may lead to:

• Laser focal point deviating from the expected position
• Vertical displacement of the inner engraving location
• Unstable distance between engraving layers
• Overall distortion of the image

Therefore, correctly setting the refractive index of the glass is crucial to ensuring engraving precision.

3. How to measure and determine the refractive index of different glasses?

To accurately match the refractive index of different glasses, a simple and effective measurement method can be used. The steps are as follows:

Step 1: Set the refractive index to 1 and engrave a model with a fixed height.

In xTool Studio, temporarily set the refractive index to 1.0. Then, engrave a test model with a known theoretical height (H₀) inside the glass (such as a vertical column structure or a straight line).

Step 2: Measure the actual height of the engraved model.

After completing the operation, use a caliper or other measuring tools to measure the actual imaging height inside the glass (H₁). This height will differ from the theoretical height due to glass refraction.

Step 3: Calculate the refractive index.

The refractive index can be calculated using the following formula:

Where:

H₀ = The theoretical model height set in the software

H₁ = The actual height inside the glass obtained through measurement

How to perform inner engraving on non-standard shaped glass workpieces?

To correctly perform laser inner engraving on non-standard shaped glass workpieces (such as heart shapes, pentagrams, and polygons), follow the tutorial below.

1. Basic principle: Ensure that the laser beam always remains on the same plane.

Before performing inner engraving, regardless of the shape of the glass, a fundamental requirement must be met: the glass surface must remain level to ensure that the laser engraving points are located on the same plane.

• The glass must be able to lie flat.
• The contact surface should be stable and free of tilt.
• Ensure the contact surface with the machine is even.

As long as the glass can lie flat, its approximate rectangular envelope area can be determined using the software, allowing for normal inner engraving to proceed.

2. Fixtures can be used to frame irregularly shaped glass into a rectangle.

To facilitate the software in recognizing the dimensions of irregularly shaped glass, fixtures or auxiliary tools can be used to position the glass within a rectangular boundary.

Method 1: Use fixed fixtures

Place heart-shaped, pentagram-shaped, or other glass pieces into a matching rectangular fixture:

• The outer frame of the fixture is a standard rectangle
• The interior features a shape-matching groove

Method 2: Manually frame a rectangular boundary

If no fixtures specifically designed for irregularly shaped glass are available, you can:

• Lay the glass flat on the platform
• Use regular blocks or stoppers to create a rectangular area tightly surrounding the glass
• Ensure the rectangular boundary covers the maximum range of the glass

This will allow you to obtain the bounding rectangle dimensions of the glass.

3. Input the bounding rectangle dimensions and positioning information into the software.

If the rectangular area exceeds the riser and the positioning piece cannot be used, you can input the coordinates of the bottom-left corner of the rectangle for positioning.

After entering the dimensions and positioning information, the software will generate a rectangular frame to represent the bounding rectangle of the irregularly shaped glass.

You need to confirm:

• The size of the rectangle on the canvas ≈ The actual bounding rectangle size of the glass
• The bottom-left corner corresponds to the actual position of the glass on the riser
• All measurement units are correct (precision to the millimeter level)

4. Place the model at the desired inner engraving position, ensuring that the model size matches the effective engraving area of the glass.

Irregularly shaped glass edges are often narrower than their bounding rectangle, so pay attention to the following:

• Avoid placing the model too close to the outer edges.
• Engraving is not possible at the recessed points of irregular shapes.
• It is recommended to leave a 1–2 mm margin within the rectangular bounding frame.

After confirmation, you can proceed with the normal inner engraving process.