When working on subsurface engraving, a common concern among laser users is how close you can engrave to the edges of a crystal without risking cracks or damage. While operators aim for finer details and clearer outputs, other factors, such as safety margins, engraving depth, and point concentration, remain a huge concern. This Cockpit3D walkthrough aims to share recommendations based on real production experience that help to address these concerns among laser users.
Why Crystals Crack During Subsurface Engraving
The cracks that you see inside a crystal after engraving are not caused by engraving itself. It is caused by point concentration at a specific area. During subsurface engraving, the laser beam is focused through lenses and mirrors so that it reconverges at a precise point inside the crystal. The focal point generates enough heat to burn a microscopic fracture inside the crystal. Millions of such microfractures, when placed together, form the image that you see engraved inside the crystal.
The problem that leads to the formation of cracks inside the crystal arises when these points are burned too close to each other or too close to the crystal's surface. This space gradually weakens, causing the microfractures to melt and merge, which leads to cracks inside the crystal. These cracks can spread in some cases. It might not be seen immediately, but it can happen later during shipping or handling.
Recommended Safety Margins for Crystal Engraving
The first safety measure to reduce the risk of cracking close to the surface is to maintain a margin between the engraving and the crystal edges.
A commonly recommended margin is:
- 3 mm margin on X, Y, and Z axes for a standard crystal size, which can be changed according to your needs.
The Z-axis margin decides the engraving depth. It determines how deep inside the crystal the engraving begins. Keeping the engraving at least 3 mm away from the front and back surfaces helps prevent surface-related stress cracks.
For smaller items like keychains or thin accessories, 3mm margin may be too much considering the size of the crystal. In such cases, a 2 mm margin is often sufficient, as long as point spacing is not overly dense.
Bevels and facets give an aesthetic look to the crystal. While Cockpit 3D has default bevel settings that match the crystal produced at 3dcrystal.com, these margin settings can be changed or altered according to your wish.
Depth: How Far Inside the Crystal Is Enough?
You don’t necessarily need to engrave deeply to get a good-looking 3D image. As long as your engraving starts safely inside the crystal, around 2 to 3 mm from the surface of the crystal, you can achieve strong results without adding extra risk.
After conversion, if the image feels too flat, Cockpit3D allows you to stretch the scenes slightly along the Z-axis to add visible depth. This adds to the perception of depth without pushing points closer to the crystal’s surface.
Is It the Number of Points That Causes Cracking?
A common misunderstanding is that having more points in your point cloud file leads to cracking. But that’s not always the case. In reality, the issue does not depend on the number of points. It mainly depends on how close these points are to each other.
When point spacing is too tight:
- The area is weakened
- Points can melt into each other
- Microfractures can spread and turn into visible cracks gradually.
This is why you must be extra careful while tightening spacing for higher resolution. Many UV laser users find safe and reliable results by using slightly loose spacing, like 0.06 to 0.066mm. This is much more reliable than pushing the points too close together.
Do You Need to Pause the Laser to Cool It Down?
In most cases, pausing the laser is not necessary. For issues like cracks in a crystal, pausing the laser is not of any help, as cracks develop mainly due to incorrect point density or spacing. It will likely happen regardless of short pauses. Heat-related issues are better controlled through:
- Proper point spacing
- Adequate margins
- Correct power settings
Many laser systems let you pause and resume crystal engraving, but it is neither the right nor the reliable solution to prevent crystals from cracking.
Handling Curved Shapes with Light Maps
Margins become a bit more challenging to handle once you start working with curved shapes like hearts. Here, rectangular margins don’t follow the natural outline of the crystal. This is where light maps in Cockpit3D become helpful.
Light maps create a controlled fade toward the edges of the crystal. This helps in reducing point density near the perimeter of the crystal. Two key settings that control this behavior are:
- Blur radius: Decides on how wide the fading area is
- Fall-off exponent: Lets you set how quickly the points should fade out
A commonly used and safe combination is:
- Blur radius: 3
- Fall-off exponent: 0.5
This powerful combination creates a smooth and gradual fade that preserves the overall look of the image in the crystal. It also keeps points away from the edges of the crystal to prevent cracks.
FAQs
- What is the best safety margin that works well for most of the crystals?
A 3 mm margin on X, Y, and Z axes is a safe standard for most crystal sizes. They make the crystal look good - Can I engrave closer to the edge on small items?
Yes, for small items like keychains, you can engrave close to the edge by leaving a 2 mm margin, which is usually acceptable. - Is cracking caused by too many points?
No. Cracking is not caused by the number of points. It is mainly caused by how close the points are to each other and how tightly they are packed together. - Do I need to pause the laser to prevent heat buildup?
Generally no. Working on getting the right spacing and margins is more effective than pausing. - How do I protect curved crystal edges?
You can use light maps to fade point density near the edges of the crystal instead of relying on rectangular margins.