Preparing STL Models For Internal Glass Engraving

Merging 3D Models for Sub-Surface Laser Engraving (SSLE)

If you’ve ever tried to engrave multiple 3D models inside a glass block, you’ve likely seen "burn clouds" where the objects overlap which happens because the laser fires twice at the same coordinates. You may also see murky looking areas where there are too many layered surfaces distracting your focus on the outer surfaces. This is likely from inner features of the 3D models that might exist for other processes like 3D printing. To get a professional, crystal-clear result, you must merge your 3D files into a single, hollow shell.

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Follow this professional workflow to prep your STL files for xTool Studio or any SSLE software. We can make our edits using the free version of "Blender" using the download link below:

✅ Download — Blender

Step 1: Fix Your Units

STL files don't actually know what a "millimeter" is; they only see numbers. To ensure your 80mm model doesn't show up as a microscopic 0.08mm speck or as large as a 30 storey building, you must set your Unit Scale correctly.

1. File > Import > STL and import your models. If the files were created in Blender they may import into the correct locations. If not, you may need to use the Move tool to manually move the pieces around such that they slightly overlap one another for the best results.
   
   
2. Once you are satisfied with the position, Join the Objects: Select all your parts and press Ctrl + J.
   
   
3.  Use the Measure tool to measure your single part, or press N on the keyboard to bring up the Transform tool bar and you can see the dimensions and units.
   
   

4. Go to the Scene Properties tab (the icon with a cone and a sphere).

5. Set Unit Scale to 0.001. (This tells Blender that 1 internal unit = 1 millimeter).

6. Set Length to Millimeters.

7. Scale & Apply: Select your models and press S to scale them to around your crystal size (e.g., 80mm tall).

8. CRITICAL: Press Ctrl + A and select Apply Scale. Your scale values in the sidebar must read 1.000.

Step 2: Voxel Remeshing

Standard "joining" leaves internal walls inside the model. We need to "shrink-wrap" a new skin over the parts to delete everything inside.

1. Enter Sculpt Mode: Switch from "Object Mode" to "Sculpt Mode" in the top-left dropdown.

2. Visual Voxel Grid: Press Shift + R. A grid will appear. Move your mouse until the squares are tiny—roughly 0.05mm for high detail. This gives you a concept of how small your finest details are in your model.

3. Object Data Properties: Open the object data properties window by clicking the tab on the bottom right side of the screen that looks like a blue triangle. Use the remesh dropdown in the top right corner of the workspace and select the eyedropper tool. Click on the model and the voxel size value will update in the object data properties tab. Do this several times to find the smallest voxel number. Divide the number in half and manually enter it in the object data properties voxel size window.
   
   

4. Execute: Click to confirm the size, then press Ctrl + R to run the Remesh. All internal overlaps are now gone as long as the bodies are properly intersecting with one another.

Step 3: Shrink the File Size (Decimation)

Remeshing often creates 5–10 million faces, which could crash some laser software and create unnecessarily large file sizes. We need to simplify the mesh while keeping the detail.

1. Add Modifier: Go to the Modifiers Tab (Blue Wrench) and add Decimate.

2. Set Ratio: If you have 6 million faces and want 1.5 million, set the Ratio to 0.25. (You may have to go lower - it is not always exactly this precise).

3. Apply: Click the arrow on the modifier and select Apply. Aim for a final count under 2 million faces for smooth performance.

Step 4: The "Watertight" Check

A 3D model ideally should be "manifold" (closed) mesh to know where the inside of the shape is.

1. Enable the 3D-Print Toolbox in Edit > Preferences > Add-ons.

2. In the sidebar (N), click 3D-Print > Check All.

3. The Clean-Up: If you have errors such as non-manifold edges, enter Edit Mode ( Press Tab), select all (A), and do this:

   • Merge by Distance: Press M > Merge by Distance (removes duplicate points).

   • Recalculate Normals: Press Shift + N (ensures the "skin" faces outward).

   • Degenerate Dissolve: Go to Mesh > Clean Up > Degenerate Dissolve (removes zero-width faces).

Pro-Tip: Turn on Face Orientation in the Overlays menu. If your model is Blue, it’s healthy and the face normals are pointing outwards. If you see Red, those faces are pointing inside-out and could be a problem... Generally this part of the process is not critical for dotting and scanning engraving methods. It could be more useful for solid engraving as the software may be more picky about a properly defined volume inside the model.

Step 5: Exporting for Success

When you export, these settings ensure your dimensions stay exactly as you designed them.

1. Go to File > Export > Stl (.stl).

2. Export Settings:

   • Check Selection Only.

   • Check Apply Modifiers.

   • Verify Scale is set to 1.0 (since we fixed the Unit Scale in Step 1).

3. Import: When you bring this into xTool Studio, it should appear at the perfect size, with zero internal overlaps, ready for a flawless engraving.