How to Engrave Curved 3D Objects with a UV Laser

A UV laser at 355 nm does something fiber and CO2 lasers physically cannot: it marks transparent and heat-sensitive materials without burning them. Glass, clear acrylic, silicone, white plastics, anodized aluminum at color-stable settings, ceramic surface coatings, semiconductor wafers, and printed circuit boards all sit in the UV sweet spot.

Add a 3D dynamic-focus head to that UV source and the working area is no longer a flat plane. The beam tracks the geometry of a curved or stepped object, holding focus across height changes the lens alone cannot accommodate. That combination, UV cold marking plus 3D dynamic focus, is what makes high-end UV galvo systems uniquely good at engraving on rounded perfume bottles, watch case-backs, ceramic vials, headphone shells, signal-lamp lenses, and any other workpiece where the engrave surface dips and rises across the field.

This guide walks through the full workflow: calibrating the 3D dynamic-focus head, preparing a 3D model in CAD, exporting the right kind of STL file, importing it into the laser control software, dialing in cold-marking parameters, and executing a clean engraving on a real curved part.

Reading time: about 14 minutes. Plan 2 to 3 hours the first time you walk a brand-new 3D object through the whole sequence; under 30 minutes for the same job once you have CAD presets and laser parameter recipes saved.

Why UV cold marking on a 3D dynamic-focus head opens up materials other lasers cannot touch

The physics matter for what you can actually make. A UV photon at 355 nm carries about three times the energy of a 1064 nm fiber-laser photon. Above a material’s bond-energy threshold, that photon breaks chemical bonds directly rather than heating the material to a temperature where it bleaches, melts, or carbonizes. That direct-bond-breakage process is what the industry calls cold marking.

Cold marking matters when:

• The material is transparent (glass, clear plastics) and you want a contrast mark without internal cracking.
• The material is heat-sensitive (silicone, thin films, photoresist, pharmaceutical-grade plastics) and a thermal mark would deform or discolor the workpiece.
• The material is a coating you want to selectively remove without damaging the substrate underneath (anodized aluminum, painted ceramic, printed labels).
• The workpiece carries electronic components that cannot tolerate localized heat (PCBs, sensors, MEMS devices).

A fiber laser at 1064 nm does the opposite, depositing thermal energy into a tight spot. Excellent for metal marking. Wrong tool for the materials above.

The 3D dynamic-focus head adds a second axis of capability. A traditional galvo head plus a single focal-length lens focuses at one fixed working distance. If your workpiece is curved, the bottom of the curve and the top of the curve sit at different distances from the lens, so only one band of the engraving will be in true focus. The rest is soft.

A 3D dynamic-focus head solves this by adjusting beam focal length in software, on the fly, as the galvo mirrors point the beam at each different position on the workpiece. As the beam crosses a curved surface, the dynamic-focus optics track the surface height so the spot stays sharp everywhere.

For a UV galvo with a 3D dynamic-focus head, the result is a marking system that can engrave a 12 mm tall logo around a 30 mm diameter perfume bottle, in glass, without rotating the bottle and without losing focus on either the top or the bottom of the logo. Or a serial number on a curved watch case-back. Or a barcode that wraps a 6 mm ceramic vial.

What “3D engraving” actually means on a UV laser

The 3D in “3D engraving” is sometimes confusing. There are two distinct things people mean by it:

3D surface engraving on a 3D object is what this guide covers. Your design is a 2D vector or raster image (a logo, a serial number, a barcode), but you are projecting it onto a 3D surface that varies in height across the working area. The 3D dynamic focus tracks the surface height so the beam stays at true focus everywhere; the design itself is still 2D in topology.

3D relief engraving is the much rarer case where the design has actual depth, like a coin where different parts are engraved deeper to create relief. This is a multi-pass process where each pass engraves to a different depth. Most UV galvo systems can do this for shallow reliefs (under 1 mm); deep relief is fiber-laser territory.

This guide focuses on the first case (3D surface engraving). The workflow is the same for both, but parameter sets and pass counts differ.

What you need before you start

A UV galvo with a 3D dynamic-focus head. On the JPT catalog this is the optional Feeltek FR10-U 3D dynamic-focus upgrade (USD 5,500 add-on — up to a 600 x 600 mm field, with focus steered in software and no field lens) installed on any of our UV machines: the 5W Lark-355-5A air-cooled, 10W Seal-355-10S, 15W Seal-355-15S, or 20W Seal-355-20S. A standard fixed-focus UV galvo can do flat-surface UV marking but cannot track a curved workpiece. If your workpiece is flat (cards, panels, name tags) you do not need the 3D upgrade.

A workpiece holding jig. Curved objects need to sit in a predictable position so the 3D height-map matches the actual physical geometry. A simple V-block, machined cradle, or custom 3D-printed fixture is enough.

A CAD program that exports STL. Autodesk Fusion 360 is the standard for this workflow because it is free for personal use, handles unit conversion cleanly, and produces clean STL exports. Onshape, SolidWorks, FreeCAD, and Inventor all work too.

The laser native 3D control software. LenMark is Feeltek’s controller-side software for the 3D dynamic-focus head. On fiber machines, EZCad 3 handles 2.5D Z-control (a fiber-only feature — UV machines run EZCad 2 and have no 2.5D path); for full 3D dynamic focus on a Feeltek head, LenMark is the software you use.

Physical measurement tools. Digital calipers for measuring the workpiece dimensions, a height gauge or motorized Z reading for setting the reference focal plane.

Test material. A few practice copies of the actual workpiece (or a similar geometry) for parameter testing before you commit to the production piece.

Step 1: Calibrate the Feeltek 3D dynamic-focus head

A 3D dynamic-focus head adjusts focal length on the fly. For that adjustment to be accurate, the software needs to know exactly what the maximum and minimum focal distances are for your current lens, and where the zero reference plane sits relative to your physical work surface.

The first-time calibration:

1. Mount the lens you will be using. Note the focal length.
2. Place a flat reference card (an aluminum business card works) on the work surface.
3. Use the fire-and-listen test (covered in our lens focus and LightBurn calibration guide) to find true focal height at the work surface. Lock that as your reference Z=0.
4. In LenMark, set Z=0 to that motor position.
5. Move the head up and down through its travel range. The 3D dynamic focus has a finite z-range (typically plus-minus 10 to 25 mm depending on the head model). Verify the range in software matches the actual range the head can travel.
6. Save the calibration to the active LenMark profile.

This calibration is per-lens. If you swap lenses, repeat the sequence. Save the calibration for each lens so future swaps are a one-click profile load.

The 3D dynamic-focus head can lose accuracy if the lens is removed and re-mounted slightly off-axis. After any mechanical work on the head, redo the focal calibration on a flat reference before processing curved parts.

Step 2: Slice your 3D model in CAD (Fusion 360 workflow)

This is the critical step that separates a clean 3D engraving from a software crash.

The problem: LenMark uses your 3D model as a height map. The software wraps the design onto the surface of that height map and computes the dynamic focus correction for each point. If you feed LenMark the entire 3D model (every surface of the workpiece, all the way through), the mesh has tens of thousands of triangles describing geometry the laser will never touch. LenMark slows down dramatically, hangs, or crashes.

The fix: in CAD, slice the 3D model so you export only the specific surface the laser will actually engrave.

In Fusion 360:

1. Open the 3D model of your workpiece.
2. Identify the surface you want to engrave (the top of a curved cap, the side of a cylinder, etc.).
3. Draw a 2D rectangle on a plane parallel to the surface, sized slightly larger than your design footprint.
4. Extrude that rectangle through the workpiece, with the operation set to Cut.
5. The result is a sliced model that contains only the surface geometry the laser needs to map.
6. Save the sliced model as a new Fusion file (do not overwrite the original).

This single step is the difference between a 30 KB STL that imports in seconds and a 30 MB STL that locks up the control software.

If your workpiece is highly curved (like a sphere or a complex organic shape), you may need multiple slices for different engraving areas. Each engraving area gets its own slice and its own STL export.

Step 3: Export the STL at Medium Refinement

The STL file format triangulates the surface into a mesh. The number of triangles is controlled by the Refinement setting in the exporter.

The right setting is Medium Refinement. Not Fine, not High, not Custom-with-thousands-of-segments. Medium.

The reason: LenMark processes the STL by walking the mesh and computing focus corrections per triangle. Higher refinement means more triangles, which means more computation per second of laser fire, which means the software runs slower (or stops responding entirely).

Medium Refinement produces enough triangle density to represent the curved surface accurately to within fractions of a millimeter, while keeping the file under 1 MB for most workpieces.

In Fusion 360:

1. Right-click the sliced model in the browser tree.
2. Select Save As Mesh.
3. Format: STL.
4. Refinement: Medium.
5. Units: millimeters (verify this; if you work in inches in Fusion, the laser software expects millimeters and will mis-scale unless you set this explicitly).
6. Click OK and save the .stl file to a known location.

Verify the file is under 1 MB. If it is larger, your Refinement is too high. If it is under 50 KB, you may need to step up to Medium-Fine for a smoother curve representation. Most workpieces land in the 100 KB to 500 KB range at Medium.

Unit-matching is non-negotiable. If your CAD exports inches and LenMark expects millimeters, your model will be 25.4 times the size on import. The design will be off the workpiece before you fire the first pulse. Always verify units twice.

Step 4: Import to LenMark and wrap the design

With the optimized STL in hand:

1. Open LenMark.
2. Import the .stl file. The software loads the mesh and renders the surface as a 3D wireframe.
3. Position the mesh at the X, Y, Z coordinates that match the physical workpiece on the laser bed. This is where the workpiece jig matters: a known position translates directly to a known coordinate in the software.
4. Import or paste your 2D design (the logo, serial, barcode) as a vector or bitmap.
5. Use LenMark’s surface-wrap function to project the 2D design onto the 3D mesh. The software calculates the per-triangle focal correction so the design will engrave at correct scale across the curved surface.
6. Preview the wrap. The design should follow the curve naturally; if it stretches, scales unevenly, or misses parts of the surface, the wrap parameters need adjusting (typically the projection direction or origin point).
7. Once the wrap looks right, save the LenMark project.

If you are engraving the same workpiece type repeatedly (a production run on identical bottles or watch cases), save the wrapped project as a template. Future runs become open-template, swap-design, fire.

Step 5: Dial in UV cold-marking parameters

Cold marking on UV is parameter-sensitive. Too much power and you start ablating instead of marking (the surface heats up enough to behave like a thermal mark). Too little and you barely break the surface. The right window is narrow.

Starting parameters for common materials at 5 to 20 W UV:

Glass (clear or frosted): Power 30 to 50 percent, frequency 30 to 60 kHz, speed 1000 to 2000 mm/s, 1 to 2 passes.

Anodized aluminum (color-preserving mark): Power 15 to 30 percent, frequency 40 to 80 kHz, speed 1500 to 3000 mm/s, 1 pass.

White or colored ABS/PC plastic: Power 20 to 40 percent, frequency 30 to 50 kHz, speed 800 to 1500 mm/s, 1 pass.

Silicone: Power 25 to 45 percent, frequency 30 to 50 kHz, speed 600 to 1200 mm/s, 1 to 2 passes.

These are starting points, not recipes. The exact values depend on your specific source power, lens focal length, and material lot. The standard practice is to burn a parameter test grid (a 5×5 matrix of identical designs at different power-and-speed combinations) on a scrap piece before committing to the production part.

Step 6: Run the engraving and verify

With calibration, slicing, STL, wrap, and parameters dialed in, the actual engraving is the easy part.

1. Place the workpiece in the jig at the calibrated position.
2. Lower the laser shroud and verify the interlock.
3. Run a focus check: fire a single dot at one corner of the design area, visually confirm the spot is sharp.
4. Run a preview trace (laser off) to verify the design path is on the surface.
5. Fire the engraving.
6. After the run, inspect with a jeweler’s loupe or USB microscope. Check edge crispness, depth uniformity, and surface contrast.

If the result looks soft at one edge but sharp at another, the 3D focus calibration may be slightly off for that part of the surface. Re-run Step 1 with extra attention to the calibration range.

If the result looks burnt or yellowed, you are in the thermal-marking regime, not cold-marking. Drop power 10 percent and re-test.

Common mistakes that ruin 3D UV marks

• Exporting STL at High or Fine refinement because “more detail is better.” LenMark becomes unusable. Always Medium.
• Forgetting to slice the model in CAD before exporting. The full closed mesh imports but slows the software to a crawl.
• Mis-matched units in CAD export. Always verify millimeter export when LenMark expects mm.
• Skipping the 3D focus calibration after a lens swap or any mechanical work on the head. The dynamic focus quietly drifts and you only see it as edge-of-field softness in your engravings.
• Running production parameters on glass without a test grid. Glass varies more lot-to-lot than other materials; what worked on last week’s bottle batch may need adjustment for this week’s.
• Treating UV cold marking like fiber marking. They are different physical processes. UV parameters are typically lower power and higher speed than fiber for the same visual mark.
• Using a fixed-focus head for a curved workpiece and wondering why one edge of the engraving is soft. The fix is the dynamic-focus head, not parameter tuning.

JPT-specific notes

A few details that matter on the JPT UV catalog specifically:

Four UV power tiers cover the working envelope.

• 5W Lark-355-5A is air-cooled, the smallest and most portable. Right for low-volume bespoke work like custom watches and one-off luxury packaging.
• 10W Seal-355-10S is water-cooled, the entry production tier. Right for steady glass engraving and small-batch electronics marking.
• 15W Seal-355-15S is water-cooled at higher production speed. Right for full-shift production of glass, ceramic, and plastic parts.
• 20W Seal-355-20S is the flagship UV. Right for continuous production marking on demanding materials. Slight pulse-to-pulse stability tradeoff versus the 15W; details on the product page.

The Feeltek 3D dynamic-focus head is an optional upgrade, not standard. The base UV machines ship with the standard Sino-Galvo SG7110 head and a fixed-focus lens. The 3D head is a USD 5,500 add-on at order time, replacing the standard head in the optical assembly. If you know at purchase that you will engrave curved 3D objects, configure the upgrade at checkout. Adding it later means shipping the head as a service exchange, which is doable but takes time.

Included accessories. Every JPT UV machine ships with two field lenses of your choice (70, 110, 175, 210, or 300 mm focal length), one rotary of your choice (D60, D80, or D100), a motorized Z-axis, UV-rated safety glasses, and a foot pedal. The rotary and Z-axis included as standard differentiate our UV machines from most production UV systems where those are upsell items.

EZCad 2 versus LenMark. Every UV machine ships with EZCad 2 and a motorized Z-axis: for stepped or terraced workpieces you set focus per height level with the motorized Z and run the pass — there is no 2.5D software path on UV (EZCad 3 with 2.5D Z-control is a fiber-only upgrade). LenMark drives full 3D dynamic focus on the Feeltek FR10-U head. They solve different problems. For a curved workpiece you want LenMark and the 3D head; for stepped workpieces, EZCad 2 plus the included motorized Z is sufficient.

More on JPT source grades. UV catalog uses DPSS Q-switched nanosecond architecture across all 4 tiers. The naming convention (Lark vs Seal, air vs water cooling) and cooling requirements are explained on each product page; broader JPT source-grade taxonomy is in our JPT source grades explained pillar.

FAQ

Predictable 3D UV marks, repeatable production

A UV galvo with a properly calibrated 3D dynamic-focus head, fed clean sliced STL files and dialed-in cold-marking parameters, produces marks on curved glass, ceramic, plastic, and coated metal that no fiber or CO2 laser can match. The workflow is finicky on the first run and routine after that.

If you are evaluating UV machines for 3D engraving work, our help me choose walkthrough narrows the 4-tier UV catalog to the right fit for your application volume. If you have a specific 3D engraving job and want to talk parameters with a JPT engineer before ordering, email info@jpt-laser.com.

Related guides: How to focus a fiber laser lens and calibrate it in LightBurn covers the focus fundamentals applicable to all galvo systems including UV.