A custom gobo is only useful when its projected image stays clean. Small burrs, melted bridges, warped edges, and misplaced interior islands become much more visible after a profile spotlight enlarges the stencil. For thin stainless-steel gobos, the practical challenge is to create a mechanically stable pattern while limiting heat input and keeping the cut geometry within the projector’s optical tolerance.
This workflow covers metal gobo stencils, micro-bridge typography, thin stainless-steel shims, and coated dichroic glass. It does not cover projector rigging or CNC routing.
What a gobo does
“Gobo” is commonly understood as “goes before optics.” It is a patterned disc placed in the optical path of a gobo projector, usually a profile spotlight. The projector’s lamp or LED source illuminates the disc, while lenses focus and enlarge the pattern onto a wall, stage, floor, scenic element, or architectural surface.
A gobo therefore works as both a physical stencil and an optical image-forming element. The disc must fit the projector’s holder, remain sufficiently flat under operating heat, and preserve the open and blocked areas of the design.
Common gobo size classes
Gobo size names are not interchangeable with outside diameter. Confirm the projector’s holder and the usable image area before designing the disc.
The disc diameter is only one constraint. The projector’s optical path, holder depth, focal position, and image enlargement determine how much of the design can be used without clipping or losing focus.
A logo that looks acceptable at the cutting table may show weak connections, blocked counters, or rough contours once projected. Treat the stencil as a small optical component rather than an ordinary decorative cutout.
Design the pattern for projection
The first design decision is whether the artwork can survive conversion into a stencil. Letters such as “A,” “B,” “D,” “O,” “P,” and “R” contain interior islands. If those islands are not connected to the surrounding structure, they will fall out of the metal or remain unsupported during handling.
Add structural bridges before sending the file to the laser. In LightBurn, convert text to paths, inspect every enclosed counter, and connect isolated regions with narrow tabs. For fine gobo work, the brief’s target range is approximately 0.2–0.3 mm per bridge.
A bridge should be placed where it causes the least visual interference:
-
Use a stroke or contour location that is already visually quiet.
-
Avoid placing bridges across the most recognizable part of a letter or logo.
-
Distribute supports rather than concentrating them on one side of an island.
-
Keep bridge geometry consistent enough that the disc remains balanced.
-
Inspect the projected result, not only the vector file.
The narrowest bridge is not automatically the best bridge. A bridge that barely survives cutting may deform during cleanup or installation. A wider connection is mechanically stronger but can create a more visible shadow line. The correct compromise depends on the projected image size, the artwork, the material thickness, and the projector’s focus.
Account for optical enlargement
Projection magnifies fabrication defects. A rough edge, a small notch, or a bridge that is slightly misplaced can become obvious on the projection surface. The practical effect depends on the projector’s optics and throw distance, but a defect that is insignificant at the disc may become prominent after substantial enlargement.
This is why gobo artwork needs a larger design margin than a simple metal stencil. Examine:
-
The minimum width of negative spaces.
-
The distance between adjacent cuts.
-
The shape and position of every bridge.
-
The radius of tight internal corners.
-
The relationship between the artwork and the disc edge.
-
Whether the projected image is intended to be crisp, soft, or intentionally distressed.
Keep the design centered and avoid placing critical details near the holder’s clamping or masking region. If the projector crops the edge of the disc, that may be acceptable for a simple texture but undesirable for a logo or monogram.
Cutting 0.1 mm stainless steel
Thin 304 stainless-steel shim stock is attractive for gobos because it is thin and resistant to heat compared with many temporary stencil materials. The same thinness that makes it useful also makes it easy to distort. A small amount of localized heat can pull an edge out of plane or weaken a micro-bridge.
High-power optical energy and a tightly compressed focal spot are important for piercing thin stainless steel and producing fine vector cuts. TwoTrees’ stainless-steel and jewelry-marking material discusses compressed optical spots and the interaction between focused laser energy and stainless steel. The specific machine configuration, optical source, material, and process settings still need to match the intended operation.
A 40 W diode system with a compressed spot or a 1064 nm fiber laser may be relevant for thin stainless-steel work, but the source should not be treated as a universal solution for every metal, thickness, or gobo design.
Flatten the shim first
Thin stock must remain flat throughout the cut. Pin the shim against a honeycomb bed with suitable magnetic hold-downs, keeping the magnets outside the laser path and away from moving components. The goal is to prevent the sheet from lifting into the gantry or nozzle while the toolhead moves.
Before cutting, check that:
-
The sheet lies flat across the entire design area.
-
Hold-downs do not obstruct the cut lines.
-
The work surface is stable and clear of loose metal fragments.
-
The laser head has adequate clearance over the secured material.
-
The material identity and thickness are known.
Do not hand-hold a shim near an active laser. A loose sheet can shift, catch airflow, or rise into the moving assembly.
Use conservative thermal control
The brief specifies high power, high frequency, and maximum air-assist pressure for piercing thin shims. Those values should be treated as starting directions from the supplied brief, not as a universal recipe. Cutting behavior changes with the laser source, focal geometry, air system, sheet condition, workholding, and vector layout.
The objective is not simply to increase power. It is to deliver enough energy to complete the kerf while minimizing the time that heat remains concentrated in a bridge or narrow web.
Use a small test pattern that includes:
-
A straight line.
-
A tight inside corner.
-
A representative letter counter.
-
One or two bridges at the intended width.
-
A short perimeter segment.
Inspect the underside as well as the visible face. A cut that appears open from above may still contain attached slag or a partially pierced section underneath.
Why active air assist matters
Active air assist directs a controlled flow toward the interaction zone. The supplied TwoTrees air-assist material describes airflow as helping clear smoke and vaporized material from the kerf and reducing localized heat buildup. In thin stainless steel, that function matters because molten or vaporized material can remain near a narrow bridge long enough to soften, reattach, or deform it.
Air assist helps by:
-
Clearing vaporized material from the cut path.
-
Reducing the amount of hot slag left in the kerf.
-
Limiting heat accumulation around small features.
-
Improving visibility of the cut zone.
-
Supporting cleaner separation of closely spaced vector paths.
It cannot compensate for an unsuitable focal position, excessive dwell time, poor workholding, or a design with bridges that are too narrow for the selected process. If a bridge melts, increasing airflow alone may not solve the problem; the energy distribution and geometry must also be reviewed.
Keep the focal plane consistent
Thin gobo stock has little thickness, but the cut still depends on the relationship between the focal point and the material surface. The brief identifies a target optical tolerance of approximately ±0.1 mm depth of field for this application. That figure should be treated as a design and setup objective, not a guaranteed capability of every machine or lens.
Focus on the actual upper surface of the secured shim. Do not assume that a warped corner is in the same focal plane as the center. If the sheet is not flat, one part of the pattern may cut cleanly while another part only marks or produces excess dross.
A useful setup sequence is:
-
Secure the blank.
-
Confirm the material surface is flat.
-
Set focus using the machine’s approved procedure.
-
Position the artwork within the flat area.
-
Run the small test pattern.
-
Examine bridge integrity and underside residue.
-
Adjust one process variable at a time.
Avoid making several changes at once. If power, speed, focus, air pressure, and pass count all change together, it becomes difficult to identify why a feature improved or failed.
Clean the cut without damaging bridges
After the disc separates, handle it by the perimeter. Fine bridges can be damaged by aggressive scraping, bending, or twisting. Remove loose residue only with a method appropriate to the material and process, and inspect the disc under magnification if the artwork contains small text or dense linework.
Check for:
-
Fully separated outer edges.
-
Open interior counters.
-
Bridges that remain straight and attached.
-
Slag projecting into the optical opening.
-
Heat discoloration or distortion.
-
A disc that remains flat in its holder.
A small burr may cast a noticeable shadow. If the disc will be used for a recognizable logo, compare a projected test image against the original artwork before making a production batch.
Coated glass gobos use a different process
A coated dichroic glass gobo is not cut like a stainless-steel stencil. The substrate is approximately 1.1 mm borosilicate glass with a dark aluminum or chrome coating. The objective is to remove or ablate the coating while preserving the glass core.
Because the glass remains continuous, internal islands do not need mechanical bridges in the same way as a metal stencil. That allows more detailed tonal or gradient artwork, but the process introduces a different failure mode: cracking or damaging the glass.
Use a laser source and process specifically suited to the coating and glass assembly. The brief identifies 1064 nm fiber and 355 nm UV sources as relevant options, but compatibility and results depend on the exact coating, glass, optical setup, and process parameters.
Before processing, confirm:
-
The disc is identified as borosilicate glass.
-
The coating is suitable for the intended ablation process.
-
The disc is supported evenly.
-
The artwork does not place unnecessary stress near the edge.
-
The selected process removes the coating without excessive heating.
-
Smoke and ablation residue are extracted safely.
Do not treat a coating-ablation result as proof that the same settings will cut through the glass. Cutting the substrate and removing a surface coating are different operations.
Match the substrate to the projector
The substrate must tolerate the projector’s optical and thermal environment. The brief identifies stainless-steel shims as a high-heat option for fixtures rated at 500 W or more, while aluminum foil is described as more vulnerable to warping in high-heat discharge lamps. These are application boundaries, not a universal approval for every fixture or operating condition.
Do not substitute plastic or polymer film for a metal gobo in a high-wattage halogen or discharge fixture. The brief specifically excludes that use because the heat can damage synthetic films.
Where TwoTrees fits
The TwoTrees TS2-40W Laser Engraver is relevant to this workflow only when its exact optical configuration, focus behavior, air-assist setup, and supported process are suitable for the chosen gobo stock. A 40 W rating alone does not establish that every 0.1 mm stainless-steel design will cut cleanly, preserve 0.2 mm bridges, or remain flat.
For a wedding-production shop or event-lighting team, evaluate the complete workflow rather than the headline power:
-
Can the machine hold the thin blank flat?
-
Can the focal setup remain consistent across the artwork?
-
Is air assist directed effectively at the kerf?
-
Can the operator test a representative bridge and letterform?
-
Does the resulting disc fit the intended projector holder?
-
Can the finished gobo survive the fixture’s heat and handling?
TwoTrees’ Official Accessories Collection may help identify related workshop equipment, but accessory fit must be confirmed for the specific machine and process.
Project the test before committing
The final quality check is optical. Install the cleaned disc in the intended gobo projector and project it at the working throw distance. Look for bridge shadows, blocked counters, warped lines, uneven focus, and edge clipping.
If the image fails, diagnose the visible symptom:
-
Melted or missing bridges: reduce localized thermal exposure, review focus, confirm airflow, and reconsider bridge width.
-
Incomplete cuts: check material flatness, focal position, and process compatibility before increasing energy.
-
Heavy underside slag: inspect air-assist direction and heat accumulation in the cut path.
-
Distorted perimeter: improve hold-down and reduce thermal concentration.
-
Cracked glass: stop the process and reassess coating, support, and heat input.
-
Soft or uneven projection: check the disc’s seating, flatness, and projector focus.
A gobo that cuts successfully but projects poorly is not finished. The correct standard is a stable disc with an image that remains legible and intentional in the actual fixture.
