Guide
What Is Bridging in Laser Cutting? (Floating Islands Explained)
By Amir Baker, founder of StencilCut · Updated
A laser-cut bridge is a strip of retained material that connects an otherwise separate part to the rest of a design. It can hold the centre of a stencil letter or join an eye to a cut-out portrait. First decide which regions you are keeping: black artwork and the sheet around a stencil opening need different connections. Then check the exported geometry at its final physical size, not just the preview.
Auto-bridge an SVGChoose what stays and what is waste
For a spray stencil, the sheet stays and the letter-shaped openings are removed. The centre of an O must connect across that opening to the surrounding sheet. For a cut-out black portrait, the black shapes stay and white openings are waste: an isolated black eye needs a black connection, but a white highlight can be a valid hole. Do not fill every white opening just because it is enclosed. A screen colour is not a cut instruction; confirm your retained regions and cut paths in the laser software.
Permanent design bridges versus temporary holding tabs
A permanent bridge changes the shape of the finished artwork and remains after cutting. A holding tab is a short part of a toolpath that is skipped, or partially cut, to hold a piece in the stock until removal. LightBurn supports this second operation through its tabs controls. A tab setting in a laser project is not the same as a connector drawn into an SVG, so confirm what survives when you export or open the file in another program.
Size comes before bridge width
There is no bridge width that is safe for every wood, steel, thickness, and machine. Resizing a drawing also resizes its bridges: a 2 mm connector in a 200 mm-wide design becomes 1 mm when the design is reduced to 100 mm. This is a scaling example, not a recommended minimum. Decide the final dimensions first, measure the narrowest connectors, then check the actual material and cutting setup with the fabricator. Laser power alone does not determine the required width.
Place connections without covering the face
For an elongated detail such as an eye, separated supports on opposite sides can preserve more white space than two stacked bars leaving the same side. Try to follow existing contours or shadows and keep left/right features visually balanced. A centred disc inside a surrounding ring can use three evenly spaced spokes. These are layout options, not strength guarantees: avoid forcing a long line across an open cheek or filling a small feature into a black block just to lower an island count.
Check kerf and the final exported paths
Kerf is the width of material removed by a cut. Closely spaced cuts can leave less material than the drawing suggests. Measure kerf for the chosen stock and setup, then inspect the final paths after any offset or resizing in the laser software. LightBurn documents a test for measuring kerf and applying an offset. Duplicate paths, open contours, and connectors that only touch at a point need inspection too. A sharp preview alone cannot prove those paths are suitable.
What StencilCut checks, and what it cannot certify
The Auto-Bridge SVG tool offers Classic, Photo/Drawing, Text, and Text + Photo modes. Choose the mode that matches the artwork and inspect the result before exporting. Generation uses a separate bridge pipeline; a zero-island result describes the connectivity measured by that pipeline, not a load test or a promise of two strong supports on every detail. Raster resolution and vector tracing can affect small features. Keep the original, compare the bridged version, and manually repair results that damage recognizable details.
A practical pre-cut review
Open the exported SVG or DXF in your laser software and confirm its dimensions. Identify retained material, inspect every isolated region and narrow neck, and check that holes remain intentional. Preview the cut paths and remove accidental duplicate cuts. Ask the fabricator to review the chosen material, thickness, kerf, and handling needs. Test a representative detailed area on suitable scrap using the machine manufacturer's safety procedure before committing the full sheet. If it breaks or distorts, revise the geometry or size and test again.
Further reading
Try it yourself
Compare bridge modes on your SVG, then inspect the exported paths before cutting.
Auto-bridge an SVGFrequently asked questions
Does every enclosed white area need a bridge?
No. If black is the retained artwork, a white area can be an intentional cutout. If you are keeping the sheet around a stencil opening, a centre trapped inside that opening needs a connection to the sheet. Decide which material stays before modifying the design.
How wide should a bridge be?
Choose it for the final dimensions, material, thickness, kerf, and handling requirements. There is no universal safe width. Have the fabricator review the narrowest connector and test the detail on scrap.
Does zero floating islands mean ready to cut?
It means the checked geometry is connected at the resolution used. It does not prove adequate connector width, two independent supports, correct units, or physical strength. Inspect the exported paths at their final size.
Can I use automatic bridges for engraving?
Tonal engraving does not normally need all dark marks connected because the base material remains underneath. Apply connectivity checks to any through-cut parts or outline, not automatically to every shaded engraving detail.
Will the same SVG work on a small laser and an industrial machine?
The geometry can be transferred if the software supports the format, but units, final size, cut settings, kerf, and material suitability still need checking for each setup. A machine brand or power rating is not a bridge-strength specification.
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