Guide

Minimum Bridge Width for Laser Cutting

A bridge is the strip of metal left between two cuts. Make it too narrow for the plate you are cutting, and the panel fails on the machine — warping, melting or dropping pieces — even when the design looked perfect on screen. This guide gives the one rule that prevents it, and how to check any file against it.

What a bridge is

In a pierced panel — a jali screen, a gate insert, a railing — the pattern is held together by the metal that is not cut away. Every strip between two openings is a bridge. Bridges do three jobs: they hold the sheet together while it is being cut, they keep loose pieces attached to the panel, and they give the finished panel its strength when it is lifted, carried, welded into a frame and used for years.

A bridge is measured at its narrowest point, not its average. One thin neck in an otherwise chunky pattern is where the panel will fail.

The rule: at least 2× the plate thickness

The safe minimum is simple:

Minimum bridge width = 2 × plate thickness

So a fine, detailed pattern that works beautifully in 1 mm sheet may be impossible in 3 mm plate — the same drawing needs bridges three times wider. This is why a design must be checked for the plate it will actually be cut from, not once for all materials. The number is also the width after the cut has taken its share — see kerf below.

Why thin bridges fail

Heat. A laser or plasma cut pours heat into a tiny line. In a wide sheet the heat spreads away; in a narrow bridge it has nowhere to go. The strip overheats, its edges melt or burn back, and the bridge ends up even thinner than drawn — or gone.

Warping. A hot, thin strip twists as it cools. On a decorative panel that shows as waves across the pattern and a sheet that will not sit flat in its frame.

Dropping and tipping. As the last side of an opening is cut, a weakly connected piece can fall through the slats or tip up into the path of the cutting head. One collision can cost a nozzle — or the whole sheet.

Handling. The panel still has to survive deburring, grinding, powder-coating and fitting. Bridges that barely survived the cut snap under a wire brush or a careless lift.

Kerf: the cut itself eats metal

No cut is a line of zero width. The beam or plasma stream removes a thin slot of material — that slot is the kerf. It matters for bridges because the kerf is taken from both sides of the strip: a bridge drawn at 6 mm finishes narrower once the two cuts beside it have removed their share. Cut-ready files apply a kerf offset to the cut paths so the finished metal — not just the drawing — keeps the width the rule demands. If a file was drawn without kerf compensation, its real bridges are all thinner than they look on screen.

Floating islands

An island is a piece of metal completely surrounded by cuts — the middle of a letter "O", the centre of a star. Nothing connects it to the sheet, so the moment its outline finishes cutting, it is a loose piece on the table: lost, damaged, or jammed under the head. Every island must be either connected with bridges wide enough to pass the rule, or removed from the design on purpose. Finding islands by eye in a dense jali is nearly impossible; a cut-ready file has them counted — the only acceptable count is zero.

How to check a file before cutting

• Measure the narrowest bridge in the file and compare it with 2× your plate thickness — 4 mm on 2 mm plate, 6 mm on 3 mm.
• Check the bridges at the panel edges too; a design sliced by the sheet edge leaves half-bridges that hold nothing. A solid frame around the panel (KraftDXF uses 30 mm by default) prevents it.
• Count the islands. Zero is the only passing number.
• Confirm kerf compensation is applied, so measured widths are finished widths.
• Read the change report. If the file was repaired to pass these rules, every repair should be listed — nothing silent.

Bridge width questions

More guides: Cut-ready DXF checklist · Preparing a design image · All guides