LightBurn Overscan, Scan Offset, and Camera Alignment
Three LightBurn tools get blamed for each other: overscan, scan offset, and camera alignment. They all affect how a job lands on the material, but they fix different problems. Once you know which one you are looking at, the adjustment is usually straightforward. In LightBurn's menus these are Overscanning (in the Cut Settings Editor on GCode machines) and Scanning Offset Adjustment (in Device Settings).
If you are seeing doubled lines more than a smeared edge, start with the mechanical checks in Ghosting and Double Lines in Laser Engraving, then come back here for the software side.
What Overscan Does in LightBurn
When LightBurn fills a shape, the head has to travel back and forth. At the start of each line, the gantry is still coming up to speed. At the end, it is slowing down. If the laser is firing during that acceleration, the edge of the fill can look darker, lighter, or slightly stretched.
Overscan adds a little extra travel past the edge of the shape so the head is already at a steady speed when the beam turns on, and still at speed when it turns off. On GCode-based machines, enable Overscanning in the Cut Settings Editor for the Fill or Image layer. That adds extra travel past the edge, with the beam off, so the head is already at a steady speed when it starts burning. The overscan distance is a percentage of speed, and the head needs room on both sides. On DSP controllers such as Ruida, which are common on OMTECH CO2 machines, LightBurn does not show this switch because the controller already handles overscan automatically. If a DSP job reports "Not Enough Extend Space," reduce speed or move the art inward.
If the interior of a fill looks fine but the left and right edges look heavy or smeared, overscan is the first thing we check. On a GCode machine, more Overscanning can help a fast fill, but the head needs room to travel past the art. On a DSP machine, that switch will not be there; if the controller reports it does not have enough extend space, slow down or move the design inward.
Overscan will not fix a fill that is pale in one corner because the bed is unlevel, and it will not fix a zipper edge from bidirectional scanning. Those are different issues.
Fixing Shifted Fills with Scan Offset
Scan offset is for a regular, even mismatch between passes that go left and passes that go right. The fill looks like a zipper, or the edge of a letter has a tiny step on every other line. The machine is firing both ways, which is faster, but one direction is landing a little late or a little early.
That correction is Scanning Offset Adjustment, in Device Settings → Basic Settings. LightBurn can store different values at different speeds, which matters: an offset you found on a slow, dark fill may not be right for a fast, light fill. Engrave a small filled rectangle at the speed you care about (LightBurn's guide uses 50 mm by 10 mm with a wide line interval, such as 0.5 mm). Measure the distance between the mismatched line ends, enter half that distance for that speed, and enable Scanning Offset Adjustment. Run it again and stop when the zipper disappears. Then save the values. If you later change a library preset's speed in a big way, recheck the offset.
If the zipper is huge, or it changes from one side of the bed to the other, go back to belts, pulleys, and head play before you bury the problem in a large offset number. Software can hide a little timing error. It should not be used to hide a loose pulley.
LightBurn Camera Alignment Basics
A camera is a positioning aid. It lets you see the material on the bed, overlay the artwork, and nudge a design onto a bag tag, an ornament blank, or a leftover scrap. It is not a substitute for a square fixture or a good origin, and it is only as accurate as its alignment.
A camera needs two separate setups. First, calibrate the lens, which is usually a one-time step and may use a printed or displayed pattern. Then run camera alignment, which is different: LightBurn burns a target pattern on material in the machine, you capture it, and you tag the targets. Do not print a pattern and lay it on the bed for alignment. Leave the burned targets exactly where they were engraved. In current LightBurn, open the Camera Alignment Wizard from the Alignment button in the Cameras / Overlays window, or from Align to Workspace in the Edit Camera window. Do the alignment at the same working height you will use for real jobs when the process asks for that. A camera aligned at one height can be off at another, especially on a wide bed.
After alignment, do a real check: place a scrap, position a small shape with the overlay, run it, and see if the engrave matches the preview. If it is consistently off by the same amount, realign rather than guessing on every job. If it is close in the center and worse at the edges, that is common with some camera setups. Use the camera for placement, then verify critical work with a fixture or a light test mark when the tolerance is tight.
When Camera Alignment Goes Wrong
The usual causes are simple. The camera moved. The lens or window is smudged. The lighting in the cabinet changed, so the overlay is hard to read. Someone ran the alignment at a different height. Or the material is thicker than the last job, and the overlay no longer matches the surface you are about to burn.
Clean the camera window, confirm the mount is tight, and rerun alignment if the camera or the machine has been moved. Do not keep "fudging" a bad overlay for a week of production. That is how a whole batch of parts ends up a quarter inch off.
A camera overlay that looks wrong can also make you think the machine is ghosting when the finished engrave is actually sharp. Trust a test mark on the material more than the picture on the screen.
A Practical Setup Order
When we set up a machine or chase a placement issue, we use this order:
Make sure the bed is level and focus is set on the real material.
On a GCode machine, confirm Overscanning is enabled for the Fill or Image layer. On a Ruida or other DSP controller, skip this switch; the controller handles it, and a "Not Enough Extend Space" error means you need more room or a slower speed.
If Bi-directional Fill edges look zipper-edged, run Scanning Offset Adjustment at that speed and enter half the measured gap.
Calibrate the camera lens if needed, then run camera alignment with laser-burned targets, and verify with a small test shape, not a full production file.
Save the working settings and only then load the real job.
Overscan, scan offset, and camera alignment are not mysterious once you separate them. One cleans up fill edges, one lines up bidirectional scans, and one helps you place the art. Used together, they make LightBurn feel a lot more precise, especially on the kind of one-off and short-run work we do every day.
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