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Laser mechanics test
Circles and crosses at several speeds show what a material test cannot: loose belts, backlash, an oval axis, wobble at speed, a gantry out of square. Burn it once, click what you see on the drawing, and get the possible causes, the next check and the fix. Then burn it again and compare.
What you burn: one column per speed, slow on the left. Each column has two circles and a cross through their centre; the outer line is a frame to measure.
- Focus first (see the focus test), and put the scrap flat on the bed.
- LightBurn: File › Open (not Import). Every column already has its speed and power. Before you start, turn off Hide Backlash (Optimization settings) and Overcut, or the test cannot show what they hide. Check Preview, run Frame, then start. Keep your hands off the machine and the material while it runs.
- For a second test, keep the same settings and the same place on the bed, so the two burns compare.
- SVG carries shapes only. In your laser software set every colour to Line / Score with the speed and power from the table.
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Read your test
- Look at the burned test under good light, with a magnifier or your phone camera zoomed in.
- Find what looks wrong on the drawing below: each number marks where that problem shows. Click it to see the cause and the fix.
- Then mark each column, and measure the frame.
What do you see?
Click a number or a line; click it again to clear it.
What each column shows
Speeds are the speeds set in the file. Click a picked mark again to clear it.
Measure the frame
Should be –. Calipers work best.
How it works
- Choose your laser and the fastest speed you use. Download the LightBurn file and burn it on a flat scrap.
- Each column is the same drawing at a higher speed: two circles and a cross through their centre. A healthy machine draws them round, closed and centred at every speed.
- Click what looks wrong on the drawing to get the cause and the fix, pick the fastest clean column, and measure the frame for size and squareness.
Tips
- Run it after any change: new belts, a move, a crash, a new laser module. Keep the scrap: the next test shows whether it got better.
- Where the cross meets the circle is where an axis changes direction. Flats or steps there mean play (backlash) in that axis.
- Only the fast columns bad? That is speed or acceleration, not a broken machine. Cut detail at or below the fastest clean column.
- Do things in order: focus, then the mechanics, then the material test and the kerf test.
FAQ
What does this test check?
How accurately the machine moves: belts, pulleys and wheels (backlash), steps per mm (an oval circle or a wrong size), vibration at speed, and whether the gantry is square. It does not check power or material settings: for those use the material test.
Why circles and a cross?
A circle makes both axes change direction four times, exactly where the cross meets it. Any play shows there as a flat spot, a step or an off-centre cross. A circle that does not close shows where the laser started and finished.
Why several speeds?
Some problems only appear when the head moves fast: wavy outlines, circles that do not close, lost steps. The columns you mark clean show which commanded speeds gave clean shapes on your machine; the head may not reach the full speed on small circles.
How do I measure the frame?
With calipers, from the same edge of each line (left edge to left edge), so the line width cancels out. Width and height show the size accuracy of each axis; the two diagonals show whether the gantry is square. Results are judged against the tolerance you set.
Does a clean column mean the machine really ran at that speed?
Not exactly. The speed in the file is the commanded speed. On small circles the head may never reach it, because acceleration and the controller limit it. A clean column means these shapes came out clean at that setting.
Steps per mm or step length?
GRBL controllers store steps per mm: if an axis comes out too short, the value goes up. Ruida and similar DSP controllers store a step length: if an axis comes out too short, the value goes down. Choose your controller in Advanced settings and the frame check uses the right one.
Does it work with xTool Creative Space or Glowforge?
Yes. The SVG has one colour per column and one for the frame; set each colour to Line / Score with the speed and power from the table. Circles stay real circles in the SVG.
mm/s or mm/min?
LightBurn shows either, depending on your settings. Many diode lasers use mm/min. Pick the same units in Advanced settings. 1 mm/s = 60 mm/min.
Inches or millimetres?
Switch mm / in next to "Test". It changes the circle size, the frame and the labels you see and burn. Speeds stay in mm/s or mm/min, like in LightBurn.