Laser material test: test grids for the right settings

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Tables with starting values help you get going, but you can only find the values for your machine and your material with a test. A material test is a small grid in which every cell is lasered with different settings. Afterwards you see at a glance which combination fits, and you do not have to guess anew for every project.

Why the test is worth it

Percentage values cannot be transferred between machines. 40 % on a 10 W diode laser is something different from 40 % on a 40 W diode laser or a CO₂ machine with 40 to 55 W. Then there are differences in the material: plywood from two batches can react completely differently, because glue, moisture and wood species vary. A dirty lens or a slightly shifted focus also changes the result.

A test costs a few minutes and an offcut. So the rule is: new material, new batch or new machine means a new test.

The four types of test

Start with the grid of power and speed. The other tests build on it.

Grid of power and speed

The basic principle: on one axis the power rises, on the other the speed. Each cell is a small filled square, usually 5 to 10 mm in size. The values are written at the edge as labels.

Sensible ranges to start with on a diode laser when engraving wood:

• Power: 10 to 100 %, in 5 to 10 steps
• Speed: depending on the machine about 50 to 400 mm/s, in 5 to 10 steps
• Line interval: fixed at 0.1 mm

These values are only a frame. Take the manufacturer’s values for your material as the middle and set the range around them. Pay attention to the unit: many GRBL machines work in mm/min, others in mm/s. The LightBurn documentation explicitly warns that a mixed-up unit can lead to movements that are far too slow and thus to fires.

Material test in LightBurn

LightBurn comes with its own generator. You find it under Laser Tools > Material Test.

1. Insert the material and set the focus.
2. Open the Material Test Generator. According to the documentation, it starts with a grid of 10 x 10 cells.
3. For each axis, choose under Param the value that should change: power, speed, line interval or passes. With fibre lasers, frequency and pulse width are also possible.
4. Enter minimum, maximum and Count for each axis, that is the number of cells.
5. Set the mode: Fill for engraving tests, Line for cutting tests.
6. Leave the labelling on via Enable Text. The text gets its own values so that it stays legible without destroying the material.
7. With Frame you check whether the grid fits on the offcut. Then start.

For the line interval there is the Interval Test under Laser Tools. It engraves squares with different spacings. The documentation suggests 0.08 to 0.16 mm as the range. The best cell is the one in which the lines just touch without overlapping. Optionally, the test fills the squares in a single colour or with a gradient, which is often easier to judge.

The Focus Test also exists, but it needs a motorised Z axis that LightBurn can control. Most open diode lasers do not have that. In that case the ramp further below helps.

Material test in xTool Studio

In xTool Studio, the function is called Material Test Array.

1. Connect the machine so that the test is matched to the right model.
2. Create an element, for example a square, and set the processing type and parameters. The grid adopts these values as a starting point.
3. Select the element, open Applications in the left-hand bar and choose Material Test Array.
4. Enter power for the columns (minimum, maximum, count, spacing) and speed for the rows.
5. Generate it with Done. The grid is grouped. If you want to change individual cells, ungroup it.

xTool points out that with very small grids you should check the labels because they can overlap, and that you should watch the machine during the test.

Cut test

For cuts, a grid of squares is not enough, because you want to know whether the part falls out. Draw small circles or squares of about 10 mm diameter and vary speed and passes. After the run, gently press each part. If it falls out without force, the value fits. Do not take the cell with the largest reserve, but the first one that goes through cleanly. Too much energy widens the kerf and chars the edges. Always run cut tests with air assist if you will later cut with it too.

Focus ramp without a Z axis

Without a motorised Z axis you can check the focus with a sloping strip. Place an offcut so that one end lies flat and the other, for example, 10 mm higher on a block. Set the focus to the middle and laser a straight line along the whole length, with low power and high speed. The thinnest point of the line shows the best distance. Measure it afterwards and compare it with your focus gauge. More on this under Laser focus.

Documenting results

A test is only useful if you can find the values again later.

• On the test piece itself: laser the labelling along with it, and write machine, material, thickness and date on the back in pencil. Keep test pieces, ideally on a pinboard next to the laser.
• In LightBurn: in the Library window you save settings as a material entry with thickness and description. You enter the best cell you found there. The library is a separate file that you can back up and take to another computer.
• In xTool Studio: via Material and Add Material you create your own material and save parameters under it. According to xTool, you can also store a photo of the test grid there. Your own materials can be exported and imported.

Note down not only power and speed but also line interval, passes, air assist on or off and the focus distance. Otherwise the result cannot be repeated.

Saving offcuts and material

For tests you do not need a new board. Offcuts from earlier projects are enough, as long as it is the same material from the same batch. A few tips:

• Keep cells small, 5 mm is enough for most engraving tests.
• Choose the spacing between cells tightly, but so that the heat does not affect neighbouring cells. 2 to 3 mm is a good start.
• Test coarsely first, then finely. A 5 x 5 grid with large steps shows the range, a second grid with small steps the exact value.
• Use both sides: engraving tests on the back of an offcut whose front is already used.

Never leave the laser alone during the test. The slow cells with high power in particular can produce flames. A fire extinguisher belongs within reach.

Continue with: Laser parameters, Laser focus and Laser cutting wood.