LaserCanvas
Dialling in a new material: the test grid method
Cut a grid of small squares where power varies along one axis and speed along the other, on the actual sheet you are about to use. Read it from the corner that cut cleanly, not the corner that cut at all, then record the machine, lens, air assist and supplier alongside the numbers. This takes about fifteen minutes and replaces every settings chart on the internet.
Why settings charts do not transfer
There is no universal setting for 3 mm plywood. There is a setting for *your* machine, *your* lens, and *this* sheet — and it will change with the next sheet.
The variables that actually move the number are not exotic. Tube or diode output drifts with age and temperature. Lens focal length changes the spot size. Air assist changes effective cutting speed by a large margin. And plywood in particular is not a consistent material: glue lines, void content and moisture vary between batches from the same supplier, let alone between suppliers.
What a test grid is
A grid of small squares — 10 mm is plenty — where one axis varies power and the other varies speed. Each square is cut with its own combination. When it is done, you look at the sheet and pick the square that came out best, and you now have settings for that material.
The whole value is in doing it on the real sheet. A grid cut on an offcut of the same batch tells you the truth; a grid cut six months ago on different stock tells you a story.
Building the grid
- Draw one 10 mm square in the corner of your work area.
- Use the array tool to duplicate it into a grid — five columns by five rows is a good first pass, with 5 mm spacing so the squares do not share heat.
- Assign each column a power: for a first grid, span most of your usable range — say 40%, 55%, 70%, 85%, 100%.
- Assign each row a speed. Start wide, because you are looking for the boundary, not fine-tuning: 5, 10, 15, 20, 25 mm/s on a diode, or 10, 15, 20, 25, 30 mm/s on a small CO2.
- Cut a reference line down one side at a known setting, so you can tell the grid orientation afterwards. Every person who skips this ends up with an unlabelled sheet of squares.
- Run it once, at one pass.
Reading it properly
The temptation is to pick the fastest square that fell out of the sheet. That is the wrong square. It is the setting that *just* cuts, which means it will fail on the next sheet, on a slightly thicker patch, or over a glue void.
- Push each square out from the back. If it needs a knife, it did not cut.
- Discard everything that did not cut cleanly. Then discard the row and column at the boundary too — that is your safety margin.
- From what is left, pick the fastest square with an acceptable edge. Speed is free quality: less heat, less scorching, less time.
- Look at the edge colour, not just whether it separated. A square that cut but is heavily charred is telling you the power is higher than it needs to be.
- Check the back face. A clean front and a scorched back usually means the beam is reflecting off the bed, not that the settings are wrong.
If every square cut, the grid was too timid — rerun it faster. If none did, run it slower or add a pass. A grid where the boundary runs diagonally across the middle is the one that tells you the most.
The same method for engraving
Engraving grids work identically but you are judging contrast and depth rather than separation, and the useful ranges are different — much higher speeds and much lower power. Two changes:
- Fill each square rather than outlining it, so you are looking at a raster result.
- Add line interval as the thing you tune after power and speed. Too coarse and you see banding; too fine and you are just adding time and heat.
On anodised aluminium and coated metals the grid is judging colour change rather than depth, and the usable window is narrow — worth a 5×5 grid with a much tighter range than you would use on wood.
Write down more than the numbers
A setting without its context is nearly worthless six months later. Record, at minimum:
| Record | Why it matters |
|---|---|
| Machine and wattage | The obvious one, and the one people assume is implied |
| Lens focal length | Changes the spot size, and therefore everything |
| Air assist, on or off, and roughly how much | Shifts achievable speed substantially |
| Material, thickness, and supplier | Plywood from two suppliers is two materials |
| Date | Tube output falls off over time; a two-year-old number is a different machine |
| Bed type and whether the work was raised | Explains back-face scorching later |
The date is the field people leave out and later wish they had. It is the difference between "these settings stopped working" and "my tube is three years old".
How often to redo it
- Every new supplier, always.
- Every new batch of plywood, if the last one gave trouble.
- After any optical change — new lens, cleaned mirrors, realignment.
- When a setting that always worked suddenly does not. That is data, not bad luck.
Common questions
How big should the test squares be?
Around 10 mm. Small enough that a 5×5 grid fits in a corner of a scrap sheet, big enough that each square has a real perimeter to judge and does not suffer from the machine decelerating through every corner.
Should I vary power or speed if I can only change one?
Speed. It is the safer variable: raising speed reduces heat input, scorching and cycle time all at once, and most machines have a wider usable speed range than power range. Power near the top of the range also tends to be the least linear part of it.
Why did my settings stop working on the same material?
Most often one of four things: a dirty or shifted lens, a different batch of material, a tube or diode that has aged, or air assist that has quietly weakened. Re-run a small grid — it is faster than guessing, and it tells you which of those it was by how far the boundary moved.
Can I use someone else’s settings as a starting point?
As a starting point for the grid range, yes — that is a good use of them. As a value to cut with directly, no. Use them to centre your grid, then trust the grid.