LaserCanvas
Power, speed and passes, and how they trade off
What the material feels is energy per millimetre — roughly power divided by speed. Halving the speed does about what doubling the power does, so many combinations cut the same. Choose between them on edge quality: for cutting, prefer more passes at higher speed over one slow, hot pass.
One number matters, and it is not power
Power sets how much energy arrives per second. Speed sets how long the beam spends over any given point. Neither alone determines the result — their ratio does.
| Power | Speed | Relative energy per mm |
|---|---|---|
| 60% | 600 mm/min | baseline |
| 30% | 300 mm/min | about the same |
| 60% | 300 mm/min | about double |
| 100% | 1000 mm/min | about the same as the baseline, but gentler on the edge |
The last row is the useful one. If two settings deliver the same energy, the faster one usually gives a better edge, because heat has less time to spread sideways into the material.
Which to change, and when
| Problem | Change | Why |
|---|---|---|
| Not cutting through | Add a pass first | Each pass clears debris so the next reaches deeper, without more heat at once |
| Edges charred and wide | Raise speed | Less dwell time, less sideways heating |
| Engrave too faint | Lower speed slightly | Power tends to widen the mark rather than deepen it |
| Engrave blotchy | Lower power | Dots are merging into solid burn |
| Taking far too long | Raise power and speed together | Keeps the ratio, cuts the time |
| Flare-ups | Raise speed, add air assist | Heat is accumulating faster than it disperses |
Why several fast passes beat one slow one
It is counterintuitive — the same total energy, delivered differently — but the difference in the finished edge is large.
- Debris clears between passes. Smoke and ash in the kerf absorb the beam, so a single slow pass is partly cutting through its own waste.
- Heat dissipates between passes. A slow pass builds a hot zone either side of the kerf, which is what the char actually is.
- Flame is less likely. Sustained heat in one place is how a flare becomes a fire.
- It fails more gracefully. Two passes that nearly cut through can be followed by a third. One slow pass that overcooked the edge cannot be undone.
The exception is acrylic, where a single pass gives the polished flame edge and extra passes cloud it. Wood wants multiple passes; acrylic wants one good one.
Minimum and maximum power
Many controllers expose both. They matter when the head slows down — at corners and on small curves, the machine decelerates, and at a fixed power that means more energy per millimetre exactly where you least want it. That is why corners burn darker than straights.
- M4 dynamic power mode on GRBL scales power with speed automatically, which largely solves this. Use it if your controller supports it.
- Minimum power should be just below the material’s marking threshold, so the beam does nothing while the head is crawling.
- If corners are visibly darker than straights and your controller supports M4, that is the first thing to try.
Finding the setting rather than guessing it
- Cut a test grid on the actual sheet: power along one axis, speed along the other.
- Find the swatch that just cuts through cleanly.
- Back off slightly from the extreme — a setting on the edge of working will fail on the next sheet.
- Write it down with the material, the thickness and the date.
Common questions
Should I increase power or decrease speed?
They are close to equivalent for how much energy goes in, so choose on edge quality. Running faster at higher power generally gives a cleaner edge than running slow at lower power, because heat has less time to spread sideways. If you are already at full power, the choice is between slowing down and adding a pass — usually add the pass.
Is it better to use multiple passes or one slow pass?
Multiple passes for cutting. Each pass clears debris so the next reaches deeper, heat dissipates between them, and the edge chars far less. Acrylic is the exception: a single pass gives the polished flame edge and extra passes cloud it.
Why are the corners of my cuts darker than the straight sections?
The head decelerates into corners, so at fixed power more energy lands per millimetre there. GRBL’s M4 dynamic power mode scales power with speed and largely removes it. Setting a sensible minimum power helps too, so the beam does nothing while the head is crawling.
Why do settings from someone else’s machine not work on mine?
Because a setting is one point on a curve that depends on optical power, lens, focus, air assist, the exact sheet and how clean the optics are. Even two machines of the same model differ. Use published settings as a starting point for a test grid, never as an answer.