What model of laser is it?
For the most part, you don’t need to be modulating anywhere near that high. The spot size of the laser on a 2" lens might be 0.15mm.
Even if you’re really blazing at 400mm/s, the frequency can be as low as about 5KHz before the modulation effects could begin to show up.
Don’t just think of the frequency in KHz- that’s thinking in time. Think of its period as distance. The time period of 5KHz is 0.2milliseconds. When it’s moving at 400mm/s, the spatial period of a PWM cycle is 0.08mm.
A fast-responding RF laser will completely turn off and turn on the beam at 5KHz, but at 400mm/s that period is still only 0.08mm across, about half the width of the spot as it moves.
Now if the PWM was set really slow- a distance of like 3x of spot size at high speed- then you would see the cut start and stop when moving at that high speed. It makes dashes on the paper. But once the PWM period gets narrower than the spot size, the dashes overlap and it all blends into one cut anyways.
And that’s still true if the PWM period is 4%. At 400mm/s, yes it’s only pulsed on for 0.032mm, but when it’s on, the spot size is the same 0.15mm and pulse is still happening every 0.08mm so it will have significant overlap between pulses and should still be a smooth cut.
The performance gets more consistent the lower the PWM is, until it’s so low the cut starts turning into dashes. The point at which that happens depends on the highest speed you’re using. 400mm/s is “pretty darn fast” and most laser cutters won’t even reach that without a cut being several inches long and basically straight.
Set min power to 0%. The machine should basically be linear. The basic (there’s some actual implementation details that make it a bit different than this, but it’s mostly true) way it works is when the controller is accelerating/decelerating on vector cuts and not able to achieve the commanded speed, it will proportionately scale back power between max power and min power. e.g. you set 100% max power and 0% min power, at 400mm/s. It’s making a big rectangle and actually got up to 400mm/s on a side, but now it’s approaching a corner. It’s braking to a stop on the corner, so it will go 300mm/s… 200mm/s… 100mm/s… timed so it will stop at the corner and be 0 mm/s, then goes off the other direction at 100… 200… 300… 400.
At the moments it’s doing 200mm/s even though you asked for 400, if you used 100% max 0% min then it will be scaling power to 50% for you, for that moment. Since it’s taking 2x as long to cover each 0.1mm of the plywood, that always basically delivers the same amount of energy per unit of distance as it slows down/speeds up.
If you asked for 40% max power and 0% min power, it will scale the power to 20% at half speed. Still delivering the same energy per mm.
I see a lot of people who don’t understand min power just set max and min to 100%. So when it starts/stops/corners, it briefly delivers more energy per mm. At the actual corner, where speed is nearly 0, it’s a LOT more. On through cuts, this doesn’t get noticed much. A little wider cut, more flashback from the honeycomb. If you’re trying to vector engrave acrylic and want the line to only go about 1/10th the acrylic’s thickness, setting min power too high will totally make it spike through the full thickness of the material at starts/stops/corners.
