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Laser pulse rise time

Not sure if this is the best section but. . .

I noticed some untidy edges when doing fills with Lightburn and mu mini-gerbil board.

The laser pulse does not start instantly - there is a distinct delay from the command to start the pulse and there being enough energy to affect the material.

My tests consisted of two 10mmx10mm squares cut on light plywood. In each case, the square is outlined with a solid line and then filled with the fill set to 100mm/s, 10% power and 250 lines per inch. I know - mixed units. Overscan of 3.5mm is added to ensure that the head is up to speed as it passes the edge of the square.

(image attached - not sure how to insert it inline)

The left square is done with bidirectional scan and looks OK but the bidirectional scan hides what is happening. The right square has a single direction scan. All the other settings are the same. The actual scan direction is right-to-left.

You can plainly see that there is a gap on the leading edge where the laser is not firing. I measure that gap at about 0.5mm meaning that the laser takes 5ms to get up to cutting power.

Although I can work around this for detailed work, I would like to know if this is common, and, if it is, are the numbers pretty normal? that is, should I expect to see a delay of 5ms or so before the laser gets up to power.

Does anyone know if this is a 'feature' of the laser power supply, the GRBL firmware or the PWM frequency. The frequency, by the way, is at the default 1.5kHz so there are only 7 or 8 cycles of PWM in that gap. I can't test higher frequencies because of a bug in the current MG firmware. And, no, I don't have soft start turned on.


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