Laser Perforations

A discussion on the LightBurn forum produced a hacky way to laser-cut pinholes at precise locations:

That’s the 0.3 mm exit wound in 3 mm acrylic, one of the mini-lathe chuck stops, carefully hand-held to align the channel.

Squinting at similar holes through clear acrylic shows they’re smoothly melted (as you’d expect), but not exactly perpendicular to the surface. I’m sure the acrylic gas pushes the beam around and erodes the sides of the channel as it boils out of the progressively deepening hole.

The entry wound is about half a millimeter:

The heat-distorted strip around the perimeter is less obvious in real life without magnification. The protective plastic film over the surface melts easily and, although it does keep the fumes from condensing, causes a bit of damage.

Each pinhole comes from a single dot in LightBurn’s Dot Mode, so you must arrange the dot spacing to match the path:

The pockets are on a 40 mm BCD, so they’re out 20 mm from the center and the hole-to-hole distance is:

34.64 mm = 2 × 20 mm × cos(30°)

Set the dot distance to that exact number and It Just Works.

The laser turns on for a specific number of milliseconds at each dot. In this case, I used 50 ms with the layer set to 70% PWM. You could surely optimize the values.

The starting pinhole gets drilled twice, which happens because Dot Mode expects to make a line of perforations with one dot at each end. In this case, the end of the last line overlaps the start of the first line; two lines would work better than a triangle.

You could make a square array from a single line with (many) dots at the desired spacing, separating the lines by the same spacing.

A circular array might work, too, with a straight line joining successive holes.

Undo would definitely be my copilot while figuring those out.

This could make an easily clogged trash strainer or a filter for small chunks.