The finicky details are the easy part

For someone coming from a woodworking background, 3D engraving by laser is as far opposite from carving as it’s possible to get. Not just the medium — multiple machine passes from a specially-prepared bitmap — but also the understanding of what works well and what doesn’t.

When you’re carving something by hand, more details means more work. Every dot or vein or step is another set of moves with the knife/chisel/gouge/whatever.  Another chance to screw up. Every change in contour from flat to rounded to sharp is a change of tool or technique. Another …

Laser couldn’t care less. Dark area in the bitmap representing your picture? Crank the power up and vaporize more material. Light area? Crank the power down. Start at the bottom left (for my glowforge, at least), move right to the end of the bottom-most line of the picture, return to the left, move up a tiny fraction of an inch and do it again. It’s all just a raster.

In fact, complicated images may look better when laser-engraved than simple ones. When you’re working with a sharp blade, slight variations in your materials don’t generally matter a lot. The cut goes where you tell it. So if you want a smooth flat contour, you just make one. Working with a laser, those same slight variations mean that a little more or a little less material will be blasted away for the same combination of speed and power. Unless you sand or otherwise go over the surface to fix things afterwards, flat surfaces will never quite be flat. (And if you have to hand-finish everything, why did you use the laser?)

More fun yet, the laser itself can induce slight variations in about-to-be-zapped material because heat leaks from the area you’re cutting to the material on either side. So even uniform stuff like acrylic can respond non-uniformly to a 3D engrave. For example, one of my first attempts at a Vermont statehouse (depth map processed from an old model in the Sketchup warehouse).

statehouseengrave1

You can see how the surfaces that should be flat are more than a little bit rough.

 

But an image with a lot more detail and a lot more sharp transitions between shallow and deep comes out looking better, because the signal swamps the noise.

greenmanpic

(this one is based on a Green Man model at Thingiverse.)

Oh, and one other thing. Wood chars. And the deeper you cut with a smallish laser, the more charring. But you can clean that up with one final pass at high speed that takes only a cardstock-thick layer off the engrave. And it’s really cool to watch the surface go line by line from dirty to uniformly clean.

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