Technology

cnchologram_20080312.jpg

I posted earlier this week about abrasion holography, a hologram technique that uses a network of simple arc shaped scratches to encode a visible, 3D hologram into a chunk of plastic. Carl was the first to comment on exactly what was on a number of peoples minds:

This is just crying out for someone to generate complex pictures using CNC.

Like many great ideas, someone has already worked this one out! William Beaty was kind enough to write back with a link:

The scratches need to be be almost perfectly smooth with no jaggies at all. Normal CNC doesn’t work, but a couple months ago Evan at homeshopmachinist.net found that “drag engraving” does reduce the jaggies enough.

The photo above is Evan’s cube, engraved on blackened copper. The top image is what you see in normal diffuse lighting. The bottom is one perspective of the hologram when viewed head-on under a point-source light. Evan writes:

The way this type of hologram is generated is to start with a 2d representation of the subject (the cube in this case). Then an arc is drawn using a point on the visible vertices and edges of the shape. A set of closely spaced points along all visible edges is then used to provide the anchor points for the radii of the arcs. The reason the image isn’t perfect appearing is because of slight inaccuracies in the placement of the arcs (my fault) and some waviness in the copper plate which is only 26 gauge material.

There are a lot of creative possibilities with this one. First person to engrave a HACKS hologram on a copper business card wins a standing ovation.

Synthetic Holograms With a CNC Mill – Link
DIY Hand-Drawn Holograms – Link

1 thought on “CNC hologram

  1. I played around with these quite a bit a few years ago myself.

    The simplest way of understanding how they work is to realize that the specular highlight from the scratch moves back and forth with your point of view. You vary the radius of the scratch to get different motions parallax for different points and voila, an impression of depth. You can even create occlusions by interrupting the scratches so certain points are not visible from some directions.

    So…

    Rather than a scratch, how about using threads in an embroidery? Some kind of shiny monofilament thread would probably work best. You’d also want a very fine “backing” thread to keep the curves precise but not get in the way of the highlight.

    I think this could be implemented nicely with something like the Singer Futura. As with CNC, a computer program could then do all the work of laying out the threads from a description of the points. Bonus points for doing hidden-surface removal… although this would be tricky if you have to tie the thread off. Maybe there is a more clever way to “interrupt” a thread.

    CNC is all very well, but you can’t (normally, unless you are a storm trooper) wear plastic or metal plates to the shopping mall.

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