CNC Gilding for Lower Productivity and Higher Cost

A major aspect of my thesis project is to be able to show a robot scribing and punching decoration on a gilded panel. The robot is to have enough human-like features to be uncannily familiar, but enough mechanical or alien features to be clearly non-human.

A robot arm is one way to design a machine to evoke comparison with the human body. However, robot arms are difficult to engineer and control. I cases where smooth, reproducible motion is required, and a constant, controllable force must be produced, affordable robot arms certainly struggle. Home made arms tend to be too flexible, and exhibit oscillations and stick/slip behaviour. More expensive collaborative/industrial arms are more precise and controllable but generally cost US $25k-100k (source, source 2).

Although it does not have the same human-like layout, a simple X/Y/Z stage such as a plotter, or 3D printer makes a pretty good basis for doing this kind of work. They are inexpensive, fast, repeatable, and fairly rigid.

During the first week of October, I modified a 3D printer to inscribe patterns on a gilded panel. I made a simple polished brass stylus to take the place of the traditional agate stone or steel punch used when decorating gold by hand. This brass stylus screwed in place of the 3D printer’s nozzle.

Next I adapted Inkscape – a free piece of graphic design software often used for cheap plotters and laser cutters to output G Code for my 3D printer. This G Code consists of a series of simple XYZ positions and specifies how to get there – speed, straight or curved path, stylus up or stylus down. I substituted a command that raises and lowers the stylus for the laser cutter command that turns on and off the laser.

With a little bit of manual tweaking, I was able to input a graphic, scan it into vector form, output toolpaths for scribing, and set all this up on the printer. The design I made was a motif of gears and lotus flowers meant to symbolize the union of mechanical and spiritual.

A modified 3D printer inscribes designs on a gilded panel

I had to guess at the amount of interference between the stylus and the panel to produce a deep enough impression on the soft panel. As you can see below, it tore through the gold in many places, revealing the brownish bolle, and broke off some of the white gesso/bolle/gold substrate under the flower. Clearly, controlling the pressure is an important parameter, and this setup does not give precise control. I could see the printer and print platform flexing as the stylus moved, which didn’t help. Furthermore, the panel I used was thin, and had warped by the time I made my design!

The lotus flower cracked the gesso/bolle on the panel

Gears and lotus flower motif – the wreckage after scribing by machine

The results were flawed, but promising. I think that by adding spring-loading to the stylus, I could achieve much better control over the pressure exerted on the panel.

There are lots of X/Y and X/Y/Z machines available (link) (link) (link) some readily modified and others designed to be customized. However, one of the most capable machines may be the Silhouette Curio. Designed as a cutting machine for soft media up to 2mm thickness, it is also capable of stippling (puncturing with a needle) and embossing (leaving an impression with a stylus). I plan to experiment with one of these next.