Recently, I came across some techniques for stippling pictures which were suitable for cnc milling. The strippling technique was ideal for the pen plotter, but since I had already installed a milling spindle for cutting, I thought it would be a good idea for me to try it out with some shallow surface engraving.

full length photo

Full length photo

Prior to that, I had already prepared a few pieces of masonite boards by coating their top surfaces with white paint. By engraving on them, the natural colour of the masonite board would show up as lines or dots against the white paint background.

Preparing potrait using GIMP software

Preparing potrait using GIMP software

First, I needed a suitable photograph. I chose one of my son’s photograph for my experimentation, because his birthday was approaching fast, and I wanted to master the technique so that I am able to give him a special stippling engraving for a present by then.

cropped potrait with background removed

cropped potrait with background removed

As an artist, I knew that there must be a central subject in order to create interest. So I did some cropping and erasing of the background using an open source image editor called GIMP.

Next, I used another software called stipplegen which helped me to create TSP or travelling salesman problem paths. I had to experiment a bit in order to find suitable densities for the paths.

If I selected too few paths the features of the image would become unrecognizable. However, if I selected too much, the regeneration time would be extremely long. The computer itself would hang and become unresponsive. The g-code files would also become extremely large, and the programs would also stop working or experience time out due to the long waiting time.

Creating dots took much longer than TSP, so I decided to use the latter technique in my first attempt.

Potrait on tsp (travelling salesman problem)

Potrait on tsp (travelling salesman problem)

Well, the g-code generated worked well, and I got the movable bed cnc machine to respond to the commands. But what I found was that the picture created by milling was slightly faulty. Some parts were not showing! The movable bed was not fully level. Previously for other projects, this was not a problem because some slight differences in depth of cut would not be noticeable. (We are talking about differences of between 0.1 to 0.2 mm here)

Because the whole picture was cut to the same depth, it was quite noticeable this time. So I decided to do a complete facing operation of the movable bed.

Luckily, the g-code for facing was readily available on the internet, and I did not have to do much calculation and tweaking of the codes. Once the milling tool had completed the zig-zag movement over the entire movable bed, I was ready to try my hand again at stippling engraving.

Leveled movable bed

Leveled movable bed. There were some previous marks which was cut deeper. All the square lines were no more.

This time, I had some time to do a stippling dot operation. The engraving was quite nice, but it took a long time.

Stippling dot portrait

Stippling dot portrait after movable bed leveling.