I had been quite successful doing single depth of cut engraving for some time now. Now I was looking for new capabilities. I had previously cut some 2.5D graphics on wood or phenolic boards. It was during one of these milling sessions that I found that my movable gantry cnc machine was not precise enough. Round objects turned out to be ellipse shaped when the milling was completed.
After many attempts at rectifying the problems and gradually making improvements, the movable gantry cnc machine was able to give quite satisfying results. So I was ready to try 2.5D engraving again, this time with the intention of making acrylic side lamps.
As I did not have any acrylic sheet with me then, my first attempt at milling a 2.5D image was done using a transparent piece of CD. This was actually my experiment with using the image-to-gcode feature in LinuxCNC, trying to figure out what the settings should be and how to get them right.
I found the result of the milling of a galloping horse was surprisingly good although the engraving was extremely small. It had to be small in order to fit into the space available in the transparent polycarbonate CD. Then I tried to do the same 2.5D engraving of a galloping horse on a slightly larger piece of transparent plastic to try out how to generate a larger image g-code. This time, the acrylic that I had available was in the form of the cover of a CD box. Again, I was able to experiment with the settings available and learned from the exercise.
Finally I was ready to attempt the cutting on a real piece of acrylic sheet. I bought a piece of 2mm thick casted acrylic for this purpose. Naturally, my image would be enlarged to fit the size of the acrylic. I tried out the gcode generation on LinuxCNC and I cut the 2.5D image using a 60 degree conical bit. With this bit, the image consisted of many closely spaced lines.
Later, I bought a round end mill bit and the lines tend to merge better resulting in a better image.
Encouraged by the good results of the galloping horse image, I decided to do another 2.5D image, this time a Dragon and Phoenix image on a larger piece of acrylic. The results were very good.