Saturday, January 12, 2019

Relief picture - Part 1

My current project is to create a 3D representation of a watercolor drawing done by one of my grandkids, turning it into a "relief" piece.

This has been rather difficult, but I'm getting there. I'll describe some of the challenges and how I'm solving them.

Color

A rose color is used as an amorphous background, which I am calling an "aura", with disconnected splotches. It also highlights the lettering. I have a pink PET-G which may work. It is translucent, so if I print varying numbers of layers the underlying colors should allow it to vary a bit.

A greenish-turquoise-bluish-teal color is used for a smaller aura and also to color the main subject. There are distinctly lighter and darker areas. I have a green PET-G but as you'll see below it is too bright. I found an interesting PLA color by Proto-Pasta called Mermaid's Tail, which includes mica flakes to make glitter.

It's on a tan or sepia or vellum background. I have a wood-infused PLA that should work nicely.

With 3D printing filament, the color is pretty much constant. I printed some "swatches" to see how increasing numbers of layers would vary the color.

Pink PET-G over black came out quite reddish. Differing adhesion does give a nice variation to the color. We'll see how it works over wood.

I thought the same idea would work for the teal, but it's really opaque.

But the color swatches revealed a different property of the Mermaid's Tail filament. The apparent brightness (lightness) is affected by the orientation of the top layer. Horizontal reflects the most light. Vertical reflects the least, making it darker. Diagonal orientation gives an intermediate color. I wondered if I could use this property by ensuring that the top printed layer of each part of the main subject matched the desired shade.


Digitizing the watercolor

Working from a digital photo, I used Gimp to pull each color area out into its own image. Like many art programs, Gimp has a "magic wand" which enables you to select areas of a specific color or a range of colors. This took a while. I created images for the rose aura, the teal aura, face, hair, upper right arm, lower right arm, left arm, left hand, right hand, the black central part of the lettering, and the rose outline of the lettering. Also one for the black outlines around the main components.

The magic wand pulls in stray bits around the main subjects, and fails to fill in areas solidly. So I used paint tools in Gimp to clean up and fill in. This is perhaps the most tedious part of the process. There's a balance between enough detail and too much detail. I wanted enough to convey the random sense of the auras, and the hand-drawn feeling of the main subject. But too much detail makes a lot of work for Fusion 360, causing it to slow down.

Fusion 360 wants to import images as SVG (vector) files, but Gimp doesn't export SVG. So I used Inkscape to convert each file from a BMP (bitmap) to SVG. Then I imported each into a separate Sketch and extruded each into a Body. I used parametric modeling so I can vary the thickness of each component as I work on the overall relief.

Contours

When I thought the teal would be translucent, I had spent a lot of time trying to figure out how to vary the colors of the main subject by sloping them in a way that made sense with the relief of the main subject. The biggest problem was that lower right arm needed to vary its thickness in the wrong direction, opposite to the direction it should slope visually. Once I realized the orientation affected the light, I adjusted the thickness of each component so the top layer was oriented correctly. (I did this conceptually in Simplify3D software, not by actually printing it.) This looked to be tedious because of needing to keep track of cumulative thicknesses. Fortunately I found in Simplify3D a setting for "External Infill Angle Offsets". I can pick the exact angle of the top layer of each "process". Nice!

That's assuming the top layer orientation is "Rectilinear". There's also a setting for the top layer infill to be "Concentric", which should great for the auras, making their top surfaces more random in color and/or reflection.

This enabled me to vary the thickness of each component of the main subject without worrying about the exact number of layers. Each component (or group of them) could be a "process" in Simplify3D. So the face is lowest. Then the right upper arm and left arm are a bit thicker. Then the right lower arm. Then the hair. Then the hands.

I had hoped to round off the edges of the arms and hands to make it more realistic and organic. But the complex shape confused the Fillet function in Fusion 360, so I had to give up on that idea.

As I stacked up the image layers in Fusion 360 it became apparent that there were some gaps. So I expanded the black outlines into a solid layer (I called the "profile") above the auras and below the body parts. This ensures everything is solid and won't have any unsupported areas. 

Multiple layers

Simplify3D allows you to change parameters as you work your way up through the thickness of a print. Each group of parameters is called a "Process". I organized the information about the components and their thicknesses into an Excel spreadsheet. This let me see for example that the lines-profile and the black part of the lettering go together. The right upper arm and left arm belong together, both from the relief level and color aspect. It worked out to 9 Processes. I need to change filament colors between Processes 1 through 5, and then Processes 5 through 9 are all the teal filament but with different thicknesses and top layer orientations.

In earlier projects I have learned how best to pause a print to switch filaments. Simplify3D allows for "post processing" commands to alter the file it produces. I added commands to pause for the 4 filament changes, and figured out that all those commands need to be defined in the last process. Kind of weird, but it works. I looked at the GCode file to ensure that it was making the changes in all the right places.

Multiple filament types

The first layer will be wood PLA which prints at 210C, then the pink layer is PET-G at 245C, and then the rest are all PLA at 210C. In the first test print I had some problems with the pink over the wood, but I think that was more about retraction/extrusion than about adhesion. I think the pause for the filament switch needs to be tweaked a bit to ensure the new filament starts flowing fast enough.

Test prints

Because the final product will be big, I've tried some small samples.

This first one was 1/4 scale in X and Y, but regular scale in Z (relief) to test out the multiple filaments. There were some problems with the pink not adhering to the wood. The infill was too sparse at 10%, so the upper layers fell through. Because it was at 1/4 scale, the filament could not keep up with some of the fine features and they got gloppy. I'm hoping that when printed at full size those details will work.

The pink and teal auras were thicker than I intended, so I changed them down to one 0.2mm layer. I'm hoping that will make the pink less intense.

For the next test I set the infill to 15% so the upper layers will not have to "bridge". I tweaked some other settings in the infill area. It also seemed that the filament did not start flowing right away after a change, leaving gaps, so I changed the post-change retract from 0.5mm to 0.2mm.

I printed the next test in just one color, at 100% scale, to see if the larger features print better. I went back to Fusion 360 to select a central rectangle instead of printing the whole picture. Here's a shot from an angle to show the relief.

Next I printed the central rectangle with the multiple filaments. Again the PET-G did not stick to the PLA, and vice versa. That caused the black to fail on the lettering, and other problems. So I guess I'll shop for a rose-colored PLA.

The concentric fill in the thin aura layers looks good - the lower pink and teal areas are blotchy like watercolors.

The "canyons" between the body parts, and the black background at the bottom of them, gives good definition.

The varying top layers on the body parts do make them appear lighter and darker, though that does not come through so well in a photo. They shimmer as you move around.

I also remembered that I didn't copy over many of the disconnected blotches of the rose aura, so I'll need to go back to the images and merge them in.