Project 5: 3D Scanning and Printing

3D scanning and printing are two incredibly powerful practices in personal fabrication. 3D printing, on the one hand, allows to create nearly every object that you can think of. Being able to scan objects and get a virtual copy does not only enable you to recreate the objects but also enables you to enhance or extend the object. Even with broken parts, you can print replacements yourself. Scanning is much faster than modeling the object by yourself when the object is complex.

3D Printing

In this assignment we worked with 3D printers. In the group assignment we tested the limitations of the printers.

Menger Sponge

I wanted to print the Menger sponge that I already designed in the third assignment. I used the Ultimaker 2+ Extended that we have in our lab. I used the program Cura to prepare the model for printing. When I imported the stl file in cura I realized that it wouldn't work, as cura shows faces that can't be printed in red. The problem here is the overhang, which means that the red faces are printed in the air and there is no material under it to support it. So it would just fall down while printing.

The original Menger sponge can't be printed this way

I could just have turned the object in cura, but I wanted to add a stand to it so that it could stay on one corner. So I went back to OpenSCAD and edited a stand into the file and turned it on one corner:

rotate([45,35.264,0]) menger_schwamm(3, 0, 0, 0, 3);
difference() {
    translate([0,0,-2.2]) rotate([0,0,60]) cylinder(1,1,0,true, $fn=3);
    translate([0,0,-1.7]) cube([2,2,1], true);

Now I imported the new object into cura again, sliced it for printing and exported it. Then I started the print and waited for it to finish. As settings for the print I used a layer height of 0.15mm and an infill of 18%. I printed the model without support but a build plate adhesion. As the model consists of really small structures the infill doesn't really have any change, because the walls are so near together.

On the finished model, you can see a bit of stringing and blobs. I cleaned it up by hand for this model, using a razor. But the linked website also brings up reasons why these effects happened and how to avoid them for the next print.

The printed Menger sponge

I tried to print it again to get better results. Unfortunately I can't use support material, because the small holes are too small to get it out. I tried another print and used the prusa i3 mk2 this time, because I got better results with it previously. I set the layer height to the smallest value possible, in the hope that I would get a more precise print, but it was just worse. So the settings this time was 0.06mm layer height, 20% infill and no support and no adhesion to the build plate.

The printed Menger sponge with a smaller layer height

The next thing I tried was to put the Menger cube on the side to print it laying flat on one side. Now I printed support material which was touching the ground plate. I used the Prusa again and set the layer height to the normal 0.15mm again. Also I set an infill of 100% to get a more rigid structure.

The cube as it was printed

And standing

With this one am quite happy now, it worked out pretty good. But it is still not perfect, so I guess this model is just too hard due to the huge amount of very small holes in it. One possibility would be to print the model in a printer with two print heads and to use support material which dissolves in water. Another reason I am not trying to get this perfect is that I printed a lot of other stuff, which turned out great. Like the winch shown below. So I guess it is really the model which is hard for printing.

The printed winch which working out really good

The Menger sponge with stand is very hard (if not impossible) to be made subtractively. To get this model you would need more than three axes on the machine because the holes in the cube cannot be drilled from the top but must be drilled at an angle. Even if we consider only the cube without a stand you would need to drill holes from three sides into the object. Trying to turn the object onto one side after drilling the first side would come with small displacements so that the small holes would not hit each other anymore. And even if that would be possible the holes are very small and long with sharp edges. This is hard for a cnc mill and due to the thick material it is also hard for a laser cutter.

3D Scanning

We also had the opportunity to use a 3D scanner. We used an Artec Eva, which is a handheld 3D scanner. This has the advantage that you are not limited to any size or shape of an object because you can just go around as you like. The disadvantage of this scanner is that it is made to scan an object from a distance of half a meter. The object should be at least this size to get a really good scan. This scanner also needs to be wired up to a laptop with the software and power, so you need to move around carefully.

The 3D scanner

The software we used for scanning is Artec Studio. You have a few options for scanning: First, you can decide if you want to scan only the object or also texture. Then you can use a real-time fusion, where the object is rendered on the laptop while you scan it. This is helpful because you can see where parts are still missing. You can also set the scanning fps.

The options in the software

The button to start scanning

It is good to know that you need a base for the scanner to work. So you need to put your object on a flat surface, so the scanner can recognize this as the ground plate. You can start the scanning by pressing the button on the 3D scanner. In the next image, you can see the real-time fusion working pretty well. A few notes for scanning: The LED's on the scanner are blinking fast, which is important to know for scanning persons for example. You should be in distance of half a meter, which is shown in the software on the green bar. The points recognized are shown with the peak and you should be in the middle field for distance. If you turn the scanner too fast or somewhere where no points are it loses orientation and you need to go back to the point where it recognizes the object again.

Live fusion while scanning (different object than mine)

As my object was too small to be scanned I took a plant. I put a small origami crane on the plant. And I would generally say this is a very good object to test the capabilities of the scanner for really difficult objects.

Live fusion while scanning (different object than mine)

As the object was too difficult I did not turn on real-time fusion, so I got a point cloud to work with. As you can see on the right the scanner created 4 different scans because it thought it would be 4 different objects.

Scanning without live fusion

As the program crashes sometimes it is important to save your progress after each step. After executing the global registration under Tools This was the result, which is at least no point cloud anymore. The next point was to get rid of the ground plate, which was also scanned. This can be done in the Editor.

After global registration

After we got rid of the ground plate we did a fast fusion (under Tools again). As the leaves have a lot of detail this was the better option than the smooth or sharp fusion, which would try to do strange things to the details. Also, it is faster with this lot of information. The fast fusion merged the information from the 4 different scans pretty well. Then we did a mesh simplification because the mesh had too many triangles and was huge.

After ground plate removal, fusion and simplification

After the export, I was still left with a 50MB huge 3D model and texture with 500,000 triangles. So I decided to simplify the object further. Therefore I used Autodesk Maya, as I have worked before with it and know that it is able to handle complex objects pretty well. After opening the model I saw that the details were pretty impressive. There is no detail in the middle of the plant and the leaves are hanging in the air, but the details from the parts which were scanned are nice.

The 3D model of the plant

But there are way too many triangles, the mesh is incredible fine as you can see. With this, it is also possible to see the small Origami crane on one leaf, which is really nice. But at the same time, you can see that the leaves themselves are nice, but the edges are really messed up. There are a lot of triangles around the edges which make the plant look frayed.

The mesh of the model

Detail of the plant

I tried to reduce the object to a number of 10,000 triangles, but it just went down to around 20,000 triangles and even then looked awful. The leaves look cornered. If you zoom in you can see the problem: The edge around the leaves still has the most triangles while the big surface of the leaves only has a few triangles. This problem can be solved by removing the triangles by hand, but that is a very long and annoying job and as I don't need the model for anything I didn't do it.

The plant with 20,000 triangles

Detail of the plant with 20,000 triangles

To reduce the size I finally settled for 40,000 triangles, which still looks nice, but is only 10MB big. I also reduced the texture in size by halving the resolution and saving it as a jpg file.

The 3D model of the plant you can download (40,000 triangles)

Unfortunately, the model is too big to put it on the website for interactive exploration, so you need to download it to play around with it.


Here you can download the files created during this week:
The Menger with stand scad file
The Menger with stand stl file in an archive

The archive with the scanned plant (obj format)