Every 3D-printed project begins with an idea. Where does the idea come from? The simplest solution is to use a model that already exists. Several Internet platforms collect finished 3D models, including MyMiniFactory [1], Thingiverse [2], or even a special NASA [3] website. From these sites, you can download finished 3D models for printing, and in some cases, you can even publish your own 3D models for the community.

Another way to create a 3D model is to scan or photograph real-world objects and then use software, such as a photogrammetry application, to generate a model. For instance, you could photograph an object from different perspectives and from all sides; when you have created 50 or more photos, you can then convert the photos into a 3D model using specialized software. See the 3Dnatives site [4] for an overview of possible software tools, including some open source programs.

A third approach is to design a 3D model directly and then print the design. This article demonstrates this approach with a pair of earrings. Their shape was first sketched the old-fashioned way using a pencil and paper (Figure 1). You can see two rectangles pushed into each other. The next step is to transfer this project idea to a 3D model.

Figure 1: Manual sketch of the planned earring.

Create a 3D Model

Linux supports a number of free programs that can assist with developing a 3D model. For instance, Blender [5] is a good choice that was actually developed to create 3D scenes, render videos, and develop 3D models for computer games. Blender shows its strengths when it comes to organic forms.

But since the earring sketched in Figure 1 is more of a geometric figure, a simpler tool such as SketchUp Free might be more suitable [6]. The browser-based SketchUp is often used in architecture, for example.

From the SketchUp home page, click on Try SketchUp, select the category Personal and, if you haven't already done so, create an account. After that, fill out the form, and you are taken to the page shown in Figure 2.

Figure 2: The SketchUp Free design page.

You will probably not want to print the lady shown in the workspace, so click on the figure and press Delete. Then use the menu in the top left corner below App Settings to specify the units for the project; in my case, I will use millimeters (Regional/Simple Template – Millimeters).

The toolbar on the left side of the screen contains some tools that help you with the construction work. To get the basic shape of the earring (you only need to design one and then print two objects based on the 3D model), click on the rectangle symbol and select Rectangle from the pop-up menu.

Now you can draw a square on the base area. You can specify the desired dimensions of 40x40mm, and the software then adjusts the rectangle accordingly. In the next step, use the Push/Pull tool to raise an area that is 5mm tall out of the rectangle, creating a cuboid (Figure 3).

Figure 3: Lifting an area turns the rectangle into a cuboid.

To create the first shape of the earring, use the ruler tool to create measurement points at the edges of the box 5mm from the corners. Connect the lines using the Lines tool. A smaller rectangle is created on the surface of the box. The Eraser deletes lines that protrude at its corners. The results are shown in Figure 4.

Figure 4: Drawing a helper rectangle on the box.

To obtain the basic shape of the earring, lower the area of the enclosed, smaller rectangle and remove it from the 3D model. This is where the already-familiar Push/Pull tool comes into play. The inner rectangle is pressed in a little bit; you then enter 5mm, and it disappears. Using the principle just described, now create another figure with the external dimensions of 25x25mm. If you now draw a frame around this design with the pointer tool, the software displays all areas of the small figure as dots. The Move tool then moves the small figure to the large one. The result is shown in Figure 5.

Figure 5: The smaller figure is pushed into the larger figure.

The last thing to do now is to integrate the eyelet into the earring using the Rectangle/Circle tool. First you need a center for the circle. Draw two measurement points on the upper corner of the earring using the ruler tool; each of the points needs to be 2.5mm from the edge. Now you can use the Circle tool to draw a circle with a radius of 2mm on the resulting center point in the corner of the design. Afterwards, delete the guides again with the Eraser. The Push/Pull tool then lowers the eyelet as before. This completes the 3D model of the earring (Figure 6).

Figure 6: Lowering and removing the circle.

Next, save the 3D model by clicking on Save at the top and enter Earring as the name. Finally, export the 3D model and select STL as the file format. You can then download the earring.stl file. The 3D model is now available in a form that you can use for further work. Exit the program via Home | Account | Logout.

Slicing the 3D Model

The next step is to generate a file that allows a 3D printer to print the model.

In practice, a quasi-standard has emerged in the form of Ultimaker Cura [7]. Cura is available in versions for Linux, macOS, and Windows. Alternatively, you could use the slicer program that came with your 3D printer. For example, I own a Renkforce RF1000, which includes the Renkforce Repetier-Host slicer program.

After starting Cura, the first step is to configure the printer you are using. Press the second button in the menubar. After you click on the combobox and then on Add Printer, a window appears in which you can select your own printer.

If the model you use does not appear, select a similar one. Since I am printing the earrings on an RF1000 that Cura does not support, I chose the Ultimaker 2+. In the combobox, you have to set the printing material and maybe the diameter of the printing nozzle. In this example, the earrings will to be printed with Polyactic Acid (PLA) filament.

Now you have to make some settings for the profile in the right window. A click on the menu item Show all settings lists all print parameters. Since 3D printers differ greatly, Table 1 shows a few parameters that apply to the RF1000 3D printer used in this article.

Which filament to choose depends on the model and the 3D printer. For printers without headed print beds, only PLA is suitable. For printers with heated print bed, you can choose between different plastics. The height of the individual layers depends on how detailed you want the print results to be. If you select a layer thickness of 0.1mm, you'll create a finer structure.

An infill is the inner structure of the 3D object. Usually, a box structure is printed with a density between 15 and 20 percent. A loose structure inside the object is particularly suitable, because it saves material and makes the model less heavy.

You'll need support structures, or support material, if the 3D printer would otherwise print parts of the object in the air. For this reason, a slicer program automatically generates support structures where they are needed; once the object is complete, you can remove the support structure by pressing it out with your fingers or a modeling tool. (The earrings presented in this article do not have any parts that need to be supported by supporting structures.)

The parameters Print Speed and Travel Speed (of the printhead) will also depend on the 3D printer. You must specify the diameter of the filament separately. The temperature of the extruder depends on the filament. The recommended temperature of the extruder (printhead) is usually stated on the filament packaging. If the 3D printer has a heated print bed, you can adjust its temperature.

If you now load the 3D model you created with SketchUp into the Cura program, you will not see anything at first. The metric specifications of the SketchUp Free and Cura programs do not match. Therefore you have to use the middle mouse button to zoom in on the 3D model, click on it, and then enlarge it. Use the arrows to move the model on the virtual printing bed.

Some tools appear on the left side of the window. If you select Scale and enter 2,000 percent as a factor, the earring will appear on the printing bed. Afterwards, move the earring to the side with the Move tool and load the 3D model a second time – because you want to create two earrings. Again, this model is scaled to 2,000 percent (Figure 7).

Figure 7: Both earrings are scaled and placed on the Cura virtual printing bed.

In a window in the lower right corner, you can see the expected printing time, as well as the required amount and length of the PLA strand. Save to File saves the processing status to the G-code file UM2_earring.gcode, which is used for printing later on.

Click on Preview to see how the 3D printer will print the objects. You can see a collar surrounding the model. The collar is intended to provide more stability during printing and is removed from the objects afterwards. There is also a slider in the middle of the window that you can move to the left. Then you can see how the printhead moves over the objects and slowly creates or removes them.

Before you can start printing, you need to prepare the 3D printer. First, save the G-code file on the SD card for your 3D printer and insert it into the 3D printer.

It is better to choose a 3D printer that has an SD card reader. Otherwise, you have to control the 3D printer from your computer via a USB cable, which has several disadvantages: First, you cannot have full control of the computer during printing, and second, a program abort of the control program would spoil the print. Large, complex objects often require 6 to 10 hours of printing time.

Next, insert a suitable filament spool. It is a good idea to remove the used filament spool from the 3D printer after printing, as the plastic absorbs humidity over time. The material feeder can then no longer transport it correctly. After inserting the filament, let a little extrusion take place so that it is sitting flush in the extruder nozzle.

One useful trick is to paint the printing bed with a Pritt glue pen, even if you have a heatable printing bed. The glue stick has proved its value to this author; after printing, you can wash the glue off easily with a sponge and some cleaning liquid.

Before printing, you'll need to condition the printing bed and the pressure nozzle to the target temperature; wait at least 10 minutes until both are fully heated. A heating coil runs through the print bed. The packaging of the PLA filament used in this example gives 60°C as the printing bed temperature and 230°C as the temperature for the printing nozzle.

Now it's finally time for the actual printing, where the 3D printer automatically unwinds all steps. Those who want to can watch the not-really-exciting process. You should not leave the house in the meantime. Sometimes the object detaches from the printing bed during printing, which requires an immediate stop to prevent possible hardware defects. Keep an eye on the process and check back regularly. While printing, you can see the inside box pattern of the infill created by the slicer program. The blue color in Figure 8 is due to the fact that the interior of my 3D printer is illuminated by two blue LED light strips.

Figure 8: Clearly visible: the box pattern for filling the object.

When printing is complete, you can remove the object from the 3D printer. Heatable printing beds should be allowed to cool down a little at first. The plastic used and the printing bed have different expansion coefficients, so that the object can be easily removed after printing. If it still sticks to the printing bed, a razor blade will help.

You can expect some rework after printing. The first thing to do is to remove the printed collar. A modeling tool has proven to be a good choice for difficult areas. The sharp edges that remain on the objects after removing the collars can be smoothed with a disposable file from the drugstore. Be sure you dispose of all plastic leftovers responsibly.

The budding jewelry designer can also use color to further enhance the earrings. Golden spray paint from a well-stocked hardware store is a good choice. Last but not least, install a ring or hook on each earring so that you can actually attach the earrings to ears (Figure 9).

Figure 9: The finished earrings are ready to wear.

Conclusions

This small example shows the potential of a 3D printer. Once you become accustomed to the equipment and software tools, your options are nearly unlimited, and the results are often impressive. 3D printing is a hobby that continually rewards the user with a feeling of success.