1.build a 3D modal in 123D Design. First build a cube on the screen, then use some functions from the tool bar like modify to design your own shape. I used modify to make it empty from 3 sides. And set some of edges as fillet.
2. saved as .stl file, then open this file in netfabb software to have a check, it goes well.
3. open the .stl file in the Cura software, set some qualities in the left area, layer height is 0.2mm, shell thickness is 0.8mm, set retraction enabled, and 0.6mm for the bottom/top thickness, and fill density is 20%. Then we got the time of the printing. Save it as .gcode file in case if you want to re-change.
4. Copy all the .stl files into the SD card, and put it in the 3D printer — Ultimaker2 port, it’s on the middle of the machine’s bottom. Choose the file and press start, finally print.
The video of printing shows here: