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I would share the process that how to make a 3D parts with complex shape.
You may happy with that with this easy way.
For Chinese version: http://regishsu.blogspot.tw/2017/04/easycardrfid-mrt-3d-1.html
The tools and parts list:
1. 3D printer
2. Hot glue gun
3. Key ring chain
4. SketchUp Make version - https://www.sketchup.com/
Step 1: Take Picture With a Reference Lines Background
First, you need find a stuff with square lines for the background.
I am using a grid pad, however, you can use grid paper instead.
Put the part on this grid pad or paper and take a picture.
Step 2: Drawing the Shape With SketchUp
Follow the steps as picture1
1. Import this picture from File->Import
2. draw a rectangle with real size W and H
3. use Resize tool to adjust the size with this rectangle and put together
4. use Line tool to draw the edge of picture
5. remove the rectangle and keep the real shape
6. use Offset tools to enlarge the shape and use Push/Pull tool to make the thick
Step 3: Make the Parts With 3D Printer
Export stl file from SketchUp plugin tool.
Using Cura to slice the layers as G-code and then print it by 3D printer.
My printer is a DIY model - Prusa i3
Step 4: Pre-matching With the Parts
Please do the matching before assembler to make sure the dimension is correct.
Step 5: Assemble the Parts Together
Glue them together by the hot glue gun.
And then use key ring to chain with this 3D parts.