Assignments Goals

• Test the design rules for your printer(s) (group project)
• Design and 3D print an object (small, few cm) that could not be made subtractively
• 3D scan an object (and optionally print it)

Week's Lectures

3D Printing Design Rules

The first step in this week assignment was to test the design rules for the printers in our FabLab. There we have a Ultimaker Original, a Arduino Materia 101, and other printers that at the moment are unavailable.

To test the possibilities, and the design rules, we designed a simple mechanic part, with holes, bolt housing, overhangs and inner windows, so to stress some of the critical constraints on our printers. Then we printed the object in PLA with both the Materia and the Ultimaker, using Cura as slicing and g-code generation software.

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The result with the Ultimaker was quite good, in respect to the original CAD design, but not perfect: The holes were not perfectly circular and the overhang at 60° had some problems. The overall was anyhow acceptable.

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The result with the Materia, for some particulars, was better than the Ultimaker: the holes were almost perfectly circular and the overhang at 45° was quite regular. The overhang at 60° instead was worse than the Ultimaker one. The overall was anyhow quite good for a mechanical part, with some degrees of tolerance.

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As second experiment, we decided to print the 3D Printer Tolerance Object that Neil posted on Thingiverse. It is a quite complex object with a lot of particulars.

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The result with the Ultimaker was quite awful! There were a lot of stringy filament residue, the text on one vertical wall was almost illegible, the top circular rings were not created, the pointy object was very fragile. Some of these errors were due to bad settings of the slicer program, and others were due to some problem in precision with the machine itself (the moving rods where not really clean).

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The result with the Materia was considerably better:

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In conclusion, every printer has its quirks, and every object is different. So the best way to obtain a good print, it to tweak the print parameters (such as layer height, travel and deposition speed, infill and outer shell) accordingly to the object geometry and structure, having in mind possible limits due to the intrisic precision of the machine.

In a lot of cases it's a good practice to place the object in a way that simplify the print process (i.e. to avoid steep overhangs, or to avoid the usage of supports).

Work files links

Additive Design

The second assigment for this week is to design and print a small object, that cannot be made by subtractive process (for example by milling a solid block of material).

I decided to try to design a simple object with another free object inside of it. I created my design using SketchUp, with a couple of useful plugins: STL Exporter, and Solid Tools. The first is used to export your design in STL format, the second is used to check the model for errors, and to easily fix them.

So I started creating a triangle with rounded corners, to use as a path to revolve another triangle. In this way I created a hollow tunnel in a triangular shape. Then, using the section tool, I created a small sphere inside the tunnel.

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This kind of object it's impossible to generate in a subtractive way, because there's no way to create the inside object without milling into the external hull. Moreover it's almost impossible to create a completely closed but hollow object with subtractive process.

When I was happy with the dimensions and the overall design of my object I exported it in STL format and printed it with my own FlashForge Dreamer, using PLA filament and default parameters:

• Layer height: 0.2 mm
• Speed: 80mm/s

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When the small sphere was completely generated, I detached simply by pushing it with a screwdriver. When the object was completely printed, the sphere was free to move inside the hollow of the object!
Nice ;)

After that, I wanted to try to design and print something more complex, so I came up with the idea of a cocktail glass with an integrated straw running all along the glass surface.

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At the beginning was quite daunting, because I couldn't extrude a circle along a helix path. Then after a couple tutorial on YouTube I managed to create the twisted straw and completed my obect design.

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The print result was acceptable but not outstanding. There were a couple holes between the spires of the straw, and helix walls were too thin. Anyway it's a cool object to view!

Work files links

3D Scanning

The third assignment for this week was to scan something andcreate a 3D model of it, and eventually 3D print the result. I decided to use a Kinect for XBox 360 with a free software called Skanect.

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A collegue of mine was kind enough to act as a guinea pig. So to have a solid and simple setup, I positioned the Kinect on a table and used a swivel chair to rotate almost constantly my collegue on top of it.

Then I started the process on the Skinect software and slowly rotated the chair. After that I ended up with an almost full scan of my friend. To adjust the model, and to eliminate unwanted parts, I filled holes (there was a big hole in my friend's head) and I cropped to lower part of the body.

Finally I applied the textures to the model, and exported in STL.

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To check the result and make a render of the model, I imported it in Rhino, with default settings.

Work files links

Assignments Outcomes

• Identify the advantages and limitations of 3D printing and scanning technology
• Apply design methods and production processes to show your understanding

Have you:

described what you learned by testing the 3D printers
shown how you designed and made your object and explained why it could not be made subtractively
scanned an object
outlined problems and how you fixed them
included your design files and ‘hero shot’ photos of the scan and the final object