Challenge Your Students to Create and 3D Print an Intersecting Silhouette
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TETe – INTERSECTING SILHOUETTES intersecting silhouettes CHALLENGE YOUR STUDENTS TO CREATE AND 3D PRINT AN INTERSECTING SILHOUETTE echnology and engineering students meaning to a person who sees the object from are often given challenges to design a particular vantage point using the silhouette and create a prototyping for a product of the object. Silhouettes are filled outlines of that meets a particular need. However, an object without any internal distinguishing Tin process engineering, there may be instances features. They have been used for millennia where students could instead be asked to refine (Jackson, 1911), with applications in historiogra- BY a particular process and find applications for phy, art, design, and signage. A silhouette can it. This article shares a basic procedure for be cut out of paper, steel, or other flat sheets of JIM creating a product that is the intersection of material. As you walk around it to view it edge- FLOWERS silhouettes, and it is especially appropriate for on, the image disappears into a line. technology labs where students can use 3D design software and 3D printers. Now imagine a physical object where you see a silhouette by looking at the front of the object. BACKGROUND But with this object, as you walk around it or rotate the object in your hand, a completely In two-dimensional graphics, the term “ambig- Intersecting different silhouette appears, a 3D ambigram. ram” refers to “a word, art form, or other symbol- silhouettes are Jonathan Borofsky’s 2004 sculpture at Penn ic representation whose elements retain mean- Station in Bal- sometimes ing when viewed or interpreted from a different timore, MD, direction, perspective, or orientation” (Wikipedia, greeted with Male/Female, n.d., Para. 1). Scott Kim (1981) shared many ““Wow” by shows two original ambigrams in his book called Inversions, those who extruded sil- where the title of the book reads as his name houettes that don’t expect a when viewed upside down (Figure 1). are crossed second image (Figure 2). or second set of text to Figure 2. Male/ Female, 2004, appear. Jonathan Borof- sky, Penn Sta- tion, Baltimore, Figure 1. An Ambigram Reading as Inversions and, MD. Retrieved when rotated 180°, as Scott Kim (Kim, 1981, p.4.). from http:// www.borofsky. com/index. In the design of three-dimensional objects, some php?album= products, such as signs, are designed to convey malefemale May/June 2016 technology and engineering teacher 1 TETe – INTERSECTING SILHOUETTES Another example integrity, greater clarity in the ability of the design to communi- of this is the cover cate, or aesthetics. art for Douglas Hofstadter’s (1979, ESSENTIAL PROCEDURE reprinted in 1999) The essential procedure for creating an intersecting silhouette book, Gödel, was demonstrated at an ITEEA conference and took less than Escher, Bach: An one minute (Flowers, 2015). It is illustrated here with an object Eternal Golden that reads “Top” when viewed from the top, but “Front” when Braid (Figure 3). viewed from the front. In this instance, Rhinoceros™ 3D design The “shadow software was used to create the virtual object, and a Stratasys blocks” depicted uPrint™ SE Plus was used to build the resulting physical model. there cast the shadow of a differ- 1. Two silhouettes were created, one in each of two views ent letter in each of (Figure 4). In this instance, a font was selected that allowed three directions. the letters to be moved so they slightly overlapped, but with- Figure 3. Shadow out losing the shape of the letter. Fonts will be discussed in blocks as cover art greater detail below. A text command was used to create (Hofstadter, 1999, solid letters in the top view spelling Top, though these could originally published in 1979). have also been created as lines or surfaces and extruded then capped as solids. Solids for the letters in Front were However, longer lines of text can be used than shown in the created in the front view. 1-letter shadow blocks, and the technique could be used with non-text silhouettes. When created with digital design software, the resulting virtual objects can be rotated to reveal first one view, then a surprising second view, and in rare cases, maybe even a third silhouette. It is also possible to use additive prototyping technology such as 3D printers to build physical models of intersecting silhouettes— Figure 4. Initial extrusions (of Words) in the Top and Front views. at least for those that would have sufficient structural integrity. Subtractive methods from scroll saws to lasers could also be 2. In the top view, all the letters in Top were brought to a com- used to cut first one silhouette out of a block in one orientation, mon baseline if they were not already on it. The letters were and then a second using a second orientation. then moved (horizontally in ortho mode so they only moved in one axis) to create what seems like enough overlap be- This is not to be confused with technologies and algorithms for tween letters to provide for structural integrity of the model, 3D modeling an object based on the information in a series of but not so much as to obscure the letters (Figure 5). silhouettes (Rivers, Durand, & Igarashi, 2010; Liang & Wong, 2010). Instead, it is a tool for designing products that appear to change with one’s vantage point. “A prototype is a working model used to test a design concept by making actual observations and necessary adjustments” (Benchmark 9K from ITEA/ITEEA, 2000/2002/2007, p. 105). With intersecting silhouettes, both the observation of the virtual model prior to building and of the finished model may lead the designer to make refinements regarding font selection, scaling, and other design decisions that could lead to better structural Figure 5. Moving letters so they overlap. 2 technology and engineering teacher May/June 2016 3. A Boolean union was performed on the letters in Top so from the vantage point where they ought to be legible (Fig- they became a single solid. ure 7). 4. In the front view, the letters in Front were brought to a com- 10. Once the virtual model passed inspection, it was exported, mon baseline, overlapped, and unioned. in this case as an .stl file for 3D printing. 5. The lengths of the two objects were compared starting with 11. In the software controlling a 3D printer, the .stl file was a common origin at the left of the object. A decision was loaded, and the object was scaled and oriented as desired. made to scale one or both objects, either 1-dimensionally 3D printing parameters, such as the internal density of the along its length, 2-dimensionally, or 3-dimensionally, so that model, were specified. The software digitally sliced the the final objects had the same length. In this example, only object, created virtual supports, created toolpaths for the slight 1-dimensional scaling was used. extruding head, and sent the object to a 3D printer. 6. The objects were moved so that they intersected in all three 12. The object was built from the bottom layer up (Figure 8). In principal views (Figure 6). this case, the 3D printer laid down spaghetti-like strands of a blue thermoplastic (acrylonitrile butadiene styrene) to cre- ate each layer, with separate white support material used for areas such as overhangs that required support. After each layer the table moved down, and the next layer was built on top of the previous layer. Figure 6. Repositioning unioned and scaled objects so they intersect. 7. A Boolean intersection was performed so that only those volumes in common to both objects are kept. This some- times does not work, with the software reporting a failed attempt. In those instances, slight adjustments could be made to the position of the objects before re-attempting the intersection. 8. The mouse was used to click on the object, realizing that this might not select non-contiguous areas. The selection The object being built in a uPrint SE Plus™ 3D printer. was then moved to show any remaining non-contiguous Figure 8. areas. Those non-contiguous portions were deleted. 13. After building, the object was removed from the 3D printer. In this case, the support material was dissolved in a diluted alkali bath (Figure 9), after which the object was washed, rinsed, and dried. Figure 7. Results of a Boolean Intersection 9. The virtual model was shaded and rotated to look for areas that might be problematic for building or handling, such as very small connective areas between letters or instances where some characters may not be legible when viewed May/June 2016 technology and engineering teacher 3 TETe – INTERSECTING SILHOUETTES manipulated in an attempt to produce a viable model. The big- gest factor, though, is the choice of font face. FONTS There are many issues concerning the design of fonts used for intersecting silhouettes and physical models that result. In the USA, fonts are not covered by U.S. Copyright law and may be edited as needed. Most fonts do not work well in silhouette intersections for products that will be manufactured. Many fonts contain line strokes that are so thin that a resulting build lacks the structural integrity for the product to be handled. An object to promote a book manuscript entitled The Selfish Professor was created Figure 9. Dissolving supports with a font face that had rather narrow line strokes (Figure 11). This seemed adequate in a virtual setting, and the object was 14. During a final inspection, touch-up work with pliers, a knife, successfully built. However, the object soon broke because it did or a file improved the model (Figure 10).