# CS 294-3: RAPID PROTOTYPING Lecture #4 -- Sep. 22, 2000.

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## Discussion of Assignment A#3

• What kind of symmetrical objects did you design ?
• Review of the various symmetry groups.
• Identifying the symmetry of a varyety of physical objects,
e.g., the knots from Assignment A#2;
symmetry of the trefoils and torus knots;
the figure-8 knot.

## Designing for FDM

• Should have clean B-rep with no self-intersections
- - What is the typical meaning when we have self-intersections ?
- - e.g., a figure-8 shaped contour ?
- - when we have nested contours ?
• Boolean Set Operations
- - What does QuickSlice do with it ?
• Thin-Walled Parts
- - Motivation
• Techniques in QuickSlice
The fast-build option
Manual control of the roads on each layer
• Defining solid models of hollow parts
Supports inside the voids
• Handout: "Layered Manufacturing of Thin-Walled Parts"

## Homework Assignment (Clarified !) :

### A#4: Explore special build modes on the FDM machine

1. Make two mitred face panels for a 2-inch cube with different loose fill patterns.
• Start with a mitred solid square panel, outer edge dimensions 2 inches, thickness 0.12 inches, mitring angle (bevel) 45 degree on all 4 edges. (6 such panels will be assembled into a cube).
• Build each layer (a square slice) with 5 contour roads and a loose fill pattern. One should be the standard cross-hatched pattern, and the other one should be a different pattern in which you chose your own parameters in the advanced mode of the road-building menu in QuickSlice.
• Try to actually build these parts on the FDM machine.
2. Now try QuickSlice on a similar part, but this time YOU will specify the geometry of the loosely filled hole, rather than simply letting it be the remainder of the slice after the 5 contour roads have been laid down.
• Modify your solid above by "subtracting" a brick-like volume from its center; this negative volume should have the dimensions 1' by 1" by 0.12" -- and its top and bottom faces should be aligned flush with those of the original panel. Reverse the normals of this solid. At this point you have the description of the part that we would like to build in solid form. Now we take again the brick-like inner volume, but this time with positive normals, and designate it to be a quickly built cross hatched part. In this way you control exactly what volume will be solid and what will be loosely filled.
• Unfortunately, QuickSlice does not see it quite this way -- and it is not quite clear what its own inner mental model of this situation is. Read the last bullet of the QuickSlice Hints
• Experiment with reassigning the inner contour to different layers, changing their geometry slightly (to make it overlap or not overlap -- but avoiding direct coverage, etc ...).
• No need to actually build this part -- we are just trying to understand what QuickSlice does with different combinations of layers in "red" and in "light magenta"
• Take notes of your findings. QuickSlice is now available on the machines in 349 Soda Hall; it is in a folder on the desktop.

If you do your work on the machines in 349, and want to save any files,
you have to click the "Options" button in the "Save As" menu, and uncheck gzip STL file and gzip SSL file.
{The problem is apparrently because gzip is not installed on those computers.}

Bring your parts from #1 to class, as well as a write-up of your findings and what you learned about QuickSlice by trying approaches #1 and #2.

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