Optimization for support structures
- Crossbow Body
The body of the crossbow will be printed on it’s side so that the only support material that will be required, is in the tracks where the pencil will sit. Minimal support will be required here in comparison to the amount required if it were to be printed right side up. If it were printed right side up, the underside body cavity would require an excessive amount of material and extra build time. In addition, a sideways orientation will eliminate any need for support material within the pin holes.
- Bow
The bow will sit on the build platform in the same orientation that it would sit if the bow were about to be fired (right side up). In this orientation, nearly zero support material would be required with the exception of the holes that are used to lace the drawstring. Other orientations, such as a smiley face (90 degree rotation about the x-axis) or frowny face (270 degree rotation about the x-axis) would generate a significant need for support materials.
- Other Components
All remaining components are small enough that build orientation is largely irrelevant. An example of this is the crank assembly which has no obvious orientation.
Infill Percentage (Build Time, Part Strength)
- Build Time
The parts build time is outlined in Table 1 below. Total time per part will be highly dependent on both the infill percentage and amount of support material. The part orientations previously outlined were chosen primarily with build time in mind. In regards to infill percentage,the components were ranked in order by longest anticipated build time to shortest (Table 1). The components with the shortest build times were often the smallest and therefore were granted 100% infill. The larger components such as the body and crank assembly needed their infill percentages to be minimized, but could not compromise build strength.
- Part Strength
The part strength of each component is dependent on the build orientation as well as the infill percentage. As previously mentioned, the orientation of the smaller components was largely irrelevant and a high infill percentage is easily achieved with minimal loss of time or added weight. This allowed high strength in all smaller components. The body and crank mechanism required further consideration because the build time would need to be kept in check by lower infill percentage, while maintaining a high strength since they are critical components. For this reason, a “happy medium” infill percentage was decided upon of 30% for the body, and 50% for the crank assembly. Lastly, fiber orientation was important for both the bow and the body. In each case, an effort was made to align the fibers so that they are loaded axially. This meant that fibers run the length of the body and the length of the bow.
Table 1
