My engineering analysis of our bottle opener indicated that its max stress would be 69 MPa, which is one MPa under the yield strength for acetal. It makes sense that our opener chipped when we applied a lot of force. According to the equations for area moment of inertia and max stress shown above, in order to decrease max stress in our opener, we needed to decrease the applied force (which is harder to control) and the length while increasing base and height. Height is the most important factor since it is squared in the denominator of the resulting max stress equation. On our first iteration, we used the thinnest plastic, 1/8". For our next design, we went with the thickest option, 1/4". We needed to decrease the length of the opener without compromising ease of use, and we found that a 6.5 cm handle seemed like a good length. We also needed to increase the base, the length of the opener that comes into contact with the cap. Our previous design barely came into contact with the cap, so we decided to try a new design.
This design has a small curved hook that goes under the cap and a long arm that provides leverage on top of the cap.
A sketch with exact dimensions
The drawing of our part in SolidWorks
The final product
The final step of our process was filing down the sharp corners so that they wouldn't hurt the user's hands.
Our final design was very quick and easy to use, but if given more time, we could improve on its aesthetics by adding engravings or shaping it like something more interesting than a bottle opener. We could also brainstorm ways to make the handle more comfortable (which would probably involve it becoming more cylindrical instead of rectangular and couldn't be done with the laser cutter) and add some convenience features, such as a keychain.
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