Our first project in Engineering 160 this semester was to make a bottle opener. And as a naive newbie to engineering, I suspected no challenge would come out of making such a simple tool.
I have come to respect bottle openers (or at least their engineers) more after brainstorming for, designing (multiple times), making prototypes of and testing bottle openers for over a week.
Bottle opener as a cantilever:
On the first day, we discussed the formulas for the deflection of a cantilever and modeled the tip of the bottle cap on which the opener applies force, as well as the opener itself as cantilevers.
We used the following relations to get a general sense of how to minimize the deflection of the opener while keeping it long enough to apply enough force that can open the bottle cap.
where delta = deflection (displacement of the tip);
F = force applied on cantilever;
E = young's modulus (a constant value of 2.6 GPa for Acetal and 180 GPa for stainless steel);
L = length of cantilever from fixed end to the tip
and I = moment of inertia which is obtained from the formula,
Image 1: Cantilever deflection
Let's get sketching!
During class time on the first day of the assignment, we sketched a few possible designs. What all our designs have in common is a part that goes under the cap to apply an upward force (to uproot it) and a part that would hold down the cap from the top to fix it in place.
Image 2: Rough sketches of possible designs
Image 3: Candidate that stood out
The bottle opener design shown in Image 3 stood out as the "cantilever" that is the least likely to bend as it is short (small L) and wide (large B). And we know from the deflection formula that 
and 
.
After a brief consideration of a rectangular piece to go under the bottle cap, we figured a curved tip would be less likely to get chipped.
Foam core model:
We went on to make a prototype of this design out of foam core. We measured the diameter of the top of a bottle cap (~2.7cm) using a caliper and made a circular opening just as big in our "opener." We cut out the inside of the opener, the part that would directly contact the cap as shown in Image 4. Then, we carved out the body of the opener (shown in Image 5) such that its maximum length x base measured 10 cm x 5 cm.
Image 4: Bottle opener part measured to fit over the bottle cap
Image 5: Top left: Cork with measured diameter (victim); Top right: Knife (trusty assistant); Bottom left: Carved out bottle opener; Bottom right: Circles making up the opening of the opener outlined
We tried to fit the carved out model with the nice curve and applied some pressure (pretending to open the bottle) and realized that the thin sides of the circular hole bend very easily. These sides are on the horizontal line connecting the intersections of the two circles marked in Image 5 above. Although foam core is much weaker than Acetal, this still shows that thin sides are more likely to break under pressure.
So we designed the opener such that two diagonals between the two circles would provide more support as in Image 6 below. We also decided to model the frame of the opener as a rectangle to prioritize functionality over aesthetics.
Another problem we noticed: The part of the opener that passes the diameter of the cap is actually narrower than the diameter of the opening. So we made the diameter of the circle 3 cm to give some room for the cap to fit.
Image 6: Bottle opener model slightly modified for better strength and fit
On to SolidWorks:
Image 7: SolidWorks sketch of bottle opener Version #1
We converted the SolidWorks parts document to a dxf document for the laser cutter.
Then came the exciting part of using the laser cutter to carve this design out of acetal! With Xi Xi's help, we positioned the acetal under the laser cutter, adjusted the height, and cut the acetal into the right shape with the flame of the laser.
Image 8: Laser cutter at work
The laser cutter literally burns parts of the acetal corresponding to the lines in the sketch. The opener looked like this as planned:
Image 9: Laser-cut acetal bottle opener (First version)
Opener to the test:
Filed the curvy tip such that it fits under a tight bottle cap (Image 10), and tried opening a tightly sealed bottle. It worked for 3 out of 4 people we tried.
Image 10: Filing down the curvy tip of our bottle opener
Image 11: Bottle Opener #1 works!
While we were excited it worked for the most part, we noted that the pointy edges make it less comfortable to hold. We also observed we may need more space at the top of the opener for two fingers of the user to rest comfortably and hold the bottle and the opener together as a fixed pivot point.
Second iteration (or third, since a new friend joined us):
We designed our second iteration such that its edges would be curvier and its shape more comfortable for the user. The SolidWork sketch looked like this:
Image 12: SolidWork sketch of bottle opener mode - a more comfortable grip
But our next iteration got more interesting when Marissa, with her own first version for a bottle opener, joined our group. Now the task was not only touching up our original design for a more comfortable grip but also integrating the two very different designs into one.
This is what Marissa's design looked like:
Image 13: Marissa's original bottle opener design
So we decided to make a double sided opener, our different designs at each end. The second bottle opener need to have a tighter fit on the bottle cap to minimize the effort one needs to open the bottle.
As we worked to combine the designs and because we are still learning to use SolidWorks, we created an accidental curve at one edge that resembled a bird's beak.
First reaction: Oh no! What did we do?!
A few seconds later: Hmm, this actually looks like a bird now. Let's keep it!
So we measured the beak-looking edge to fit the bottle cap from the top such that the pointy edge grasps the cap from the side opposite to the user. And we kept it as a third opener.
Here is what our final SolidWork design looked like:
Image 14: Final SolidWork design of our bottle opener
Having three openers allowed us to have a nice design of a bottle opener that resembled a bird with its egg (Trust us. Look closer, and you can't unsee it.) It also turned out to be safer given the brittle material.
As a tip, and an artsy component, we made an eye for the bird which can also fit a key chain.
Take a look at the three generations of our bottle opener:
Image 15: The family of bottle openers we managed to make
Why is the final iteration better?
* It is easier to hold as its edges are filed or curved
* It is long enough to allow for a greater torque and a more comfortable grip. But it is still short enough to avoid bending.
* Depending on your preference, you have 3 openers to choose from in one relatively small design.
* It looks prettier.
Acetal is strong and hard but chips very easily when scraped by the pointy edges of a bottle cap. So I would use steel or another more malleable but strong material. I would also file the curvy opener tip to make it fit under the cap better.
Thank you for reading my blog! And get excited for many more to come!
Best,
Mebatsion Gebre (Meba)
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