Bottle Opener

Hello again friends!

Our first assignment in ENGR 160 was to make a bottle opener that could open a non-twist-off bottle cap. The bottle opener had to be cut on the laser cutter from a single sheet of Delrin (the brand name for Polyoxymethylene - a type of plastic) no greater than 6"x6". I worked with Angel Kuo, a classmate. 

Process

We started out by brainstorming approximately 20 ideas in about 10 minutes. As some of these ideas were completely ridiculous, or did not follow the directions, or wouldn't work in any way, shape, or form, we ended up narrowing our list down to 10 different designs:

Original Brainstorm

We further narrowed down this list based on various physical aspects to maximize the likelihood that the bottle opener would easily open the bottle and not break or degrade while doing so. The first 4 designs (left to right) were discarded because our Delrin sheets were not strong enough to withstand the necessary force at the fulcrum of the lever (where the edge of the handle presses onto the edge of the bottle cap), while still remaining thin enough to fit under the edge of the bottle cap.

Engineering Analysis

We analyzed the potential deflections of the handles using a cantilever beam deflection equation:

deflection = (FL^3)/(3EI)

F=force, L=length, E=Young's modulus, I=area moment of inertia

In this equation, the Young's modulus (E) is set because it is dependent on the material stiffness of the Delrin, and the force (F) is uncontrollable because it varies depending on the user. The only variables that we could actually control when designing our bottle opener were the length (L) of the handle and the area moment of inertia (I), which is dependent on the stiffness of the cross-sectional area. To get as small of a deflection as possible, the handle length for these designs needed to be as short as possible, as the area moment of inertia (I) would be rather high in a design where the pressing surface of the bottle opener was across the thickness of the Delrin sheet. 

We knew that the Young's modulus (stress/strain)(E) for Delrin was 410,000 psi and that the proposed length (L) for each handle was around 2" and the width was around 1". The area moment of inertia (I) for a 2" by 1" handle would be ((LW)/12) = (1in*2in^3)/12 = 2/3 in^4. The total force (F) applied to the bottle opener would depend on the user and was thus uncontrollable. Thus,

deflection = (F lbs*(8 in)^3)/(1,230,000(lbs/in^2)*(2/3 in^4) 
= (F*512 in^3)/(820000 in^2)
= 0.000624F in

Original Brainstorm

The next 3 designs and the design in the middle of the bottom row were discarded because they were all intended to hook under the edge of the bottle cap and roll down the outside of the bottle, pulling off the cap. However, we realized that this would only pull a small section of the bottle cap edge out and away from the bottle, rather than pulling the bottle cap all the way off. 

Both of the remaining designs (bottom left and bottom right) were very similar in function: the hook went underneath the edge of the bottle cap and pulled up while the top section of the bottle opener pressed on the center of the bottle cap, creating a fulcrum around which the cap bent. We ended up choosing the design on the bottom right because it was both more aesthetically pleasing and less likely to chip/break or to pierce the bottle cap. We knew that if we chose either of these designs, we would use the thickest possible Delrin sheet (1/4"), so that the bottle opener would be as strong as possible. Because the pressing surface of these bottle openers is the thickness of the Delrin sheet, the pressing surface could be as large as possible and it still wouldn't affect the ability of the bottle opener to hook under the edge of the bottle cap.

Engineering Analysis

We again calculated the possible deflection of the length of the bottle opener, which was analogous to the beam of a cantilever:

deflection = (FL^3)/(3EI)

F=force, L=length, E=Young's modulus, I=area moment of inertia

Again, we could only control the length (L) of the handle and the area moment of inertia (I). To get as small of a deflection as possible, the handle length for these designs needed to be relatively short, but could be somewhat longer than in our other designs, as the area moment of inertia (I) was lower because pressing surface of the bottle opener was parallel to the thickness of the Delrin sheet. 

We knew that the Young's modulus (stress/strain)(E) for Delrin was 410,000 psi and that the proposed length (L) for the handle was around 2" and the width of the cross section was 1/4". The area moment of inertia (I) for a 2" by 1/4" handle would be ((LW)/12) = (1/4in*2in^3)/12 = 2 in^4. The total force (F) needed to pry off the bottle cap would remain constant between each design. Thus,

deflection = (F lbs*(8 in)^3)/(1,230,000(lbs/in^2)*(2 in^4) 
= (F*512 in^3)/(2460000 in^2)
= 0.000208F in

This is less than the handle deflection of our other designs, so we picked this design to move forward with. 

After choosing our preliminary design, we started refining and went through a couple of iterations:

Bottle Opener Design Iterations

1. This was our original design, copied from our brainstorm.
2. We lengthened the whole design in order to create more leverage when opening the bottle.
3. We thickened the hook in order to reduce the likelihood of it breaking, as the hook is where a large part of the force is concentrated.
4. We decreased the diameter of the circle at the top of the opener, so that it stayed on the bottle cap as it was rolled over.
5. We decreased the distance between the hook section and the circle section, so the circle hit the center of the bottle cap while the hook was under the edge of the cap. We also thickened the whole bottle opener to increase its strength and rounded out the whole design to make it both more aesthetically pleasing and more comfortable to hold. 

Our next step was to create a prototype out of foam core:

Foam Core Prototype 1

We held this prototype up to a sample bottle and realized that the circle still did not hit the middle of the bottle cap, but was instead closer to the edge, which would make it more difficult to bend the cap and pop it off of the bottle. So we made another iteration of our foam core prototype:

Foam Core Prototype 2

Prototype 2 had a shorter distance between the hook and the circle, so the circle landed in the middle of the bottle cap. We lined this foam core prototype up with our sample bottle and double-checked that it fit correctly, and then we moved on to building our model in SolidWorks, the program that we use to send designs to the laser cutter.

We had a bit of trouble with SolidWorks, mostly just because it has an insane learning curve. I'd only used it a little bit and not in a long time and Angel had never used it, so we were basically starting from the beginning. 

After we drew the part in SolidWorks, we had to transfer it from one computer in the engineering lab to another computer across the lab. This was inordinately difficult. We were the first group to finish building our design in SolidWorks and thus the first to try to transfer our files. We had to be able to open this file on multiple programs on the other computer, notably Corel Draw. We originally tried to use a DXF file, but this wouldn't open correctly on Corel Draw. After about 45 minutes and 10 different file types, we finally got the file to open.

Next, we learned how to set up the laser cutter, including how to load materials into the laser cutter and how to adjust the laser so that the focus is on the surface material. We set the material type, power, velocity, and number of passes, then sent the file to the laser cutter. The laser cutter's first cut didn't cut all the way through the Delrin, so we adjusted the settings and tried again. After a couple of tries, the laser finally cut through the material and our bottle opener was finished!

Final Delrin Bottle Opener

We tested out our bottle opener on a sample bottle and found that it easily worked without degrading at all, indicating that it could be used multiple times, so we were finished!

Reflection

I think this project went relatively well, especially considering our distinct lack of prowess with SolidWorks at the beginning of the project, and I'm pleased with our final product. That being said, I wish we would've made our bottle opener a little bit more aesthetically appealing. It isn't exactly displeasing to the eye, just utilitarian. However, I worry that cutting shapes into the middle of it for decoration would have weakened its overall structural integrity. Anyway, it kind of looks like a slug or a one-eyed monster, which is pretty awesome, and it works really well!

Thanks so much for reading! See you next time, when we'll be designing well windlasses!