I like Engi 210 midterm project in that it is an integrated task that requires all the designing and prototyping skills we have learned before. For this project, I chose to make a cool crank slider mechanism that can be widely observed on the old-fashion trains that I like.

 

I start my mid-term project by trying to cut out the illustrator drawings I have to make a low fidelity prototype. I at first thought that this prototyping work should be a piece of cake, as I have a pretty great illustrator drawing for my previous homework. However, things did not turn out to be smooth as I expected, because my old illustrator drawing has two big problems:

1. The drawing contains many extra lines that should not be cut. For example, I have three concentric circles for my flywheel drawing, but only one of them should be cut out as the other two circles are just used to demonstrate the difference in thickness.

 

2. The drawing did not include the holes of the dowels and thus the pieces I cut out cannot be assembled.

To solve these two problems, I revised my previous illustrator drawing. I try change my old 2-d drawing in a 3-d way and trying gain the thickness by piling multiple layers of wood together. For example, I piled three layers to make my flywheel. I put a disk with hollow texture in the middle and sandwich it with two circular rings.Moreover, I measured the diameter of the dowels and made holes on my pieces so that the dowels can be directly inserted.

Revised Drawing (The ai file shows how I turned 2-d into 3-d made up of layers. Yet it was still a crude draft as it has other problems.)

(Sandwich structure)

 

The revision helped a lot. With that, I successfully made a fly wheel and a fly wheel stand. However, the crank and the slider was still a challenging problem. During the process of building this low fidelity prototype, I realized that after install the flywheel and the slider on my basement, the front surface of the flywheel and the slider are not in the same plane, which stops the crank slider mechanism from working.

 

I realized then that I need to consider the thickness of the wood as a part of my design. To solve the problem, I measured the thickness of the wood plate, did some calculation and revised my design. In order to get a better effect, I prototyped with several different materials and decided to use the .016 inch plywood board.

(Trials on different types of wood materials)

The next challenge I encountered was to find a way to connect the crank and the slider. In order to achieve great performance, I need a really thin cylinder to serve as a shaft. I searched the wood supplies of OEDK, but I found the thinnest dowel was way larger than ideal. I thought of using paper clip, but it was hard to cut it into the ideal length without bending it. With the help of Doctor Wettergreen, I end up finding an interesting solution, the toothpick. The tooth pick is thin, smooth and can be easily cut. I measured the diameter of the toothpick and laser cut a whole on my slider and inserted toothpick into it. It turned out that the tooth pick shaft was beyond my imagination.

(Toothpick shaft)

 

Now that I solved my major problems in design, I started making my final product. During the process, I came up with several interesting ideas to make my crank slider both look better and work better.

 

1. During the tests, I found that when I turned the flywheel, it had unwanted movement in Y direction. To solve the problem, I drill pressed the dowel and added a small piece of toothpick as a locker. It works perfectly.

(toothpick lock)

2. In order to fixate my .5 inch dowel from sliding, I added two circle plates on each side of the dowel and glued them to the slider track. They look great!

 

3. I used the laser cutter to engrave logos and names on the basement of the crank slider. So when other people see it, they will know what mechanism the device is demonstrating, what class is this for and who made it!

(My first trial of the engraved board. I used a better version for the final product)

4. I press drilled a ball and arranged it at the end of the handle so it is easier for people to turn the fly wheel.
5. I changed the structure of the flywheel and put the original middle part on the last layer to make it more stable.

 

Also, during the finishing process, I sanded the surfaces of the slider and the slider track. Lubricate all the contacting surfaces with animal fat to make the movement smooth. I thought of spray painting a clear paint, but it didn’t help much as the plywood itself has a very beautiful surface texture. So I end up not spray painting it.

 

I aimed at building a perfect device, but I have to admit that my final product is not perfect. For each round, the device experiences two small “knock points” when the player will feel a slightly larger friction of the wheel. This happens when the slider reaches the ends of the sliding track. I tried to solve the problem by adjusting the location of slider, but it did not help much. Yet, I feel this is a happy imperfection as the knock points add a rhythm to the slider system.

I’d like to end my blog with pictures of my cool crank slider system. It is theoretically my first piece of wood work. I really enjoyed the experience of making it and I love it sooooooooooo much!