The goal of this midterm was to create a mechanical model from one of the movements in 507 Mechanical Movements. I chose mechanical movement #283 which can be found here.
When I first saw this movement, my eye caught the rod in the middle moving back and forth and envisioned that as a ping pong ball moving back and forth between two paddles. I began by creating many sketches of the individual parts on Illustrator. I created the sketch of the central gear using geargenerator.com, taking a screenshot, and then using image trace to get the sketch. I created the sketch of the gear racks by tracing a screenshot of the original mechanical movement. I made the ping pong paddles by taking an SVG from here. I sketched a part to act as the “ping pong ball”. I drew a trapezoid as a stand for the central gear and made rectangles to hold the gear racks in place. I made holes in the center of my parts so a 1/4″ dowel rod can fit through the parts. After creating my first sketch, I used the laser cutter to create a low/medium fidelity prototype using cardboard.
I first attached the trapezoidal stand to the base. I then glued the knob, gear, and ball component together to create one rotating component. I put a paper straw through the holes of the rotating component and also through the trapezoidal stand. I then made small containers to hold the gear racks in place and attached them to the base. Finally, I put the racks within those containers. Although I was able to confirm how everything was able to fit together, the flimsy cardboard made it hard for any mechanical movement to occur.
To test if my contraption was even capable of movement, I then moved on to making my first wooden prototype. I found that a setting of 3 speed, 10 freq, 100 power worked best for laser cutting 1/4″ birch plywood. After putting everything together using wood glue, I noticed that several problems had to be addressed. The first one being that the gears weren’t lining up that well. There was a lot of friction between the gear rack holder and the gear rack, so I had to sand down the bottom of the gear rack and add Vaseline to it. Although this helped, the gears moved very inconsistently and it was still nearly impossible to move the central gear.
Another problem that was also a cause of the gear not working well was that the central gear, ball component, and the knob at the end of the dowel all caused it to tilt downward, misaligning the gear from the gear rack. I tried laser cutting a disk to put on the backside of the trapezoidal stand to hold the rod in place better. However, this only had minimal results, as the dowel rod still tended to tilt downward.
The trapezoidal stand and gear rack holders were also not perpendicular to the base which also affected gear alignment. This is probably due to the laser cutter not cutting in a perfectly vertical fashion, and imprecise gluing on my end.
I also realized that the trapezoid and the ball component was a bit too tall for the ping pong paddles to be put at a reasonable height. For this reason, I shortened both of those parts in later iterations. The central gear was also a bit too thin for the gear racks to catch on consistently, and for this reason I decided it would be a good idea to double up on the gears in the future.
I also had to figure out where to put the gear racks in relation to the gear so that the ball would tilt in either direction in equal amounts. After a lot of trial and error I used a pencil to mark which teeth of the gear aligned with which teeth of the racks.
I ended up making two prototypes completely out of wood to experiment before I made my final prototype.
For my final prototype I also made many edits.
I made the knob bigger, as it was too small for it to actually be effective as seen above. I ended up triple layering them so the user could actually get a good grip on them. I also made the “ping pong ball” on the end of the ball component larger so it was more proportional to the paddles. The base was also extended to allow room for the ping pong paddles.
Another big change that I made to solve the issue of the rack holders and the trapezoid not standing perfectly straight was to double up the base. This allowed me to add slots on the top layer to better hold those parts in place. This worked wonders and saved time for me, as I was just able to glue and put the gear rack holders quickly into place instead of trying to estimate where the best place to put them was. I also no longer had to worry about those parts tilting in a certain direction. I later used mahogany stain on the base, the trapezoidal stand, and the knob.
I used the water jet to create my mechanical component, the central gear. I used 1/4″ aluminum to make this gear. As said earlier, I created two gears to allow for plenty of space for the gear racks to catch on.
One issue I ran into with these gears is that the hole for the dowel rod was a bit too small. I had to spend an unreasonable amount of time sanding down the inside of it using sandpaper and files. If I had made the hole a little bigger, I would’t have wasted more time.
For aesthetic purposes I laser cut the ball component out of acrylic. I put the three knob pieces together using wood glue, and used epoxy to put the knob, the two gears, and acrylic part together. As seen above, I was still having the issue where the knob and the gears weighed down the dowel downwards. I was finally able to fix this recurring issue by adding two metal bearings on the back to balance the dowel rod as seen below.
After putting mostly everything together, the gear worked in a much smoother fashion than my previous iterations. I still had to sand down the gear racks profusely to make them move up and down as smoothly as possible. However, I noticed that as the gear racks moved upward, they tended to be pushed out to the side by the central gear, causing some hiccups in the movement. To fix this issue I laser cut and glued some pieces to hold the gear racks in place further upward from the containers, to prevent them from being pushed horizontally. This can also be seen in the above picture. It turns out that this was the icing on the cake, as after applying Vaseline on the gear racks and gear, the gear was able to rotate very smoothly. All that was left were the ping pong paddles.
I used the plasma cutter to cut out my ping pong paddles for the aesthetic component. I used 1/8″ stainless steel. For the plasma cutter I used a feedrate of 40 with a .125″ arc lead in. The picture above shows what they looked like before post processing.
The picture above shows what the paddles looked like after post processing. I used the angle grinder, stone grinder, wire mesh, and files, and sandpaper to post process them.
I then spray painted them red and black on each side of the paddle. I used painter’s tape so the handle did not get painted on. After the paint had dried, I put on a layer of gloss clear coat. I was actually pretty impressed with myself after how well they had turned out. I did much better with the paint job than my plasma cut diamonds.
I then made the stand for the paddles. I used the laser cutter to make the cylinders to hold the paddle in place and a 1/4″ dowel to raise them to the correct height. I used super glue and wood glue to put it together.
I then finally used wood glue to put the two paddles in place on the base of my machine. My machine was finally complete. When you turn the knob in the middle, the ping pong ball hits the paddles, making a very satisfying clinking noise. The link below is a video of how my machine moves.
Overall, I am very proud of what I was able to make. The gears ended up moving much smoother than expected, and visually it was exactly how I imagined it to be. The final result had made my hours upon hours of stressful work worth it. I learned so many things from this midterm; from specific things such as wood staining and getting more comfortable with Illustrator, to more broader lessons like the importance of trial and error, and order of operations. One thing I would change about my machine is the aesthetics. The presentation of my machine is kind of sloppy, so if I had more time I would have stained all of my wood parts and tried to make the gluing less noticeable.
Cost Analysis:
3 1/8″ thick 24″ x 32″ sheets of plywood from the OEDK = $15
Stainless steel (6″x18″ at Home Depot): $7.45
https://www.homedepot.com/b/Hardware-Metal-Sheets-Rods-Sheet/Stainless-Steel/Steel/N-5yc1vZc27vZ1z0r6yiZ1z116eq?storeSelection=577,6985,566,6806,6525
1 1/4″ thick 24″ x 32″ sheets of acrylic from the OEDK = $5
1 12″ x 12″ sheet of aluminum: $6
Epoxy: $3.6
https://www.amazon.com/Loctite-Instant-0-47-Fluid-Syringe-1365868/dp/B0044F9KFI/ref=asc_df_B0044F9KFI/?tag=hyprod-20&linkCode=df0&hvadid=194918515178&hvpos=1o5&hvnetw=g&hvrand=15182763917090331287&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027605&hvtargid=pla-311721580921&psc=1
2 cans Spray paint ($4 each at Home Depot): $8
https://www.homedepot.com/b/Paint-Spray-Paint/Rust-Oleum-Painters-Touch-2X/N-5yc1vZapz5Zbm2
1 can clear gloss: $4
Waterjet (30 mins at $20/hr) =$10
https://wardjet.com/tools/waterjet-cost-calculator
Plasma cutter (30 mins at $55/hr) = $27.5
https://www.plasmaspider.com/viewtopic.php?t=8162
Laser cutter (1 hr at $12.73/hour) = $12.73
https://fsmdirect.com/cutting/laser-cutting/75-co2-versus-fiber-laser-cost-to-cut-a-part
2 bearings: $5
Handtools/post processing tools: $10
1/4″ dowel rod: $1
3/4″ dowel rod: $1
wood stain: $7
https://www.homedepot.com/p/Varathane-1-qt-Red-Mahogany-Classic-Wood-Interior-Stain-339709/305502014
Labor (25 hr at $12/hr) = $300
Total: $423.28
