For the class midterm I designed a mechanical device that would mimic motions from the 507 Mechanical Motions. I chose to implement two of the motions into my design, numbers 329 and 493 (pictured below).
Motion 329 translates rotational motion of a wheel into linear motion of a piston using a set of planetary gears. I decided to use the linear motion of the piston to control motion 493, which uses three wedges to lift and release a block.
My first step was to draw by hand how I would combine these two mechanism and also how the components of the model would act together. I was most concerned with the axels in the planetary gear and how I would secure components in place while allowing others to freely rotate. The animation on the website was incredible helpful, but it did not show me the layering of the components; they all appeared in one plane, which cannot be the case physically.
My hand drawing of the design’s moving parts (above)
This drawing proved to be incredibly helpful later in the design process. It helped me visualize how all the components would be glued together, and also how thick some points needed to be. After drawing the design, I realized that I would need support in many spots to prevent the entire design from breaking apart. I added strength by doubling, and even tripling, the layers of wood at some points.
My next step was the design the entire device in SolidWorks. I chose to use SolidWorks over Adobe Illustrator because I felt more comfortable with the program and SolidWorks would allow me to create a 3-dimmensional assembly of my mechanism. I decided on some rough overall dimensions and began to create the base and support beams. The supports all have “teeth” that fit into specific slots in the base, and dowels would be used to join the several layers of support.
(Pictured below: upper– image of SolidWorks assembly supports triple layered for strength and mortis jointed together. lower left: full assembly of mechanism, lower right: base plate with “teeth” slots to easily connect components in correct locations.)
One component on the project must be cut on a plasma cutter, and ideally that piece would be one of the moving parts. I faced a tough choice, plasma cutting is not very accurate (compared to laser cutting), but the moving parts in my mechanism needed to be incredibly precise to function properly. My solution was to find a piece where accuracy did not matter, but was still a moving part, to serve as my plasma cut component. The massive 8inch drive wheel on the back of my mechanism would be made from a solid piece of ¼” thick 6061-aluminum. This was the first component I cut and I polished it for an hour or so to get a mirror like finish.
The most critical parts of my design were the planetary gears. I did not know how to properly make gears in SolidWorks, but Dr. Wettergreen and Dr. Hunter showed me a few great websites that would produce the gears for me. I downloaded the files as .dxf type files and then converted them into SolidWorks with the proper dimensions afterward. At this point I began to laser cut many of the pieces I had designed out of wood. I decided to skip the cardboard step because with my SolidWorks assembly I was fairly confident all the pieces would fit together. I also cut ½” dowels to the proper lengths and laser cut several spacers and stoppers I designed to hold my rotating components together. Since all of the wood I was using was the same thickness (0.2” thick) it was easy enough to layer everything and orient it to fit together.
Rather than go through every single step in the process, here are all the problems I faced, and how I solved them:
What will the piston lift?
I did not know what to have my piston lift and I was not sure how best to make it. My first thought was to laser cut a bunch of pieces and glue them together to form a block of the required shape and size. This seemed a little ridiculous. I decided to instead manually mill a block of 4” by 4” cedar wood to form my block to lift. I used a fly cutter to square off the block, and a ½” end mill to carve out the channel in the middle. Then I spray painted it blue to make it stand out as the focal point of my mechanism.
How to keep the block in place?
So now I had this block, but how do I stop it from falling off my piece when it’s not in use and getting lost? I thought of using strings for a bit, and then I liked the idea of using 4 pillars, that the blue block would slide on, to keep it all in place. Dr. Wettergreen pointed out that this would likely bind and prevent movement, and suggested I try two thicker poles instead. I implemented that in my final design, using two ½” dowels and it worked extremely well.
Painting and Staining:
Every component needed to be either painted or stained to have a nicer finish than the bare wood. My first thought was to paint every piece, but then I realized then my mechanism would look like a jumbled mess of colors. I decided instead to paint only the key components that were part of the device’s function. This way, the moving parts would stand out to the viewer, and the supports could fade into the background. I chose simple colors what worked well together; black, blue, and silver. For the rest of the pieces, I used a turning finish oil that brought out the color of the wood, but was not a full stain. This oil gave me a softer finish to the wood, but still maintained close to the natural color.
Lack of support:
When I first began to use my device I discovered a serious problem; the weight of the block caused the gears to become unmeshed as the user rotated the disc. I needed a way to lock the two gears together, but yet preserve the viewer’s ability to see the gear teeth meshing. On-top of that, I needed to work around my existing design because it was already glued together. I first thought of adding two acrylic rings to hold the gears together and they would be see through, but I did not think I could attach the acrylic in such a way that it is not detracting from the look of my piece. Instead I went back to SolidWorks and designed a “rib” shaped arm that connected my two main support structures, and added a ring of wood to the back of my planetary gear. These pieces had to be fit into the design as it was, so SolidWorks assembly features were incredibly helpful.
This project was a fantastic experience and education opportunity for many skills I had never stretched to this capacity. I learned much more about post processing wood, laser cutting complex assemblies, and the amount of buffing necessary to bring out the shine in a block of aluminum 6061. I’m really satisfied with how my mechanism turned out and I hope other people enjoy operating my ENGI 210 midterm project.
