For our midterm project, Pablo and Sarah proudly present… OEDK on Ice!

Read on to learn how we created our frozen lake with figure skaters gliding along.

When we were planning what to build, we knew we wanted some sort of back and forth motion with a turning element as well, which made us think of an ice skating or dancing theme. We spent a while searching 507 Mechanical Movements until we came across number 269, the mutilated rack. This motion shows a gear that turns one way and then the other as it encounters racks on opposite sides of a frame. We’d also need a way to turn those gears from side to side, so we chose movement 96, the cam. We’d start by using a handle that would turn a set of gears, which would in turn rotate the cam, and the cam follower would move the gears in the frame.

To start, we designed the various pieces of our model, focusing first on the top gears and racks. We were originally going to cut them by hand out of cardboard, because we had assumed cardboard would catch fire in the laser cutter. It turns out, however, that you can laser cut cardboard, you just need to turn the power down. We cut two different sizes of gears, but we noticed that the shape of the teeth wasn’t quite right, and they weren’t fitting together or turning smoothly.

Over the next few days, we adjusted the shape of our gears, cut the cam and follower, and cut the sides of the box. For gate 2, we had a somewhat working cardboard model! The bottom two gears (the main drivers of the motion) were working well, but the top gears (where the figure skaters would be) weren’t turning as smoothly as we’d like. However, we talked it over with Dr. Wettergreen and decided to wait until we had cut our pieces from wood to see how they would work.

Next up, building with wood! We didn’t make any major sizing changes between our cardboard model and wood model, but we did recut our gears using Evolvent Design so that they would be proper involute gears that would fit together nicely. For this phase, we needed to spend a lot longer assembling so that we could get a good sense of whether things would move together smoothly. We cut out our pieces and had to do our gluing and assembly in phases, allowing the first pieces to dry before we could continue attaching them to other pieces. This turned out to be one of the hardest parts of the project, and set us a little behind schedule for gate 3. We had many small pieces such as keys for all of our gears and three layers for the cam housing. We also had some trouble getting dowels that fit perfectly into the holes we had cut, so we had to add extra glue, and doing this for many small parts really added up time-wise. Also, we wanted to cut our cam and cam follower out of aluminum, but hadn’t had a chance to use the water jet cutter and add that to the assembly, so we weren’t positive it would work. Eventually, though, we built our wood model, minus the post-processing.

For the final phase we moved onto the final build, post-processing and aesthetic embellishments. As we were planning out paint colors and wood stain, however, we realized… will a metal cam and follower be too heavy to suspend from the top of our mechanism? We didn’t feel we had enough time to recover if something were to go wrong, so we pivoted our design slightly. Instead of the cam and follower, we cut a Scotch yoke out of wood, and made a metal handle for our functional piece.

Although I was a little nervous about making a last-minute change, it allowed us to go into post-processing with more confidence. Since we were running out of spray paint, we chose to go with a mostly monochrome look and only stained our wood with teak oil. A few pops of color came from the vinyl stickers we made for our skaters’ dresses. On Sunday afternoon, however, we found light blue paint! Perfect for a frozen lake! With everything painted, we assembled the top of our box and were able to admire how all our pieces fit together. For a final touch, we added some snow-capped trees. Thanks to the Noun Project and some quick adjustments in Illustrator, we made 3D wooden trees using two pieces that notched together, and used the last dregs of white spray paint for a sprinkling of snow.

Challenges of the project:

• Laser cutter reservations
• Running out of paint
• Time spent waiting for glue to dry
• We probably could have simplified our design and avoided many of the small pieces we had to deal with.

Strengths:

• Success with the water jet cutter
• Smooth gear mechanism
• Creativity and flexibility with decorations

Cost analysis:

Cost	Price	Amount	Source	Quantity	Unit	TOTAL
2″x12″ .5″ thick 2024 aluminum	$50.61	0.167	OnlineMetals.com	0.0378	sqr ft.	$11.48
2x4ft Board 1/4” thick	$21.98	8	Lowes.com	24	sqr ft.	$65.94
24″x48″ Corrugated Cardboard	$8.04	8	Staples.com	24	sqr ft.	$24.12
Waterjet cutter operator	$18.00	per hour	Ziprecruiter.com	1	hours	$18.00
Prototype/Designer/Development (Woodworker)	$19.00	per hour	Ziprecruiter.com	38	hours	$722.00
Facility & tooling cost	$250.00	per month	txrx.org	40	hours	$13.89
Waterjet cutter time	$30.00	per hour	omax.com	1	hours	$30.00
Quality Control	$18.00	per hour	Ziprecruiter.com	1	hours	$18.00
					NET TOTAL	$903.43

Link to slides