I began this project by attempting to trace the following shape from Five Hundred and Seven Mechanical Movements:
After importing the above drawing into Adobe Illustrator and fiddling with the tracing settings for some time, I determined that the original drawing was not of sufficient quality or geometric regularity for the task. There was no “modernized” drawing included for these gears on the website. The image below shows the result of this attempt:
As can be readily observed, the drawing that resulted, even after fairly significant gap-filling to yield a close representation of the original drawing, was still fairly irregular-looking.
Since the project was already over-budget for such a simple task, I endeavored to pick a similar design which had a modernized drawing included on the site:
Movement #24. Not only did these gears prove significantly easier to trace and edit, but they yielded a much more geometrically sound drawing. First, I custom-traced the gears using the following settings:
Next, I expanded the trace and edited and joined problem areas to form continuous lines throughout. The middle section below was fixed and the gears were separated, as shown below.
Finally, I added the dowels that would be necessary. It would be fairly unorthodox to stack cut circles to make a dowel, but they were requested by the assignment so I added them below the gears by copying the center of each gear and making it slightly smaller, to allow the dowel to be inserted into the hole at the center of each gear.
All said and done, the project including the initial failed effort took approximately 4 hours to complete. If I were actually trying to laser cut working gears like this, instead of trying to create a file that replicated the image on the website precisely, I would import the image into Fusion 360 and create a sketch of one tooth for each gear, then use a circular pattern to create a perfectly round and symmetrical gear. The process would yield a product of much higher quality and probably take around 30 minutes to complete. How much did it cost to create this file? well, there are many ways to interpret that question. How much does it cost Rice? How much does it cost me?
As for Rice, the cost was incredibly small. The amount of energy used is negligible at the current rate per kwh, and I only used Illustrator for four hours, where a single yearlong subscription costs only around $240 for an entire year (240/(365*(24-8)) = $.04 per hour) and Rice likely pays far, far less than that per subscription. Therefore the cost to Rice was probably in the ballpark of $.05-.10.
On the other hand, Rice students pay about $25,000 per semester to attend. The cost per hour: 25000/((24-8)*102) = $15.31. This includes every single day of the semester. Therefore the opportunity cost to me for completing this project was around $60. This puts Rice’s profit at around 590% for this particular project. Not bad for the endowment.
A link to the Ai file corresponding to the above discussion:
