# Making something big

### Computer controlled machining and giant beachballs

This week was about large-scale machining on the ShopBot (and optionally the Water Jet cutter). I decided to use the week's assignment "Make Something Big" to try to fabricate my giant inflatable public sphere that I'll need for my final project. I want the sphere to be transparent so after looking over some various plastics and doing some research into beachballs, I ordered thin, clear vinyl from fabric.com.

How big is something big? Well, I want my networked public sphere to be bigger than one person alone, so around 8-10 feet seemed like a good size to shoot for.

My first problem was trying to figure out how to model the pieces for the inflatable in the computer. I started by browsing fabric beachball patterns on craft websites like this one. I wasn't sure I could trust the downloadable patterns from sites like these at such a large scale and with non-stretchy fabric. I tried doing the math myself (given that the diameter = 9 feet), but got stymied on how to calculate the curve of the arc while also allowing at least 1 inch on all sides for seaming. I put out a message to the hive for some geometry support in return for free homemade pumpkin bread delivered to their office. I got two great responses:

1. Jennifer Jacobs calculated some curves for me based on a project that she had done where she needed to create an ellipsoidal form. Here's a link to her illustrator paths and her explanation.
2. Matt Hirsch sent me a helpful geometric solution to calculate the arc based on calculating the circumfrence at different latitudes of the sphere.
3. A third way of doing it that Jennifer and NovySan reminded me of would be to model a sphere in a CAD program like Rhino and then either use the Rhino uv unwrap function or else upload the model into Pepakura.