I created this long before the pencil cup contest, but I joined Printables just too late to enter that contest with this. 

I don't remember if I needed supports to keep the arch from failing, but the printing and assembly is a bit tricky. The arch is far too thin to print in parts and glue together, so print one side, then as the other side is printing lay the first side within the arch to interlock them and tape it to the bed so it won't shift around and cause problems.

I used braided fishing line as the string (https://www.amazon.com/gp/product/B009661Y72/). First thread it through the holes in the top of the arches and knot it off as shown in the pictures. Then tie a long length of line to one of the hooks on the top or bottom and work your way around. Wrap around each cleat once and really try to maintain a constant tension- if one side is tighter it will lean and if it's too tight it will bend. It will probably take you several tries to get it right but once you tie off the other end it stays pretty well. I've had mine on my desk in use for years.