Cup Holder for a Porch Swing

Another one of those start-of-Summer rituals is getting the old porch swing back into working shape. Ok, we don't actually have a porch; the swing really is on our deck right now and we'll be moving it to near our pond, but that's irrelevant.... Anyway, what good is a swing if you can't enjoy a refreshing beverage while swinging? Here's my cup holder that clamps onto the non-swinging metal sidebar of the swing.

See http://www.thingiverse.com/thing:347495 for the improved double-cup holder....