Parametric Apron for Reducing Warp

While printing the various large z axis components, I was struggling with significant warping. Stopping the corners of the bits from cooling quickly seems to help a lot (see picture). So I knocked up a parametric version of the magic corner pieces to help me (and you) with the problem in the future.

inspired by http://hydraraptor.blogspot.com/2010/09/some-corners-like-it-hot.html , which may have been inspired by http://technocraticanarchist.blogspot.com/2009/12/printing-big-bits-of-mendel.