I noticed with my old design ( http://www.thingiverse.com/thing:426492) that the curved bottom edges of the printrbot simple metal were causing the feet to gradually slide towards the middle of the printer making it less stable and eliminating the point of the feet.
This design is made to eliminate that problem by having slots for both sheets of metal at a corner, making them practically immovable.
I hope you guys like it.
PS- This design also includes holes in the bottom for rubber pads. I included the Solidworks .sldprt files so that you can customize these holes and any other aspects of the design to fit your needs.
Print two of each file. the depths of the cut are customized in each to fit either the front right and back left or the front left and back right. This is due to the way the metal sheets meet up on the printrbot. If you print two of each file it should be obvious where each fits best. If you have questions feel free to comment.