A complete redesign of RichRap's paste extruder. This design will work on a RepRapPro Huxley.See http://reprap.org/wiki/Mattroberts%27_Huxley_Paste_Extruder for detailed instructions on how to build.See http://richrap.blogspot.co.uk/2012/04/universal-paste-extruder-ceramic-food.html for hints on how to use.You probably want to use the replacement x-carriage ( http://www.thingiverse.com/thing:27901 ) to allow for repeated switching of printheads.Assuming you use a 200 steps/rev motor: steps per mm will be 765. This number is calculated in OpenSCAD - so if you change the gear ratios it will calculate the new value for you.