Rhino3D has a powerful programming language; Grasshopper. This is a Grasshopper programme to generate moulds from any design. There is a video to show how it works.

UPDATE 8.9.15: Grasshopper programme updated to reflect updates to Grasshopper versions since first published. Please remember to install Hoopsnake for Grasshopper too!

This is ONLY going to be useful to you if you have access to Rhino3D version 5 or later.

There is a downloadable Grasshopper programme file and a demo file with a design and a spare. (Where you pour in your mould material). The output of the programme generates a MASTER mould. There are lots of customisation options - many of which you can see in the video. There are also plainly labelled tweaks within the programme for all manner of things; shell widths and slopes, bi-material offsets and interface configuration and much, much more.

A typical use is to create a plaster master mould. Clay slip is then poured into the resulting plaster mould to generate a slip cast version of your design. The design of course has to be castable...

Video available at http://youtu.be/3kU9nRV_ObA

FEEDBACK APPRECIATED. Do always download the latest dated Grasshopper file!

UPDATE 18.1.13: Also added selection for standard (rather than master mould) generation. So now you can also use the moulds for casting outputs directly.

UPDATE 19.1.13: Platform base now scales to absolute standard thicknesses so you can use a base-board to extend the width of open platform master moulds. The bi-material platform now has a central print-through of the top material to ensure its extruder remains functional through the print. This version of the programme requires HOOPSNAKE, as the base thickness calculation now has to iterate to get the right value.

UPDATE 20.1.13: Removed previous update; it works fine but you need to manually trigger the Hoopsnake iterations when the programme is first loaded. This update auto-triggers Hoopsnake to ensure iterative absolute platform scaling works without intervention from programme load.

UPDATE 22.1.13: Added optional user defined cutting plane. Previous XZ cutting plane assumed to be geometric center of design in XY plane. Fine for symmetric designs but not for designs with Y axis assymetry. Also added error status reporting so you can hunt down Rhino solid operations errors. (And Hoopsnake's arbitrary tendency to stall now and then)

UPDATE 24.1.13: Finally found a feedback mechanism to trigger Hoopsnake refreshes. Also moved mould perimeter offset to be more visible as it turns out in the real world, the ceramists need to tweak this to get the right master mould width for slip casting.