by milligan, published
Runners, channels and sprew basin for sand casting. I can make a sprew if requesed. Edit: SketchUp files have been added. Edit: slight changes to the runner, stl files added (after they were accidentally deleted)
You can scale this to the size of your casting, but make sure to scale all of the parts. Only one part per runner is recommended. Use a .75 inch diameter (on the narrow end) sprew.