Fab Academy 2014

Jeff Opichka

Home                    Course Outline Project Management Project proposal Computer-aided design Computer-controlled cutting Electronic production 3D scanning and printing Electronics design Computer-controlled machining Embedded programming Molding and casting Input devices Composites Interface and application programming Mechanical design & machine design Output devices Networking and communications Applications and implications Invention, intellectual property, & income Project development Project Presentation I w

Molding and Casting My plan for the molding and casting unit was to design a FabLab logo, machine it out of machinable wax and cast it using plaster.  To start, I used Autodesk Inventor to design the logo using a block of wax that is 3 x 7 inches.   I would mill out a pocket 1/4 inch in depth leaving 1/4 of an inch on the outside wall so the plaster would not run off the edges.  The text and logo would be inside the pocket and be milled 1/4 of an inch below the pocket.   When finished designing in Inventor, I found it very easy to import the part into MasterCam.  Once in MasterCam,  my letters seemed to be a bit complex so I made a few changes as you can see in the second image.  Creating the G code and machining went very smooth.  I proceeded to mix the plaster and cast the mold as you can see from the images below.    I let the plaster cure for 24 hours before I attempted to work with it.  I new there was a problem when I went to take the cast out of the mold.  Tapping on the mold with a hammer and prying using a screw driver still would not release the cast from the mold.  Only after breaking off chunks of plaster would the cast come out while only saving a small chunk of logo.  There were several lessons learned from this first cast.  First, letters or graphic can not be 90 degrees to the mold, a slight chamfer helps the cast seperate from the mold.  Second, creating the pocket for the plaster to settle creates a bigger head ache when trying to take out the cast.  Third, a release agent prevents the plaster from sticking to the mold.   I went back to MasterCam and made a few changes.  Instead of using an end mill I used a 90 degree engraving bit so the logo and letters would come out of the mold easier.  I eliminated the 1/4 inch pocket and created a tempary box around the wax using cardboard and duck tape.  I coated the entire mold with dish soap before poring.  As you can see from the images below the cast did work.