Week 9: Molding and Casting

Concept

Right now it is the most beautiful time of year in New England.. FALL. Beautiful leaves everywhere. Inspired by this, I wanted to make a bowl with an imprint of a leaf. I simply wanted to make an object with a very naturalistic figure (real-looking leaf), set within a sculpted, platonic form. To do this, I would need a 2-part mold: the plantoic "bowl" and the imprint of the leaf. In my mold design, put 12 registration dots around both molds, so they could be combined in different ways. Also, I designed the bowl to sit slightly askew. With a flexible rubber mold, I could cast a set of them with each slightly different leaf to bowl orientations.

Design

Then I had to traslate that into Rhino. This was VERY complicated... There wasn't a way to simply tell the computer: Average out these trangles to make bigger triangles out of them. I would have liked to arrive at a triangulated abstration of the 3d scans of these leaves (essentially that is what 3d scanning does anyway) so I tried to do that by hand, using the surface command in Rhino:

Yikes. That looks ugly.
So instead, I used the Drape tool to drape a surface over this super-complex leaf mesh, and then did a bunch of 2d projections and some curve editing to arrive at a surface-leaf:

Then I lofted the curve of the leaf to the plane of the mold. Final mold design, to be exported as .stl:

I am not entirely satisfied with this design. It looks like a leaf was pushed through some mud. Chris suggested using the greyscale value to interpolate the depth in Rhino, and Matt mentioned the Minolta 3D scanner may give me more control to start with a simpler leaf scan. I am open to suggestions!

Milling

Back to the ShopBot! I hot-glued the piece of purple wax onto a scrap piece of wood, which was then screwed onto the sacrificial layer. Using the ShopBot's software, I created Rough Cut and Finishing cut toolpaths:
Rough Cut: 6 min: 1/4" ball nose bit, 9000rmp, 2 in/sec
Finishing Cut: 23 min: 1/8" ball nose bit, 12000rpm, 2 in/sec, and 15% stepover
Rough Cutting:

Finished Wax Mold:

The cuts show lines, but in the interest of time I opted to skip the 90 degree turn 2nd cut.

Casting

I used the flexible rubber PMC 121/30 DRY-- mixed well, pour in thin stream, tap out air bubbles. And I stuck the two molds in the convection oven for an hour at 175 degrees F.

Here's what came out:

Then I cast it in hydrostone:

Final Product