Xin Wen

How to Make (almost) Anything

Week 8: Molding and Casting

cake making comes in handy

1. 3D Design a Positive Mold
2. Machining the Positive Mold with Machinable Wax
3. Casting a Negative Mold with OOMOO
4s. Casting a Positive Object with Drystone

This week's assignment is to read datasheet of the material we are going to use, make a 3D mold, machine it, and use it to cast. The basic workflow is:

  • design a 3D positivemold
  • machine it out of wax on a cnc mill
  • cast a negative mold with the wax mold(we used OOMOO)
  • cast the final product in the negative mold

Tools/material used: Rhino for modeling, Cut3D for generating tool path for the cnc mill, CNC Shark for milling, machinable wax, OOMOO, Drystone

1. 3D Design a Positive Mold

Figure 1. My inspiration for this week: artist Xu Bing's Square Wall Caligraphy.
Figure 2. My name in English Spelling written as a Chinese character.

2. Machining the Positive Mold with Machinable Wax
Figure 3. Left: preview of rough tool path; right: preview of finishing tool path.
Figure 4. Left: zeroing xy axis; right: zeroing z axis.
Figure 5. From left to right: the block moved in the middle of milling (you can see the two holes on the edges); the feedrate was too high so wax melted onto the flute, resulting in rough finish; I used a flathead screw and heatgun to smooth the surface; after clean up.
3. Casting a Negative Mold with OOMOO

Figure 6. From left to right: preparing oomoo; pouring it into the wax mold; first OOMOO negative mold (you can see part of it was missing because of bubbles).

To get rid of the bubbles, be careful not to introduce air into the mixture when you mix. Some people recommend mix part A and part B in the first cup for 2 minutes and pour the mixture into a second cup slowly so that the bubbles burst when they pass the edge of the cup. When you pour into the mold, pour into one place and let the mixture flow itself to avoid introducing air. Then you can shake/tap on the mold so bubbles get to surface like how you make cake batter. You can also put the mold into a vacuum chamber to degas the mixture.

Figure 7. From left to right: casting another oomoo mold; the wax mold broke when I tried to take oomoo out; second OOMOO mold
4. Casting a Positive Object with Drystone
Figure 8. From left to right: I enclosed the sides with cardboard to give the final cast more thickness; instructions on the drystone powder; poured mixture into the mold!
Figure 9. Left: solidified cast; final object!
Figure 10. Family Portrait!