The document discusses the process of molding and casting, including designing a mold by splitting or rotating the 3D model to avoid undercuts, carving the mold in wax using a CNC milling machine, and making mistakes like using a mill that was too large which required manual repair. It also describes making the mold with silicone rubber in different techniques, and casting copies with urethane resin that came out successfully despite problems with the mold.

1. MOLDING & CASTING
SAVERIO SILLI

2. MAKINGAMOLDWITHMACHINABLEWAX
MY FIRST ATTEMPT AT
AND ALL THE ERRORS I MADE
fabacademy.org/archives/2015/eu/students/silli.saverio/exercise09.html

3. DESIGNING A MOLD
Your 3D model resembles what your final product will be,
but in order to make it machinable as a mold, and for the
mold to be working, you need to modify it.

4. DESIGNING A MOLD
By splitting the model or rotating parts you can achieve a
shape that has no undercuts or that is symmetrical (meaning
you can make only one rubber mold and cast twice).

5. DESIGNING A MOLD
In the same block of wax you can carve more than one mold. In
this case we’ll have a one-valve mold on the left and a two valve
mold on the right (notice registration keys are symmetrical).

6. CARVING THE MOLD IN WAX
The wax block is secured to your CNC milling machine (in
this case, a Shopbot) with wooden sticks and double-sided
tape underneath.

7. CARVING THE MOLD IN WAX
Rough-cut path (6mm end-mill) and cutting results. As you
can see on the right, the mill was too large to pass between
the part and the mold walls, resulting in a lot of material not
being removed in the rough-cut step…

8. CARVING THE MOLD IN WAX - TROUBLES
Having all that wax not being removed during roughing-cut
resulted in the 3mm ball-nose mill used for finishing, to crack
just at the beginning of the finishing-cut. TIP: Design your
mold having in mind what size your mills are going to be.

9. CARVING THE MOLD IN WAX - RESULTS
The final result shows a misalignment due to the incident
with the milling bit. Also the registration keys didn’t came out
good. A lot of manual work was needed to adjust this mold.
An attempt at using a flame to smooth the surface resulted in
melting one wall tath was too thin (on the left).

10. MAKING THE MOLD WITH SILICONE RUBBER
The two valves side of the mold was made with a “brush on”
technique, in which you only apply a layer of rubber of a
couple of mm on the mold. When the rubber hardens you
pour some stiff material like gypsum to make an armor that
holds the soft rubber. The other side of the mold is just poured
silicon rubber (notice the walls had to be risen with tape).

11. CASTING WITH URETHANE RESIN
The two valves were framed in two wooden boxes to make
the mold easier to close (it was used for rotational casting).
The one valve part came out pretty good. Despite all the
problems I had on the mold all the copies came out good.