Assignment
Design a 3D mold, machine it, and cast parts from it.

For this week assignment I decided to make a key-ring.

1.- Create a positive mold model

I made the model in Rhino and exported it as a .stl file to milling the wax on the Modela.

2.- Mill the wax on the Modella

To milling the wax on the Modela you need to make two cuts, a rough cut for the general shape and a finishing cut for finishing it.

I used a 3 mm bit but I did not review the tool path before the start of the cut, so I didn’t realize that the bit was too big to mill the engraved text until the Modela finished the work.
 
LESSON LEARNED: Review the tool path before start the cut.

I modified the model in Rhino, using a different font for the text and a different deep for the engraving text

This time I used a 2mm bit for the rough cut and a 3 mm bit for the finishing cut.

I used these settings in the Modela

Rough cut general settings:

- Bit diameter 2 mm
- Overlap 0.25
- Offsets -1
- Speed 20 mm/s

Rough cut 3D settings:

- Select xy path
- Top intensity 1
- Top height -1
- Bottom intensity 0
- Bottom height -30 mm (the height of my model)
- Cut depth 0.75

After the rough cut

Finishing cut general settings:

- Bit diameter 3 mm
- Overlap 0.75
- Offsets 1
- Speed 20 mm/s

Finishing cut 3D settings:

- Select xz and yz finish
- Top intensity 1
- Top height -1
- Bottom intensity 0
- Bottom height -30 mm (the height of my model)
- Cut depth 0.75

After the finishing cut

3.- Make a mold from the wax

I used PMC 121-30 Dry to make the negative mold.

There are two important issues to consider when you work with PMC 121-30:

- You must Pre Mix the Part B before using.  After dispensing equal amounts of Parts A and B into the mixing container, mix thoroughly for at least 3 minutes making sure that you scrape the sides and bottom of the mixing container several times.

- You must use a 1:1 mix ratio by volume or by weight

Here is the negative mold after a 16 hours curing process.

4.- Cast the final object

I used Smooth-Cast 300 liquid plastic.
It has a 10 minute demold time.
It has a 1:1 mix ratio by volume and a 100A:90B  mix ratio by weight.

Here is the final cast

Final files:
llavero1.stl
llavero2.stl