What am I modeling?

I'm going to draw a 3D object for my final project. It will can put into a puzzle pieces and if the position will be correct something will happen. So this 3D pawns has to have a theme connected to the puzzle piece. I decided to make a standard pawns in wich it is possibile put into a thematic card. Therefore I designed two parts: one for the basement and one for the cover. Between this two parts there will be the card (Fig. 1).

Figure 1

The modeling: first Rhino then Free Cad

At first I decided to use Rhino (Fig. 2), but after one hour (when I had to draw the smooths to refine the pawns) I saw that "Fillet" command transformed the solids into faces, as you can see in Figure 3. I tried to solve this problem searching tutorials, but finally I decided to change software and to use Free Cad.

Figure 2

Figure 3

I had not problem using Free Cad: you can see the drawing actions and parameters in Figure from 4 to 12. The drawing is simple: some cylinders added and subtracted. The smooth using FreeCad is simpler than Rhino and after one or two hours I finished the 3D pawns and I could obtain the mold.

Figure 4

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Figure 12

Problem 1: Drawing the mold

I mistakenly subtracted the 3D I had shaped by a rectangular prism to get the mold (Fig. 13), but I realized there was a mistake because I could not understand how to put the connections to align the two parts of the mold and the cylinders to cast the resin (Fig. 14). So I created another rectangular prism from which I subtracted the wrong one.

Figure 13

Figure 14

Problem 2: Refining the mold

Understanding how to make the 3D model of the mold I managed to draw the connections for mold alignment, but since I was wrong to create the mold the first time, I did not think to preserve the edges to the prism so I designed the edges to get a box where the resin could be cast.(Fig. 14). I could make the edges more higher, but I decided to used a pieces of styrenefoam that I found at Opendot with the same dimensions as my mold.

Figure 15

You can show my STL design below.

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The milling machine

At Opendot I used the Roland MDX-40 machine and SRP Player software. I clamped a wood plate to the machine base and I fixed the styrenefoam to the wood plate using hot glue (Fig. 16).

Figure 16

Problem 3: The model was wrong

After finishing to prepare the file using SRP Player, I discovered an error. In some parts the endmill could not pass (Fig. 17) so I went back to Free Cad to increase the wrong distances (Fig. 18 and 19).

Figure 17

Figure 18

Figure 19

After exported the .stl file, I returned on SRP Player software and I followed all software step then you can see in the figures below:

I set up the dimensions of the model in Figure 20;

Figure 20

I selected the working of the surface in Figure 21;

Figure 21

I set up on the "Roughing" window the maximum size of the cutting in Figure 22 and 23,

Figure 22

Figure 23

the endmill in Figure 24 and the cutting parameters in Figure 25;

Figure 24

Figure 25

and I did the same on "Finishing" window following all the step (Fig. 26).

Figure 26

Then I chose the material setting Styrenefoam and I created the TooPath (Fig. 27).

Figure 27

The milling machine started to go the "Roughing" using a 3mm square endmill (Fig. 28) and then the "Finishing" using a 1,5 mm ball endmill (Fig. 29). The process lasted about three hours, but the result was very good (Fig. 30).

Figure 28

Figure 29

Figure 30

The casting phase

I used a two-component resin available in Opedot to create the mold. I calculated using 3D software that I needed 400 gr of white base component and 20 gr of blue thickener component. I mesured the two components through a weight scale and I blended them until the colors were mixed. It is important to mix slowly to avoid air balls. Finally I cast the resin inside the styrenefoam base dropping the compound from above so that any bubbles could break alone (Fig. 31). I repeated this process two time to have a better result. After two hours the polymerization was finished and I could separate the mold from the styrenefoam. You can see the mold in Figure 33.

Figure 31

Figure 32

Figure 33

Casting 1: Error with bubbles and material deformation

I used the acrilic plaster available at Opendot. The suggested dose was: 300ml of water and 1000mg of material. I mixed them carefully (Fig. 34) and then I used a gun to pour the material into the mold (Fig. 35). I made the casting two times because the first time there were some bubbles and the result was not good. Furthermore, the first time I closed the molds with tape and this deformed the pieces.

Figure 34

Figure 35

Casting 2: Good!

I made again the casting paying more attention and placing a rigid panel above and below to hold rigid the mold. After one hour I opened the mold and the second result was good (Fig. 36, 37, 38). I used sand paper to finish it across the joints.

Figure 36

Figure 37

Figure 38

Eventually I changed my final project but I decided to use my molded object with a different scope. You can find all my final project here.

Download area

Download my 3D file

Download my file for roughing the mold using Roland MDX-40

Download my file for finishing the mold using Roland MDX-40