For our Final, the project was milling a 3D object using the CNC machine, mold it and then cast new objects from it.
To complement out last assignment, me and Lucas decided to make the power-star from Mario and finish the class in an “invincible” way!
This was a very complex project. To fully describe the whole process to complete it, we decided to break it down into the differnt steps we followed.
- Finding the 3D file and preparing the G-code;
- CNC milling;
- Molding;
- Casting.
- Finding the 3D file and preparing the G-code:
(i) Finding the 3D file: In order to find the best file possible, we searched the power-star on Thingiverse and we found a star that was already split in two:
Using solid works and some radial symmetry, we were able to hide the hole and obtain a solid star. After that, we created a rectangular base under it and imported the file to Fusion 360.
(ii) Preparing the G-code:
On the Fusion 360 software we were able to create the tool-path that the CNC machine would use to mill the power-star. We created the G-code using two different operations: 3D clearing and morphed spiral. The first one is a rougher cut with a step down of 3mm, used to remove all the extra machinable wax. The second one is a finer cut with a step over of 1mm, used to obtain a smoother and more detailed surface.
2. CNC milling:
The CNC milling was a very complicated part… Now we are gonna describe the problems and the solutions we used:
a) Coolant problem: When we imported the G-code to the FlashCut software to perform the cut, we had a problem with the coolant commands. For every start and end of operation, Fusion 360 writes one command to turn on or off the milling coolant. Since our CNC machine does not have a coolant mechanism it did not recognize the command. To fix it we opened the G-code and manually deleted all the lines corresponding to coolant commands, that means lines containing M7, M8 and M9;
b) Origin problem: At the start of the code, Fusion 360 writes the command G54 to offset the origin of the model with respect to the machine origin. This caused the start point of the program to be off the position we set in the FlashCut software. In order to solve that, we deleted all the line having this command;
c) “Error code 1004”: This is probably a glitch in the FlashCut software, for some reason this software was reporting an error in every G3 command, for no reason. To solve it we turned off the time prediction check box in the software and the error disappeared. This way we didn’t know how much time the milling would take, but it works.
After we fixed all the problems, we successfully were able mill the front and the back of the power-stars. Each part took approximately 2 hours to complete.
3. Molding:
After post-precessing the power-star, we were able to use the Oomoo to create two molds, one for the front and the other for the back part. This was by far the simplest part, and we didn’t have bigger issues with it.
After 2 hours of pouring the oomoo, we obtained 2 very good quality molds:
4. Casting
The next step was to cast the stars out of the of molds. To do so we used the Smooth-Cast 300 for the solid color power-stars and the Smooth-Cast 325 for the amber ones. We also used some yellow colorant.
The biggest problem with had with the liquid plastic was the time it takes to cure. It is a very exothermic and fast reaction. On our first trial the mixture cured while we were still pouring it. After a couple trials we were able to figure out how to use the liquid plastic.
We realized that making a 2 part mold wasn’t a good idea because the stars could end up not concentric, and look aesthetically bad. Therefore, we decided to make 2 individual 1 part molds. The problem we had now was on how to glue the 2 parts of the power-star together. We fixed this problem by making the front of the power-star and, once it is completely cured, we drop it over the back part of the power-star while it is still liquid inside the mold. This is result after gluing:
It has a very smooth finishing and we were very proud of the result!
The final step we took in order to finish the star was painting the eyes using a black sharpie. This is the final result:
We are very proud of our power-star! It has a very smooth and high quality finishing.
Our only complaint it that the plastic gets dirty very easily. But thats a characteristic of the material, you just have to handle it carefully.
I hope you have like our final power-star and all of our other projects!
“-Mario clear!”
