Design appropriate objects within the limitations of 3 axis machining
Demonstrate workflows used in mould design, construction and casting
This week I decided to make a mould that consists of two parts, the top and the bottom, which I will close together and get a Light Bulb. As simple as that!)
The idea is to make a double sided cast, which will have two parts different from each other, and also keep the design simple.
I decided to cheat a bit at my design, and downloaded a picture of a light bulb from internet. I inserted the picture as a reference in Fusion 360, and using
spline line, I started drawing on top of the picture.
After I have half of the bulb ready, I use the
revolve tool to give my sketch a dimension. This command revolves the sketch at a certain angle which can be specified. In my case, I need a full rotation of 360 deg.
I also draw a rectangle with the dimensions of my wax block,
width: 142mm/ Depth: 92mm / Height: 36mm and extrude it. I should get a 3D mobel of a light bulb and the wax block in order to operate with them later
Now I have to place my light bulb on the wax piece, or inside it to be more precise. I draw a bigger rectangle in the place where the bulb will be, and cut it through at a depth of a little bit bigger than the dimension of half of my bulb. Using the
Align command, I select the middle point of the bulb and then the point at the center of the new rectangle, and now the two bodies should be aligned.
I could just copy the bodies, and have the two pieces which I need, but that would be too easy, isn't it? :D
In order to make the two pieces differ from each other, I want to write something on top of it. As I had lack of creativity at the point when I was designing it :D, I made the most typical FabLab on top of the first piece, and LED on the other half
To align the writings with the bulb was a bit tricky, but after I watched some tutorials about How to write something on a curved surface, I was ready to proceed. First, I create a sketch with the text I want, and extrude it, but not to
Distance but select
To Object, and specify the surface of the bulb as the desired object
Now I select the new bodies (the letters), and move them by
2mm inside my bulb.
At this point I make a
boolean substraction using the
Combine tool, specify the bodies, and select the
Cut operation. This is what I get:
Now it looks more like an engraving inside the bulb, but I want the letters to be slightly out. To do that I use the
Push / Pull tool, select the faces of the letters, and pull them by
3mm. And I get the result which I wanted!
Later I realized that the letters are too small for the CNC tool to go inside, so I changed it just to FAB.
I repeated the same process for the other half where I wrote LED
Now its time for the CAM process
I used the Fusion 360 CAM processor, which is very powerful in my opinion and easy to use. On the left panel, I switch from
CAM, and create a new
I specify the X,Y,Z coordinates, and place it in the exact same way as I place it in the CNC machine (bottom left corner in my case)!
In the next
Stock menu I choose
Relative size which means the real size of my design, and set all the offsets to zero
To mill the model, I decided to make three jobs, one
rough cut, and two
finishing cuts. I do 3 jobs because I want to get the maximum out of the CNC machine, but it is also possible to have a good result using just one, or two jobs
To make the first job, the rough cut, I click on 3D, then choose
Adaptive clearing, and in the appearing menu, I choose the tool which I want to use. I will be using the
6mm tool. I measure all the dimensions of the drill tip, and introduce it in the library
Here are the parameters which I used for the rough cut, the most important ones I marked with color
A very good advice is to always simulate the toolpath before milling. It could save the future effort, and could avoid making mistakes in the real process. The most important parameter here is
Colisions: none, which means I am safe to launch the job!
In the Post Process I have to specify the CNC machine which I am using, in my case its Roland MDX40. Choose the right settings, and generate the
The last settings on the machine, I open VPanel, and after I fixed the wax block inside the machine, I find the XYZ axis and launch the job by inserting the generated .gcode!
For the finishing cut, I used almost the same procedure, except the parameters are slightly different. The tool I was using is
flat end 2mm
This time I did not select Adaptive Clearing, but a Parallel job. These are the tool dimensions:
These are the only settings which I changed:
For the last finishing cut, I wanted to go super smooth! Because the smallest tool available in our FabLab is 2mm, I used the
2mm ball end which must suit better for the smoothing of the curved surfaces.
To apply the settings only for the bulb, I selected the option Avoid touching surfaces and selected all the faces except the one I want to smooth, the bulb!
These are the settings I used for the last job! I decreased the spindle speed, as well as the cutting feedrate in order that the wax does not melt. And the most important parameter is
Stepover = 0.2mm. This is the key parameter in my opinion, which gives that crazy smoothness that I am looking for
Here is a nice comparison between the different jobs, the rough cut, and two finishing cuts:
This is the final model:
Unfortunately, I can still see the tool paths, but I think this is due to the material properties. The wax maybe is too soft, and leaves traces. Anyway, the model is really smooth, and I am satisfied with the result!
In parallel I also wanted to make a comparison between two machines, CNC and 3D Printer, to see which one will output a better result
I did not go to cast this mould because it is obvious that the 3D printer loses in precision comparing to the CNC machine
Let's cast it!
First, I have to make the mold out of silicon rubber. The one we are using here is
Protosil RTV 245 silicone. Description about how to use it can be found Here
After mixing the silicon with the hardener following the mixing ratio stated in the datasheet, we placed it in the Vacuum Machine! We left it there for several minutes, until the air bubbles came out, and then poured it into the wax mould. I also fixed the two pieces together using wood, and also increased the height of the mould
The important thing is to make it slowly, and from a fixed position, center of the bulb in my case, in a way that the fluid can reach all the corners and holes. After I covered both moulds, I keep pouring to increase the thicknes of the future silicon mould
After I covered it enough, I placed it again in the vacuum machine for about 20 min. After that, I left it dry overnight!
The next morning, I removed the silicon, and this is what I get:
Now the Sticky part begins :D
The resin which I decided to use is called
NEUKADUR ProtoAmid 60, the datasheet can be found Here
I chose this resin because its transparent! While I was making the mould, a great idea came to my mind! I want to place a RGB LED inside the cast, and make a real lamp out of my light bulb!
I prepared it in advance, soldered the 220ohm resistors to the necessary pins, as well as connected the pins with cables, and isolated everything using the shrink tubes
I followed all the instructions from the datasheet, but to be honest, I managed to properly cast my piece only from the third try.
The problem was the pot life of the chemical mixture which is only 4 min. Twice I tried to cast, but the resin got hard, and I was not able to pour it inside my mould.
From the third try, it looked better more or less, but still I had a feeling that something went wrong. I left my piece for the night, and in the morning this is what I got:
I know, looks like shit :D
But I am a stubborn guy who never gives up! For the fourth try I asked for help)
The God of Casting was guiding me, and he advised to use a different resin, which is more transparent and has properties more suitable for my goal. This is the one that we used: NEUKADUR ProtoCast 195, the datasheet Here
After a quick tutorial on moulding and casting, we prepared everything, and I was surprised how professional it looks!) Here is a short video of the mixing process in the vacuum machine
And guess what?! The result was amazing
I was really impresed by the quality, so smooth, so transparent, wonderful!
I did not have a RGB Led this time, since I ruined the first one, so I casted it without.
In conclusion I would like to say that it was a great experience. YES, I failed three times, but I still managed to do it the fourth time.
Moulding & Casting really opened a new world for me, new opportunities. Everything around us is made using this technique, and having the knowledge to create things, feels AMAZING!