Metal casting in the sand requires a model to make a mold, which is usually an already existing object or a 3D print. After doing some tests with 3D printed objects, I was curious if I could skip the step of preparing a model and make a mold for casting directly on the sand. I had CNC milling technique in mind, but for the start, I tried hand engraving with a Dremel tool.
Step 1: Prepare the Sand
I pressed the sand in the box for casting, to fit two small models. With the first model I used the rounded tool, to get soft edges. Making the shape freehand was a bit difficult task, but didn't take a lot of time. The sand was not flying away as I was afraid it could do, and my other concern was what it does with the drill bits. With a model of this size, they were not damaged, but I would keep spare bits specifically for a project like this.
Step 2: Making Another Shape
With the second shape, I used the simple twist bit, to get closer to the CNC effect (the idea is still not doing it manually).
Step 3: Prepare for Casting
In the metal workshop, I collected pieces of aluminum and cut them in smaller parts to fit a can for melting.
Step 4: Pouring the Metal Into a Mold
I heated the aluminum with a torch and carefully poured it into the molds. It is also possible to make a 2-part mold with tunnels for pouring metal, to have a more precise outcome.
Step 5: Taking Objects Out
When the metal cools down a bit, it is safe to take it out with plyers and put into the cold water. The pot is still very hot. The leftover metal in it can be used for another cast.
Step 6: Cut and Polish
I used saw to separate the bottom part of a casted object (this is where the 2-part mold system works better!), but the round shape was not very easy for both the saw and the grinding machine, so I only minimized the edge of it. Then I used pads for polishing to make the surface more matt on the shiny areas, and a bit of sandpaper to fix some details of the casting. Of course, it is possible to do the opposite and give it a very shiny and polished look, but I liked the original roughness of it.
Step 7: Done
Here is the outcome, which can be developed into a more machine-controlled process.
I enjoyed working with the sand directly, without pre-making an object that I will probably not use again if I don't need another cast of it.