Sand casting is a great technique to duplicate parts fast in metals with low melting points. This method can be used for making a quality prototype duplicate. When done properly a good range of detail is possible. You can do this easily at home although it is advised to do this in a workplace, since the sand can make things messy. All parts are easy to find, except for the silica sand. But search the internet and you should be able to order the needed amount for a low price.
Step 1: Gattering Materials
The tools and components you need will be:
- The object you want to duplicate. The range of detail which you will be able to archieve is dependable on what material you use to make the duplicate with. We used two parts which makes it easier but is not required. Undercuts are impossible as well since you'll need to take out the original part mid process.
- Tin or another metal with a low melting point. We used tin from old plates picked up at a second hand shop.
- Silica sand (sand with a clay component)
- Flour, used for garanteeing the two parts of the casting box not sticking together.
- A casting box made out of two parts with guides for a good connection (you can make this in whatever you have laying around, the most important thing is that it is strong enough to withstand the outward pressure when the sand is rammed in the box).
- A fine straw or long toothpick for making ventilation holes.
- Stamper for pressing the sand down in the box. This can be made of anything but must have a flat surface.
- Cilindrical object. This is used for establishing the pouring hole.
- Heating element for heating the metal.
- A brush or air compressor to get rid of sand still on the object.
- A belt sander or regular sandpaper.
Tip: make sure the sand is as dry as possible. Doing this in a humid environment will make the process a lot more difficult.
Tip: Do this on a flat surface to make sure you have a smooth surface of sand when casting.
Tip: Do this outside or in a workspace. If not done properly, the sand could fall out and make a mess.
Step 2: Pouring the First Casting Box-part
- Position your part in the first box (the one without guides). Make sure not to put the object too close to the edge.
- Pour over the sand. Make sure you fill the box as much as you can, preferably to the top.
- Stamp the sand down with a flat surface.
- Flip the box over (the sand should stick together nicely) but careful, it is possible sand comes out if not stamped down properly.
Step 3: Pouring the Second Casting Box on Top of the First
- Before you mount the second box, straw some flour over the surface already in the first box.
- Put the second box on top, the guides should make sure of a snug fit.
(- Mount the second part of the piece on top. This step is optional, if you use just one whole piece. You can ignore this.)
- Put in the cilindrical object. Make sure you put it about two centimeters (or an inch) away from the part.
- Pour sand in the second casting box.
- If you filled the first box completely you can now use the stamper to press down the sand in the second box as well. The two casting boxes won't stick together with flour between them.
Step 4: Preparing the Sand Mould for Casting
- First remove the cilindrical object out of the top box.
- Take of the top part carefully. When the sand is pressed down properly it should come of without the sand braking away.
- Use a toothpick or fine object to take out the original parts.
- Use the toothpick or fine object to poke wholes through the sandmould top box (NOT THE BOTTOM BOX). This will make sure air can get away when pouring the metal in.
Tip: poke wholes in the deepest cavities of the negative. This will allow all air to be forced out.
- Use the toothpick or fine object again to make one or more spruepoints (half a centimeter or quarter inch wide) connecting the negative to the cilindrical hole.
Tip: When taking out the part, making the airflow holes or the spruepoints some sand might come loose. Make sure you blow this away. It will make a small extra cavity that will fill up with metal as well. But can be sanded down afterwards.
Step 5: Casting
- Put the top box again on the bottom one. When looking down the cilindrical hole you'll see the spruepoints you just made.
- Heat up your material.
- When the material is fully liquid, pour it in the cilindrical hole.
- Make sure the cilinder is fulled up as well, it will provide more downwards force which will force the material in small cavities.
- Let is rest for an appropriate amount of time, this is dependable on the used material. For tin we waited about 20 minutes.
- When the metal is turned fully solid, take of the top box off once more. Lift the boxes a bit from the working surface and press down with your hand or a hammer in the sand. The sand and rough duplicate should fall out if enough pressure is applied.
Tip: you can use the same sand for about 4 times so make sure you gather it back up and store it away for later use.
Step 6: Finishing Up
- Try to pry of the cilinder. If your spruepoints were deep you will probably need pliers.
- Brush or blow down the duplicate. Make sure no sand is left on the duplicate.
- Use the beltsander to get rid of the airventing hole points. If you don't have a belt sander, use pliers.
- Sand the duplicate and polish it up.
- Add the needed parts, in case of a catapult: an elastic band and keychain ring.
All done, you made it!