Basic Resin casting, Illustrated - Two part silicon : Two part mold

Hjholter3

New Member
Recently I was building a Revell 1/72 Tiger 1 when I lost the outer half of the drive sprocket to the carpet monster.



After seeing the damage I was forced to think "Now WHAT?" and it occurred to me that I could cast another from the surviving
Drive sprocket on the other side.

dr04.jpg


bzs5.jpg


As you can see a simple one piece mold would not capture the detail on the back of the sprocket nor the form.

To replicate the part I would need, I would need to make a two part mold, and use silicon to make the mold itself.

In this tutorial I decided I would use a different brand for the Molding Silicon - While I normally use Alumilite products I wanted to show that the techniques I'm using are applicable to a vast number of brands, as long as the product used was 1:1 mix.


1. Two part 1:1 Silicon putty

2. 1/2 TSP (2.5 ml) metal measuring spoon
3. Alumilite Amazing two part casting resin
4. Clear "Condiment" Cup
5. Small plastic straw ( a Capri-sun Straw )
6. Vaseline 100% Petroleum jelly 2.5 oz tube
7. Driver sprocket, outer, Revell 1/72 Tiger 1


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This is the Silicone putty I'm using for this tutorial. I got it on eBay, shipped for 10.95 but your mileage may vary. According to the ranger ink site, it sets in 7-10 minutes.

Step one: Prepare molding silicon
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The Molding putty is 1:1, so I estimated double the 1/2 tsp would be enough for the "bottom" of my mold. I actually ended up with enough for two 1 1/4 inch diameter by 1/8th thick molds - so for this part half would have been perfect, but hind site is 20/20..
Anyway, I filled the Teaspoon with part A and part B separately and then Kneaded them together until they where a nice homogeneous gray. I then made a pad of putty approximatlely one nad one quarter inch in diameter - using the pattern object as a guide - I wanted at least a full centimeter of putty on all sides of the pattern object, but less is indeed possible.
Step Two: Make the Mold
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After The molding putty is prepared, I pressed the good sprocket half into the surface until most of the object is below the surface- This makes it possible to use less putty for the "top" of the mold. To insure the "top" and "bottom" of the mold press together I used a LEGO single block to press round + square indentations into the "bottom" of the mold. After the putty has cured, I Brushed a thin layer of Vaseline onto the pattern object and upper surface of the mold.
Step Three: Encapsulate the Pattern and complete the mold

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At this point we prepare more molding putty ( I made about an eighth of the original amount ) and press the putty into the top of the mold and encapsulate the pattern object. to create a place to "Pour" the resin, I cleaned the putty away from the "back" of the pattern object where it mates to the inner sprocket. In the image above you can see the two halves minus the pattern object, after everything has cured and is ready for resin.
Step 4: Mix resin and pour
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As before, I'm using two part Alumilite "Amazing" casting resin. Using my 1/4 teaspoon, with a mark at the half point, I measure equal parts of both and mix in my condiment cup. After the mix, I use my Capri-sun straw to fill what will be the "front" of the sprocket, and then press the top of the mold on and fill the "back"
Step 5: Allow resin to cure, and demold!
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I pulled the "top" of the mold off to reveal this beauty. With a bit of machining she'll be ready to go.
 
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