Tuesday, October 18, 2011

How much resin? (Math Heavy)

Smooth-Cast 300
Mix Ratio by Volume = 1A:1B
Mix Ratio by Weight =  100A:90B
Specific Volume = 26.4 cu.in per pound

Goal
Find out how much resin I need either by volume or weight that can be easily mixed.

Volume to Weight Conversion of Materials
1 cu.in. of Van Aken Modeling Clay (which is the oil clay I use) weighs 30.9 grams.
1 cu.in. of my Carving Wax weighs 25.3 grams.

To get these numbers, I just made a cube that was 1" all around and weighed it.  Of course these numbers are just rough estimates.

The head used to make the 4-part mold weighs 23.6 grams.  The head is mostly Carving Wax, but also has some oil clay.



If the head was pure oil clay, I would need 0.76 cu.in. of resin.
Volume of resin = Weight of sculpt in grams / Weight of 1 cu.in. of oil clay
Volume of resin = 23.6/30.9 = 0.76

If the head was pure carving wax, I would need 0.93 cu.in. of resin.
Volume of resin = Weight of sculpt in grams / Weight of 1 cu.in. of carving wax
Volume of resin = 23.6/25.3 = 0.93

If you notice I would need less resin if the head was made of oil clay than if it was made of carving wax.  The head is mostly carving wax, so I have decided to just go with assuming it is pure carving wax.  I will also round up and say the head was 1 cu.in.

Amount of resin needed is:  1 cu.in. (which is volume)

Is that easily measured out?  No.  So I will convert to measuring by weight.

If a pound of resin is 26.4 cu.in.  So 1 cu.in. of resin would weigh 0.61 oz.
1 cu.in. of resin = 1 (lb) / 26.4 = 16 (oz) / 26.4 = 0.61 oz.

So if the head is 1 cu.in. and 1 cu.in. of resin weighs 0.61 oz.  Then it is safe to say I need 0.61 oz of resin for the head cast.

So now I need to figure out how much of A and B I need.  The ratio is 100A:90B.
Part A = (1.65 / (A+B)) * A = 0.61 / 190 * 100 = 0.32 oz.
Part B = (1.65 / (A+B)) * B = 0.61 / 190 * 90 = 0.29 oz

So, how much resin do I need by weight?
0.32 oz A : 0.29 oz B
-or-
9.07 g A : 8.22 g B

But because there are vents and the pour gate to consider, I will increase the amount by 10%.

So using grams, I would need 9.98g A and 9.04g B.  Lets just round it up to 10g A and 9g B for a total of 19g of resin.

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