## Saturday, October 16, 2010

### Volume Formulas 01

I'm starting to work on some mold making arithmetic. What I'm trying to figure out is how many cubic inches are in my mold box, and how many cubic inches my doll part is. I will subtract the cubic inches of my doll part from the cubic inches in my mold box to come up with an estimate of the volume of plaster I will need to mix. I use an arbitrary precision calculator called bc that allows me to assign values to variables.

l=4
w=3
h=2

v=l*w*h
v
24

A mold box that has the inside dimensions of 4 inches long, 3 inches wide, and 2 inches deep, is 24 cubic inches in volume. That can also be written as 24in^3, or 24cu.in..

For plaster molds that use coddles, the rectangular prism will be the volume used the most for the mold form. It is also a handy volume to figure out more complex forms that are being molded, since the more complex forms can usually be surround by a rectangle of some sort, and a height can be assigned to each rectangle.

pi=3.14
r=1.5

v=(4/3)*pi*r^3
v
14.12994

In the above formula, r is the radius of the sphere. If the sphere has a diameter of 3 inches, then the radius is one half the diameter, or 1.5 inches. pi is an infinite number that I have rounded off to 3.14. Pi actually looks more like 3.1415926.... The balls in ball-joints are usually spheres.

pi=3.14
r=0.75
h=4.5
v=pi*r^2*h
v
7.94812

Use the volume of a cylinder to estimate limbs, like arms and legs.