The approximate weight of the amount of metal in a casting can be calculated from the weight of the pattern.
The calculation of casting weights is important in the operation of any foundry, even in the hobby foundry. And for that reason, some information on the methods and practices used is given.
If you have on hand a casting that is to be replicated, then it is only natural that this casting can be weighed, but there is extra metal consumed with the gates runners and risers, so allowance for these should be included.
It is obviously quite simple to calculate the weight required to pour a casting if it is on hand. Since risers and gates are usually round (and should be) in their cross section, it is easy to calculate their weight and add it to the weight of the casting.
Pine and mahogany timber have a greater density and a lower factor must be used to calculate the casting weights.
Where neither of these methods is possible, it is necessary to break down the design into simple sections, such as rounds, squares, and plates, and calculate the weight of each section by determining its volume in cubic inches, multiplying this figure by the following weights per cubic inch below, and then obtaining the total:
Pounds Per Cubic Inch.
Cast steel: X 0.284.
Aluminum: X 0.098.
Cast iron: X 0.260.
Bear in mind that for the hobby foundry, it is not compolsery to calculate how much metal is required, mostly one will ere on the generous side, and if there is metal left after the pour, it can be simply poured into the ingot mould, and melted again at a later date.