Oh , Dear , a pattern is what you use to form the mould for a casting .
The principle is that you make the shape of the thing in wood , then use that to make a mould by putting it into a box and ramming a mixture of sand and binders around it . You then split the mould , remove the pattern and reassemble the mould . You then pour the molten metal into the space in the mould . When it has cooled you extract the cast object from the mould , and machine it to make what you want .
For good pictures of patterns and castings look at Little Samson's posts .
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