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Machining is the process of removing material to revile the part that was living inside the raw material.

We use two different forms of material, cast/forge and “stock”. A cast item is an item that is formed to a particular shape that is further refined by the machining process. Stock is a standard shape that we then refine by the machining process.

Consider attempting to make an engine. The engine has many features within that have to be precisely machined, it also has many parts where “close counts” and other areas where it doesn’t matter at all. Plus, there are many voids. Places with no material.

Anything place that is void must have material removed. When machining an 80% lower, you must first drill some holes in the correct locations, then you have to remove all the material in the fire control pocket. As a forging, that pocket is filled with material that must be removed.

If it was a casting, then the rough outline of that pocket would be there. You would then use machining to remove the remainder to bring the pocket to dimension.

Same with an engine, same with many things. There are voids where we do not want any material. Using a casting allows for complex shapes and pre-placed voids.

So I’m going to talk about a chuck back.
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