upon the steel grade, the difference in final cost between an extrusion
and a part made by machining can be enlightening. Look at the part
depicted below made from grade 304 stainless steel.
the finished extruded shape weighs 9 pounds per foot. To machine
this part from a rectangular bar would require a bar 1.750"
X 5.000". This bar would weigh 27 pounds per foot. Thus to
machine this part one foot long would require the purchase of 27
pounds of material. In this instance, you not only pay more initially,
you pay for the cost of 18 pounds of surplus material, the cost
to machine this surplus material, and the cost of inbound freight.
Suppose the finished job required 4,000 feet of finished material.
The 9 pound extrusion would require one truckload of raw material.
The bar stock would require three truckloads of material. In this
instance, you pay for two truckloads of material that is machined
into chips and the surplus is scrapped. What are your machining
costs per pound of metal removal? Remember, you must machine away
18 pounds of stock.