When milling a material like aluminium, it may be advantageous to use a tool with very deep, polished flutes (2,3 flute) with a high helix rate and a very sharp cutting edge. When machining a tough material such as stainless steel, however, shallow flutes (4,6,8 flutes) and a squared-off cutting edge will optimize material removal and tool life.
4 flute endmills can be used to cut soft metals but chips will clog up the flutes at high feed rates resulting in a poor surface finish.
2 flute endmills can be used for steel but will wear quickly resulting in very short tool life.
I have found that when I keep a seperate set of endmill and lathe cutting tools for non-ferrous metal use they stay sharp much longer with excellent surface finishes even with solid carbide tooling. I grind seperate lathe tools for ferrous and non-ferrous metal use with different front and side relief angles... 10 degrees is better for aluminum and 5 degrees is better for steel, carbide is better for hard steel and cast iron. Different grades of carbide are available for the various grades of cast iron, steel and aluminum too.
Professional cutting tools with a specific geometry, coating, material and feed rate are available that can outlast standard cutting tools 10 to 1.
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This message has been edited by Boomer_Mikey on Jul 28, 2012 9:58 AM