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I get lots of red sparks when cutting cast iron, am I going too fast?

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Grey cast iron, 7/16″ 4fl carbide endmill, .100 DOC, 40% axial engagement. GW called for 2900 rpm, 27ipm.

I got lots of red sparks all along the cuts, which generally indicates to me that it’s too fast. It also appears that my endmill flutes are getting eroded. I wonder if I’m better off using a larger HSS endmill and slower F&S as I don’t have coolant. Or greater DOC/slower?

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Either your cast iron is a different grade/condition than you may think (some of it can be quite hard) or there are some hardened inclusions the EM is hitting (also not that uncommon).

Dial back the surface speed a bit until it quits throwing so many sparks. An occassional spark would be fine, but a steady stream is too much. For starters, try bring up the material DB in GW Calculator and selecting the hardest grade of gray cast iron. See how that surface speed works for you. If it still sparks a lot, dial it back further by overriding the surface speed.

You shouldn’t need coolant for cast iron. If you have it, it’s purpose is largely just to keep the dust at bay. Cast iron has enough natural graphite that it doesn’t need the lubrication of coolant.

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