[How do I?] Mill Hardened Steel

george wilson said:

Remove the set screws FIRST!

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Because they are basically made from tin and will melt? (in my experience)

I have a .045" thick cut off wheel for my angle grinder so I should be able to get all the way to the corner, I can easy enough slice .06 off. Then it would just be cleanup with the EM. I'll give it a try and report back.

The Chinese make them out C20-C40 steel, basically our 1020-1040 steel. They get just enough carbon-manganese mixture into the mixture to respond to heat treatment. They do some kind of carburized or nitrided heat treat to get the skin some what hard, probably around 50-55 HRC. The one's I've butchered up, I found the core to be relative soft in the 28-36 HRC range compared to the skin hardness.
Yeah, in my earlier statement, I meant to say power feed heavy so you don't loose your edge on the carbide endmill.

Well I got too impatient waiting for the carbide EM to show up so I tried a US hss EM. I ran the set screws out and used the cut-off wheel on the angle grinder to cut through the skin


I set the power feed a little higher than my gut said was the right speed and took the whole face (ended up being about .05") in one pass with constant brushing of cutting oil


Not a beauty, but it holds the parting tool block now

Glad it worked out.