03-27-2019, 06:50 AM
Hey Pete,
First of all, your rpm is way too low. A carbide end mill running in 4140 should be up around 4000 rpm. I generally use a depth of cut of about 1/8 the diameter of the end mill, or about .05" for your application. A shallow cut at a higher feedrate is much easier on end mills than a deep cut at a slower feedrate. You can go deeper if the end mill is exposed, but in a slot like that, shallow depths allow the chips to clear better.
The formula I use for rpm using HSS is 4 x cutting speed in surface feet per minute divided by the diameter of the tool (or work for turning). Carbide can be run at least 4 times as fast.
Tom
First of all, your rpm is way too low. A carbide end mill running in 4140 should be up around 4000 rpm. I generally use a depth of cut of about 1/8 the diameter of the end mill, or about .05" for your application. A shallow cut at a higher feedrate is much easier on end mills than a deep cut at a slower feedrate. You can go deeper if the end mill is exposed, but in a slot like that, shallow depths allow the chips to clear better.
The formula I use for rpm using HSS is 4 x cutting speed in surface feet per minute divided by the diameter of the tool (or work for turning). Carbide can be run at least 4 times as fast.
Tom
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