Yesterday I did a bit of what I have to consider as "SCARY" milling.
Using a HSS 3/32" end mill on a case-hardened, angled surface, for a two diameter long "notch" that ended up at the deep end as being about equal to diameter of the cutter. I had four such notches to make in a single piece of metal, and by the fourth cut I was getting definite evidence of grab and chatter that could well have broken that weak little bit. Clearly, that bit became progressively duller during its torturous ordeal. I was expecting for it to snap at any moment, leaving me with this critical task uncompleted.
I initially tried a plunge cut, but saw that poor little bit deflect down-slope on the angle, so knew that wasn't going to work. Coming in slowly and laterally at a fixed depth from open air allowed me to initiate the movement of metal, but the feed had to be so slow as to almost qualify as an abrasive rather than a cutter.
However, by nursing that poor brutalized little mill bit along at about 1400 rpm and feeding it at less than .010" depth per cut, I managed to complete all four notches without incident, though it seemingly took me forever to accomplish each of the four cuts. I doubt if I was feeding more than a very few thousandths a second, and still would feel the bit grab and catch in what must have been almost certain near breakage.
In reality I should have been using a 5/64" end mill but I didn't have one, and of course I also should have been using carbide, but didn't have that either, and as actual size of these notches was not super critical, going a little bit oversized was an acceptable option in this instance!
Think I was holding my breath the entire time, as this was the only end mill anywhere near that small that I had, so breakage would have left me short of completion, and would have meant needing to buy another end mill and wait for its arrival.
Whew!
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