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Thought high feed rates were for showoffs until my insert blew up on a 4140 shaft last Tuesday
I was running a 4140 shaft on the lathe last Tuesday and kept the feed at my usual 0.008 per rev because I figured going faster would just eat inserts. Around the third pass the chip started turning blue and the insert cracked clean in half, so I bumped it up to 0.012 and the chips finally started breaking instead of birdnesting. Turns out I had it backwards the whole time, so what feed and speed are you guys running on 4140?
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the_seth10h ago
Man, blue chips and a cracked insert on 4140? Been there and it stings every time. I ran 0.006 feed forever because some old timer told me slow feeds make inserts last, and all I got was birds nests wrapping around the turret and heat building up right at the tip. Bumped to 0.011 and suddenly chips were breaking into little sixes and nines and the insert stopped cooking. With 4140 you gotta let the tool bite or it just rubs and work hardens on you. I run around 550 SFM and 0.011 feed on roughing with a decent coated insert and it holds up way better than babying it.
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