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Took a 0.06 inch deep cut on a 4140 shaft and scrapped a $700 part
Was running a batch of 4140 shafts on the Haas lathe at the shop in Dayton last Tuesday and pushed the roughing pass too hard. Insert chipped on the third part, tool walked about 0.03 into the wall, and that shaft was done. I stopped the run right there, dialed the depth back to 0.04 and changed the insert every four parts instead of every eight. Still hit the ship date, but I want to know what depth of cut you all run in 4140 without babying the tool.
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taylor_barnes5911d ago
The "changed the insert every four parts instead of every eight" line got me because I have absolutely been the guy who tried to stretch an insert one more part and paid for it with a scrapped blank, so welcome to the club, we meet on Tuesdays. On your actual question, for 4140 in the low 30s on the C scale I run roughing around 0.08 to 0.1 per side with a decent coated carbide and it holds up fine as long as the tool is on center and I'm not starving it. The catch is that 0.04 might actually be worse for tool life than 0.06 in some cases because too light a cut rubs instead of cutting, which work hardens the surface and eats the insert from the flank. What insert grade and nose radius are you running, because that matters more than the depth number by itself. Also check your coolant aim, 4140 will tell on you fast if the chip is dragging heat back into the edge.
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