03-04-2015, 04:09 PM
Cut it dry and see how tool life improves. The only thing a dab of oil does for carbide is make smoke and smell. Thermal shock to the inserts is caused by the intermittent application of cutting fluids, which is exactly what you get in a milling operation because the insert is "in and out" of the cut constantly. What leads you to believe a little oil helps? Quite the opposite!
What diameter is the cutter? It looks to be either 20 or 25mm judging by how much bigger it is than the 16mm width of the workpiece. I never run a cutter with missing inserts because you can easily damage the unoccupied insert pockets. Why do you do that? The heat of cutting is definitely enough to cause thermal shock micro cracks which are often disguised as tool flank wear because the edge erodes away the crack propagation. Heat is carried away by the chips (ideally), but it does get hot enough in the cutting zone just off the edge of the insert but is definitely hot enough to cause the edge cracking at 1200 rpm. Use all four and take a lighter depth of cut if HP is the limiting factor.
What diameter is the cutter? It looks to be either 20 or 25mm judging by how much bigger it is than the 16mm width of the workpiece. I never run a cutter with missing inserts because you can easily damage the unoccupied insert pockets. Why do you do that? The heat of cutting is definitely enough to cause thermal shock micro cracks which are often disguised as tool flank wear because the edge erodes away the crack propagation. Heat is carried away by the chips (ideally), but it does get hot enough in the cutting zone just off the edge of the insert but is definitely hot enough to cause the edge cracking at 1200 rpm. Use all four and take a lighter depth of cut if HP is the limiting factor.