The biggest cause of failure with carbid cutters is when the cutter is entering and exiting a cut. When hand feeding, its really important to be winding as evenly as possible to the finished length. If the end is open, then slow down for the end run out and be slow at the start of the cut. When hand feeding, and if you are erratic or have an actual stop, then in reality it should be a slow restart. I rarely run my mill faster than 1200 rpms and find the cutters lasting a long time of cutting. Keeping the swarf away is another big life enhancer, so where possible, I have the vacuum cleaner running to dray away the swarf. Sometimes I need a gentle air blow when down in slots, as the vacuum wont draw out the swarf. As I am a home hobby milling , I have not yet filled the mill or lathe coolant tank. I prefer to use a light coating of cutting oil and be conservative on the feedrate. When cutting some bearing lately, the 3mm cutter came from a NZ supplier and labelled as hard cutting. I bought 2 as I was certain it was going to wear or create burrs after just a few bearing shells, but it lasted for the whole project. Cutting the bearings was 200rpm and just a slow stead infeed for the small distance of around 0.35mm or so.
Where ever possible I avoid black scale bar. If I have to mill it, I get onto the linisher and take most of it off on two sides. Then with usually a tip end mill, cut under the skin from the clean end face. The outer skin on black bar just destroys tooling.
With my new DRO it has rpm readout of the spindle. Its really handy to know , as you can work out roughly how fast to wind the handle per second or per minute to get the feed rate for the cutter being used. Some dro's now have the mm/min feedrate on the axis you are winding which will help with cutter life dramatically.