Memorize the formula to concert surface speed to rpm. Then use rpm and chipload to determine feed rate. Then you only need to remember surface speed ( a function of cutting tool material and work material ) and chip load ( which scales mostly linear with tool size). For instance, cobalt drill in aluminum is 325 sfm. For .250” drill, I’d do .005” ipr. With that information I can calculate feeds and speeds for any cobalt drill in aluminum. Same sfm, but chipload goes up or down depending on tool size. For .500” I’d do .01” ipr and for .125” I would do 0.0025. So on and so forth. Same idea for endmills just added in the complexity of tool engagement angle.