User talk:Rocketmagnet/MillingScratch

When used for plunge cutting (vertically down as when drilling), one of their frontal cutting edges should be across the center for the correct cutting action to occur as shown in the image opposite, with the end view of the slot drill. Slot drills are mostly used only when it would be too time consuming to pre-drill a hole for an endmill and there isn't enough room for the end mill to plunge using a helical motion. That is because slot drills don't drill very well; the cutting edge that crosses the center of the mill (center-cut) actually spins the wrong way on the part of it that crosses the center.

Two flute end mills can be used for plunge cutting. They are also called center cutting because they can start their own hole.

Three flute end mills are a good choice for slotting and provide an acceptable surface finish. Two teeth are in the cut most of the time, reducing chatter.

Four flute end mills only cut on their periphery and can plunge cut when a starting hole is pre-drilled or if instead of simply drilling down into the workpiece, perform a three-axis helical motion. They are generally stronger than a two or three flute end mill, therefore allowing for increased feed rates.

Early endmills and most large endmills have a recessed center at each end of the cutter to facilitate resharpening, this results in the full cutting edge being unavailable. The image at right shows two end views (center row) of an endmill that illustrate this. Some endmills also have rounded corners, either concave radii (fillet endmills), or convex radii (bullnose).