The figure illustrates the structure of an end mill, a milling cutter widely employed in CNC milling. Its design comprises cutting edges positioned on both the cylindrical surface and end face. The primary cutting edge, located on the cylindrical surface, is typically a helical tooth. This feature enhances cutting stability and elevates machining accuracy. However, it is important to note that the end mill lacks a cutting edge at the center of its end face. As a result, the end mill cannot be axially fed. Instead, the end face edge is primarily employed to process the perpendicular bottom plane alongside the sides.
To tackle the problem of chip curling and clogging, it is recommended to use an end mill with a relatively small number of cutter teeth and a larger radius of the chip groove arc, which allows for more space and prevents the chips from getting stuck. For instance, for coarse-tooth end mills, the number of teeth is usually between 3 to 4, while the number ranges from 5 to 8 for fine-tooth end mills and 10 to 20 for those with sleeve structure. The arc radius of the chip flute should be around 2 to 5mm. For larger diameter end mills, it may be beneficial to adopt an unequal pitch structure to strengthen the anti-vibration capacity and ensure stable cutting process.
When it comes to the helix angle β of end mills, there are different variations depending on the type of teeth they have. In the case of standard end mills, the helix angle ranges from 40° to 45° for coarse teeth, while for fine teeth it ranges from 30° to 35°. On the other hand, sleeve type end mills have a smaller helix angle, usually falling between 15° to 25°. This variation in helix angle is essential as it affects the performance and cutting ability of the end mills.
To accommodate smaller diameters, end mills are typically created as shanks. Straight shank end mills are used for sizes ranging from φ2 to φ71mm, while those with φ6 to φ63mm are designed with a Morse push shank. For sizes between φ25 and φ80mm, a 7:24 taper shank with screw holes is utilized, which allows for easy tool tightening. Sleeved end mills are an option for larger diameters, ranging from φ40 to φ160mm. Regardless of the size, carefully selecting the right end mill ensures optimal cutting performance.