Tools for machining aluminium are sometimes given a coating of TiAlN. However, the coating cannot be used at temperatures above 600 degrees C, or on ferrous metals. A PCD coated tool may last up to 100 times longer than an uncoated tool. Polycrystalline diamond (PCD) is an exceptionally hard coating used on cutters that must withstand high abrasive wear. Coatings: The right tool coatings can have a great influence on the cutting process by increasing cutting speed and tool life, and improving the surface finish.However, the large number of flutes leaves little room for efficient swarf removal, so they are less appropriate for removing large amounts of material. A finishing cutter may have a large number (4 or more) teeth for removing material carefully. These teeth leave a rough surface behind. A roughing cutter may have serrated teeth for breaking the chips of material into smaller pieces. Roughing or Finishing: Different types of cutter are available for cutting away large amounts of material, leaving a poor surface finish (roughing), or removing a smaller amount of material, but leaving a good surface finish (finishing).However, these cutters can cut downwards at an angle of 45 degrees or so. This is because the teeth of some cutters do not go all the way to the centre of the end face. Center cutting: Some milling cutters can drill straight down (plunge) through the material, while others cannot.Typically, finishing cutters have a higher rake angle (tighter helix) to give a better finish. Setting the flutes at an angle allows the tooth to enter the material gradually, reducing vibration. If the flutes were straight, the whole tooth would impact the material at once, causing vibration and reducing accuracy and surface quality. Helix angle: The flutes of a milling cutter are almost always helical.So, a 4-tooth cutter can remove material at twice the rate of a 2-tooth cutter. Typically, the more teeth a cutter has, the more rapidly it can remove material.
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Milling cutters may have from one to many teeth, with 2, 3 and 4 being most common.
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Often, the words flute and tooth are used interchangeably. There is almost always one tooth per flute, but some cutters have two teeth per flute. The tooth cuts the material, and chips of this material are pulled up the flute by the rotation of the cutter. Flutes / teeth: The flutes of the milling bit are the deep helical grooves running up the cutter, while the sharp blade along the edge of the flute is known as the tooth.Shape: Several standard shapes of milling cutter are used in industry today, which are explained in more detail below.There is also a choice of coatings, as well as rake angle and number of cutting surfaces. Milling cutters come in several shapes and many sizes.