If you’ve ever seen a picture of an end mill bit, you probably just assumed that they were drill bits. However, they are different. Drill bits are designed specifically to be able to go directly into the material. They cut axially and make cylindrical holes. On the other hand, end mill bits are normally used more for horizontal carving and cutting laterally. Some mills can cut axially as well as laterally.
Every end mill tip is shaped for a specific need. The most common shapes would be ball nose, v-carving, straight, fish tail and surface planing. Ball nose mills make a rounded pass which works for 3D work. Fish tails make a flat surface and v-carving mills produce a V shaped pass, obviously. This is mainly used for engraving or making signs.
If you already have a CNC machine, you need to make sure you have the right tools. You an’t just stick in a drill bit and hope for the best. The cutting surface of an end mill bit is called a flute. Typically, end mills will have as many as four flutes. A lower amount of flutes means that more chips are evacuated which keeps the bit cooler. On the other hand, having more flutes means that you can product a finer edge. Here are the four basic flutes.
- Straight Flute– typically used for general type cutting. It leave a good quality edge on most materials.
- Up Cut or Down Cut– these are spiral shaped end mills. They carry chips either up and away or down and into the material. An up cut keeps the bit cooler and is used typically on plastic or aluminum. A down cut bit will make sure that your top surface on a laminate material is smooth. These flutes help to avoid too much heat building up which could make the material stick to the end mill which would ruin it.
- Ball Nose Mill– As mentioned, these have rounded tips and are mostly used when making 3D pieces. If you combine this with a roughing bit, they work together to clear out bigger areas of the material. A ball nose end mill bit gives a smooth 3D finish, especially if you pass it multiple times.
- V Bit– V carving is done by using a 60 or 90 degree bit. It’s used to cut into very narrow areas. The wide bottom can be used on larger spaces. It can also make sharp corners when necessary. Other end mills can not usually do this because of their larger radius.
These are the four main bits but there are two more end mill bits that are often used. They are known as compression and table surfacing.
- Compression end mill bits combine the efforts of up cut and down cut mills so that the top and bottom are equally smooth. This is specifically for cutting laminated material and plywood. They can be used to cut at full depth passes which will cut down on time, considerably.
- Table surfacing are the bits that are used in order to surface a table ina short amount of time. It will leave the work surface smooth and level and ensure accurate cut depths.
CNC machining uses these rotational cutting tools or end mills in order to remove material. Basically, end mills are more versatile than drill bits. So, in conclusion- having more flutes is going to give you a smoother surface finish while having less flutes will make chip clearing a breeze and keep the bit cool. Having between two and four flutes are probably the most common. Other factors that play a big part in controlling the tooling effect are the direction of the cut, the size of the end mill, the speed at which you cut and the amount of chips that are being ejected. All of these things can damage the piece that you are working on.
If you are interesting in machining or becoming a machinist, understanding end mill bits is probably one of the most important things you can do in the beginning. If you don’t understand something as simple as that then you may want to consider specializing in another area of the industry if possible.
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