flat end leaves flat surface profile on the stock and are good for removing large volume of material, but steps are formed when used for making curved surfaces. Ball end leaves curved surfaces and forms smooth curved finish while cutting cavities. They are used for finishing cuts.
Upcut & Downcut
In an Upcut type end mill the teeth on the flute will point upwards. This means that the end mill is cutting and drawing out the wood through the flute. This is good for cutting deep into the stock. But this leaves a bad surface finish on the top of the surface.
A downcut type end mill has teeths that point downward on the flute. This means that the end mill will cut and try to push the material into the stock. This will give good surface finish on the top, but it is not very efficient at removing material.
Drill bit Vs Endmills: A drill bit needs to cut straight into the material hence will have teeth at tip. But an Endmill needs to cut from the sides also, that means it needs to have a cutting edge spiralling all the way up to the flute.
Bit material: Router bits used in Shopbot are made from a variety of materials such as solid carbide, carbide-tipped steel, and high-speed steel.
Flute type: There are four basic flute types: Straight, spiral up-cut, spiral down-cut, and compression