I bought several at a tool reseller and have used them but some of the conversations here have made me wonder.
The ones I have are spiral cutters and clearly sharp on the end. They plunge better than a drill bit and will cut sideways. Most of them have two flutes but one has three.
So, what makes them different from a router bit or a drill bit?
And, I see videos of CNC machines cutting bunches of parts out of plywood or MDF and they appear to get a lot more mileage out of a bit than I do. What are they using.
I use end mills instead of router bits whenever possible. 2, 3, or 4 flute mills all work well. 2 flute ones seem to cut wood faster than the others. I have 1/4, 3/8, and 1/2" collets for my routers and they can handle pretty much all the mills I commonly use.
"they appear to get a lot more mileage out of a bit than I do. What are they using."
They have plenty of hp and control of the speed to take the proper size chip. Whether talking saw blades or router bits or planer knives, feeding too slow generates heat. When the chip is larger, the chip takes the heat out with it, so feeding too slowly will dull bits faster. Now,,,,,,,, I'm not suggesting that anyone should just cram things through just tearing out larger chunks is better either. With routers, I find it easier to find the right feed rate with a larger more powerful router than with those with less power.
The mills are all carbide and this grade lasts longer than welded on insert
They are coated with the coating designed to promote long life in whatever they are cutting, for example vanadium nitride for corrosion wear resistance.
The CNC program drives the cutter in a consistent motion at an optimum speed and depth to minimize damage to the bit. Something we all try to do, but the computers are much better at it.
But I have no quantitative data or analysis to back it up.
I've just seen the vastly better cuts achieved by power feeding stock past the cutter and can imagine that it gets even better with optimization to prevent excessive chip loading in the flutes (=heat).
End mills are designed to be run in mills which are designed to cut metal not wood.
They come in different shapes with different numbers of flutes.
Most if not all are made of solid carbide (as was already pointed out).
Mills cut with a stationary cutter head and a moving table (except CNCs).
Feed rate is really important in cutting metal. Get too fast and breakage can occur.
End mills cutting metal are lubricated with cutting oil.
When an end mill breaks it makes a horrible noise. I should know I broke one at gunsmith school. The gibs in the table were loose. I started a very small movement and the gibs moved a lot. Turned my end mill into a "ball end mill" and drew every instructor in ear shot to me.
