CNC End Mill Comparison Guide

Shape

From one end mill to the next, the most obvious difference you will find is that end mills come in many shapes and sizes. Some are thin and pointy, and others are wide and rounded. Some of the most common shapes you will find are fishtail (or flat), ball-nosed, and the bullnose, and each of these can be a straight cut or a tapered cut.

Size

Size is the biggest determination of what you can do with any given end mill. Large ones excel at grinding through a lot of material at once, but you don’t get a lot of detail out of your parts. With CNC milling, the radius of your end mill is the radius of any internal corner, so you will almost never have a perfectly square corner on the inside of a milled object. Smaller and smaller end mills can be used for each pass to clean up an edge and get the part to the final dimension and shape. ;

Straight vs. Tapered

There are generally two forms of end mills: straight and tapered. This is a choice based on the geometry of your finished part because a tapered end mill won’t be able to do all the same things as a straight end mill, and a straight end mill may not be the most efficient choice. By using a tapered end mill, the cross-sectional area is larger than a straight end mill of the same tip diameter, creating a much stronger end mill that is less likely to bend while milling. For perfectly vertical walls you will need to use a straight end mill as the taper just won’t reach. However for angled walls, using a straight end mill is not the most efficient, ideal choice.

Why Use a Single Flute End Mill?

There are a lot of strange beasts out there in the cutting tool world and a lot of physics that are not obvious. For example, many machinists will know that more flutes mean more productivity, but that certain materials, like aluminum, require fewer flutes–usually two or three. If that's the case, when would it ever make sense to use 1 flute end mill? Is there a time when the least number of flutes possible is a good idea?

Now let's take a CNC Router example. ; Say it's got a spindle capable of 24,000 rpm, but it will go no slower than 12,000 rpm. ; When cutting aluminum, the first thing we discover is we need carbide to run at those surface speeds–preferably a good coating is needed to up the limit even more. As we begin working through the feeds and speeds (hopefully using G-Wizard Calculator!), we discover we're going to need some pretty high feed rates at those RPMs too. ; For a 1/4″ endmill, it wants to run at 24000 rpm and a feed rate of about 255 IPM. ; ;Now depending on the machine, we may have discovered a problem. What do we do if our machine can't feed that fast?