Face milling cutter spindle speed and feed rate

Face Milling Basics

What is Face Milling? Imagine milling with the side of an end mill. The general term for this is “peripheral milling.” Now, what if we cut from the bottom?

Technically, that’s face milling, though we usually use the term only when using a special type of end mill called a “face cutter” or “sleeve cutter.” Note that there is actually no difference between face cutters and sleeve cutters.

You might also hear “face milling” referred to as “surface milling.”

Let’s first choose the face cutter best suited to your face-milling needs. The most significant differences between face cutters are:

Tool Diameter: Face cutters are available in both large and small diameters. Determine the tool diameter so that the cutting speed (feed rate), spindle speed, and cutting horsepower requirements are within your machine’s capabilities. You will get the best finish if the cutter’s maximum cutting diameter is larger than the area you are facing. However, larger cutters require a more powerful spindle and are not always suitable for narrower areas.

Number of Inserts: The more inserts, the more cutting edges, and the faster the feed rate of the face cutter. Higher cutting speeds mean the job can be done faster. A face cutter with only one insert is called a fly cutter. But faster isn’t always better. Unless you can adjust the height of each insert, your multi-cutting-edge face cutter won’t achieve the same smooth finish as a single-insert fly cutter. Generally, the larger the cutter diameter, the more inserts you’ll need.

Geometry: This depends on the shape of the inserts and how they are secured within the face cutter.

Let’s take a closer look at this geometry.

Choosing the Best Face Cutter: 45 Degrees or 90 Degrees?

First, what are we talking about when we say 45 degrees or 90 degrees? Looking at the comparison of the two cutters above, the answer is quite apparent. It’s about looking at the angle of the cutting edge on the insert.

This angle is the angle of the cutting edge; the cutter on the left is 45 degrees, and the cutter on the right is 90 degrees. This angle is also called the cutter’s lead angle.

Here are the optimal operating ranges for different face cutter geometries:

By the way, round insert face cutters are also called “button cutters.”

So which one offers better results for face milling?

Of course, having both 45-degree and 90-degree face cutters would be ideal. What are the advantages and disadvantages of each?

Advantages and Disadvantages of 45-Degree Face Cutters

Advantages: Sandvik and Kennametal both state that 45-degree cutters are a better choice for general face milling. Their reasons for choosing 45 are:

Better-balanced cutting forces, resulting in more uniform axial and radial forces. Reduced radial forces, making them more balanced with axial forces, not only improve surface finish but are also more beneficial for spindle bearings.

Better entry and exit performance—less impact and less tendency to break out.

The 45-degree cutting edge is better suited for demanding cuts.

Better surface finish—the 45-degree cutter produces significantly better finishes. Lower vibration, balanced forces, and a better entry geometry are three reasons for this.

The chip-thinning effect comes into play, increasing the feed rate. Higher cutting speeds mean higher material removal rates and faster job completion.

45-degree face cutters also have some disadvantages:

The maximum depth of cut is reduced due to the lead angle.

A larger diameter can lead to clearance issues.

90-degree angle milling or square shoulder milling is not possible.

It can cause chipping or burrs on the rotating tool’s exit side.

The lateral (axial) force applied at 90 degrees is smaller, about half that of face cutters. This is advantageous in thin-walled structures, as transferring too much force to the wall can cause material chatter and other problems. This can also be an advantage when it is difficult or even impossible to hold the part in a fixture securely.

To avoid forgetting face cutters, they combine some of the advantages of each face cutter, and they are also the strongest. Therefore, if you are dealing with difficult-to-machine materials, milling may be your best option.

If you are primarily aiming for perfect results, then you may need a fly cutter. In most cases, fly cutters provide the best surface finish. Incidentally, you can easily convert any face cutter into a fine fly cutter with just one cutting edge.