Solid Milling

How Do I Select The Right Material For My End Mill?

High-speed steel (HSS), powder metal (PM), and carbide are all materials commonly used in the construction of end mills. Each material offers different benefits depending on the application.

High-speed steel (HSS): HSS end mills are a cost-effective option for general-purpose milling. They offer good wear resistance and can withstand high cutting speeds. However, they are not as durable as other materials and are not recommended for cutting harder materials or for achieving a fine surface finish.

Powder metal (PM): PM end mills are made from a mixture of tungsten carbide particles and cobalt. They offer improved wear resistance over HSS end mills and can withstand higher cutting speeds. They are also more durable than HSS end mills and are suitable for cutting harder materials. PM end mills are typically more expensive than HSS end mills.

Carbide: Carbide end mills are made from a mixture of tungsten carbide particles and cobalt. They offer the highest wear resistance and durability of the three materials. They can withstand high cutting speeds and are suitable for cutting harder materials. They also offer good heat resistance, high-speed machining capability and the best surface finish quality. Carbide end mills are typically the most expensive of the three materials.

When choosing the right end mill material, it's important to consider the specific application, the materials being machined, and the desired surface finish. If a fine surface finish and harder materials are the main concern, carbide end mills are a better choice. If cost is a concern, HSS end mills might be a better option. PM end mills are a good balance between cost and performance.

How Do I Select The Right Flute Geometry?

Two-flute end mills: These have two cutting edges and are typically used for general-purpose milling. They are good for achieving a balance between chip removal and tool strength. They also offer good surface finish quality, and are good for slotting and plunge cutting.

Four-flute end mills: These have four cutting edges and are typically used for high-speed machining and for achieving a fine surface finish. They are good for finishing operations and for cutting softer materials. They offer good chip evacuation, which reduces the risk of tool breakage.

Six-flute end mills: These have six cutting edges and are typically used for high-performance milling. They offer the best balance between tool strength and chip removal. They are especially useful for cutting harder materials and for achieving a very fine surface finish.

Multi-flute end mills: These have more than six cutting edges and are typically used for high-performance milling. They offer the best balance between tool strength and chip removal, and are ideal for cutting harder materials and for achieving a very fine surface finish.

Helix angle: Helix angle is the angle between the flute and the tool axis, different helix angles can be beneficial in different machining scenarios, such as a low helix angle can be beneficial when cutting softer materials while high helix angles can be beneficial when cutting harder materials.

Chip breaker flutes: Chip breaker flutes are special flutes that are designed to break the chips into smaller pieces for better evacuation, this can be beneficial in situations where there is a high risk of tool breakage due to chip binding.

It's important to note that the best flute geometry for a specific application will depend on the material being machined, the desired surface finish, the cutting speed and the machine capabilities.

What is chatter when milling?

Chatter is a resonant vibration in the machine or workpiece. Chatter in machining is very bad for your tool life, interferes with the accuracy of the machining operation, and can shorten the life of your machine too. Chatter is not always a huge problem, sometimes you can still machine perfectly, maintaining the tools life and your machine.

Here's 8 ways to reduce chatter when milling.

1. Reduce The Number Of Flutes Sometimes, chatter can come from having too low rigidity and accuracy when machining, if you lower the number of flutes, you will increase your rigidity and therefore reduce vibration. 

2. Decrease The Chip-Load Per Tooth You can do this by reducing the feed or increasing the speed or RPM. Even though this will reduce chatter, slowing down the cutting process is not always the best course of action, and reducing the chip-load can be detrimental to the cutter. 

3. Check Your Work Holding Check that sufficient pressure is being applied to the workpiece by the chuck, vice, vacuum table or other work holding device. Try to apply clamping pressure to the part as evenly as possible using the right size work holder for the job. Avoid clamping just one end of a long thin piece of stock material (think about what happens when you twang a ruler on the edge of a table). If this is a likely problem consider using a larger work holding device or additional clamps on a mill. On a lathe consider using a tailstock or a steady rest. 

4. Find The Balance Vary your feed rates and spindle speeds by small amounts to find stable operating points. 

5. Rigidity Check Ensure that every part of your CNC machining set-up is as rigid as possible. If your Z axis, which holds the spindle, is just a little bit loose where it attaches to the gantry or bridge, that will translate to a much larger movement down at the end where your tool hits the material. If that's significant, the cut will waver, even if the tool is perfectly stiff. And if it's big enough, it will snap the tool, especially if it's small in diameter. Similarly, flex between the gantry and the rails it runs on will be magnified at the tool tip due to leverage effects. Your frame cannot be too rigid; any little bit of slop anywhere in the structure will be evident where the cutter meets the material. 

6. Go Big Or Go Home If possible, try using a slightly larger end mill with a larger core diameter. This will help improve the tools rigidity & stability. 

7. Longer Isn't Always Better Try to use a stub drill or a short length end mill as much as possible. The shorter it is in length, the higher rigidity it has. It also reduces the chances of the tool breaking. 

8. Uncoated = Sharper Use sharper inserts to reduce the cutting force of CNC milling machines. Clamp inserts are divided into coated and uncoated inserts. Uncoated inserts are usually sharper than coated inserts because if the inserts are to be coated, they must be passivated (ER-treated) at the edge. 

To summarise, chatter is bad. It can and most likely will damage your tooling & your machine. If you see any sign, or hear chatter or vibrations, attempt to reduce it immediately. There are many ways to reduce it, generally aim to ensure everything is tightened and locked in, and you make the tool & machining process as rigid and stable as possible.