If you work with milling machines, you have probably heard someone touting the benefits of variable end mills, especially when it comes to high speed machining. These tools may look like any other end mill, but some very small differences can have a very large impact on how they perform. If you have experienced annoying chatter or you are sick of lengthy material removal times, making the switch to variable cutting tools might make some big improvements to how your shop operates.
Chatter is one of the most irritating side effects of high speed machining. When tools spin rapidly, they naturally oscillate back and forth. Combining that regular horizontal movement with the regular operation of your end mills and you get countless hard impacts per second. Like the squealing of worn brake pads against a rotor, this hard metal on metal contact creates a shrill sound that is amplified when operating at high speeds.
The sound produced by tool chatter is not the only negative impact that high speed machining can have. Because tool chatter is the result of tiny impact forces, those impacts will also increase the fatigue on your tools’ cutting edges. These impacts, combined with the high temperatures caused by friction, can shorten the working lifespan of your cutting tools.
Variable end mills are a unique and almost counterintuitive solution to tool chatter. Cutting tools have to deal with high forces, which is why we arrange cutting edges symmetrically. This helps to evenly distribute the forces that the tool encounters. If your cutting edges are seriously misaligned, the tool will wear irregularly and the irregular forces could cause the tool to fail without warning. This is why it is so important to design tools that distribute force efficiently.
Despite this obvious truth of tool design, variable tools are designed to produce irregular cutting forces. The key is to create a tool where the irregularity in the force distribution is not severe enough to damage the internal structure, but just enough to disrupt the tool’s oscillation. To imagine exactly how this works, picture a child being pushed on a swing. When the same force is applied at the same point in the swing’s arc, the swing works in a regular manner and the arc gradually increases in size. If you change how hard you push and when you push in the swing’s arch, the path of the swing will become erratic and the child will have a harder time reaching the maximum height of the swing’s arc.
When a tool has irregularities to it’s cutting edges, its natural habit to oscillate is interrupted by irregular forces and the tool remains more stable. This decreases the intensity of micro impacts due to oscillation and the loud chatter that results. Different tool manufacturers achieve this effect by altering the helix angles or flute spacing of their tools, creating variable end mills that can run faster and quieter than their perfectly symmetrical counterparts.
If you are looking for some variable end mills for your shop, you can find them at Online Carbide. As an American manufacturer of high performance cutting tools, Online Carbide creates their own solid carbide variable helix end mills using extremely accurate 5 axis CNC guided grinding tools. Their tools are designed to operate at high speeds and feeds so you can increase your removal rates while you reduce chatter. The solid carbide construction of these tools also helps to provide a longer tool life. You can see their full inventory of end mills and drill bits when you visit www.onlinecarbide.com.