For those of you familiar with CNC-machining, you’ll likely remember it wasn’t long before you came across the term “chatter” in this line of work.
Chatter is a condition that commonly afflicts cutting tools, machines, and workpieces - and it is undesirable, but there are things you can do to prevent it.
What Is Machine Chatter?
In the process of CNC-machining, not only the machine and the cutting tool but the workpiece itself are subject to vibration and dynamic interaction.
The components are literally vibrating and bouncing against each other, and these effects can be magnified through harmonic imbalance.
If the harmonics and increased vibrations reach the resonant frequency of the cutting tool, machine, or workpiece, it will magnify the vibrations.
When this happens, it produces a characteristically loud noise - that is, “chatter,” which is commonly used to explain the condition.
What Causes It?
Chatter can be triggered by a wide range of factors. One is operating the machine at speeds that naturally approach the resonant frequency of the cutting tool.
Chatter can also be caused by improper tool holding, suboptimal machine conditions, or running the machine at speeds that are too high or too low.
Cutting tool selection can also increase the frequency of chatter - for instance, if a tool with too many cutting flutes is used, or one that does not facilitate material removal rates, it can cause or exacerbate chatter.
Why Is Machine Chatter a Problem?
Machine chatter is an undesirable consequence of any or a combination of the factors mentioned above, and it can adversely affect a variety of processes.
Often, chatter leaves telltale wavelike patterns or undulations on the surface of a workpiece, marring the finish.
Chatter can also accelerate the wear of a cutting tool and decrease tool life, particularly in rigid, solid carbide mills. It can even break them if the stresses are high enough.
Moreover, chatter puts stresses on the tool holder and machine, which can result in higher maintenance costs, downtime, and delayed deliveries.
How Can You Help Prevent It?
Fortunately, there are multiple things you can do to prevent or alleviate chatter:
● Use a more rigid/stable cutting tool:
Shorter end mills, like stub length end mills, and end mills with larger core diameters, tend to be stockier and more rigid, which helps to combat vibrations that cause chatter.
● Use variable flute end mills:
Variable flute end mills have “uneven” or variable flutes that discourage the tool from reaching a resonant frequency.
● Reduce feed rate or increase RPM to enhance chip evacuation:
Altering machine speed is the most common approach to preventing chatter, and although it is not always effective, it can fight the symptoms.
● Using high-quality work holders:
Strong, rigid clamps and work holders can help combat the micro-movements and reduce vibrations that cause machine chatter.
● Larger diameter, shorter-overhang tool holders:
Stronger, more rigid tool holders can help prevent the vibrations that cause chatter.
● Keeping your machine on a regular maintenance schedule:
Worn or failing parts can cause almost imperceptible variations in machine performance that become perceptible when they cause chatter. Sticking to routine maintenance can help prevent these concerns.