Turning inserts are economical, replaceable, and sometimes even indexable metal cutting tools that enable efficient machining operations with a lathe. They can also be replaced when worn, damaged, or otherwise as needed to improve the efficiency of the lathe with which they’re used.
That being said, one phenomenon well-known to machinists, called chatter, can wear out or break your turning inserts long before their time. Here’s what it is, in the event you’re unfamiliar, why it’s a problem, and what you can do about it.
What Is Chatter, What Causes It, and Why Is It a Problem?
In machining, chatter is the result of either a workpiece or the metal cutting tool used, in this case a turning insert, experiencing deflection (flexing or bending) and then returning. Some imbalance between them causes deflection which results in the vibration that causes chatter.
Chatter manifests on the surface of a workpiece either as irregularities in the finish, or else it results in a finish that is not of the desired quality, given the workpiece material and metal cutting tool used. On top of that, chatter can inflict severe stresses on cutting tools that can result in breakage as well as in premature wear. Chatter also commonly results in a loud, instantly recognizable noise, giving rise to the name.
Worse yet, there are many causes of machine chatter when using a lathe and a cutting tool with a turning insert. Figuring out what exactly is causing the chatter can be problematic, but there are some common causes; being able to identify them can help you solve the issue at the root.
Solving the Issue of Chatter
One common cause of machine chatter in lathe operation is spindle speed. If the speed is too high or too low, the cutting tool may resonate, resulting in chatter. Feed rate, which is how quickly you run the turning insert over the workpiece, can also cause chatter. Slowing down feed rate can often reduce or eliminate chatter. However, both high and low feed rates can cause chatter.
Cutting depth can also influence chatter. Generally, if the cutting depth is too deep, chatter can occur, although it is also possible that a shallow cutting depth can induce chatter as well.
Tool overhang is another cause of machine chatter. If the tool is too far overhung, there is a higher chance of the cutting insert resonating and thereby causing chatter. Turning insert nose radius is another causative agent here; generally, but not universally, a smaller nose radius is less prone to chatter.
However, how you run the machine is not the only thing that can cause chatter in lathe operations. Working with a turning insert that is too worn or too dull can also cause chatter, as can improper or uneven support of the workpiece. If the operation requires a start hole, and it is improperly bored, that can cause chatter as well.
Also, if the operation warrants the use of coolant and coolant is applied improperly or inefficiently, that can also cause or exacerbate machine chatter.
Ultimately, at the end of the day, being aware of these causes of chatter (though they are not the only ones) can help prevent premature wear to your turning inserts, uphold a higher standard of quality for the finished workpiece, and also help reduce the incidence of tool breakage.
Need New Turning Inserts? Bookmark TMT Toolbox
In the event you landed here because you need new turning inserts, or at least a reputable supplier where you can source them, along with end mills, drills and other metal cutting tools and machine tool accessories, bookmark TMT Toolbox. They carry a wide range of high-quality machine tool accessories and can help you out when you need to replace anything.
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