Chatter, dealing with the harmonic imbalance

Many sounds categorize the atmosphere of a machine shop, from the whir of a grinder, to the buzz of a tool cutting the part. One preventable sound specific to a machine shop that is chatter -- that annoying squeal or squeak from a machine. When you hear it, you know something is wrong.

Not only do you hear chatter but you can see it in the imperfect finish on the part. Everyone experiences it, but how do we fix it?

What is chatter?
Chatter is a harmonic imbalance that occurs between the tool and the workpiece because the part and the tool are bouncing against each other.

Remember it takes two to tango, so keep in mind that chatter can be caused by the tool bouncing against the part,the part bouncing against the tool, or both. It is not always easy to determine why chatter is happening, or which piece is the culprit.

How is chatter corrected?
There are several approaches to take when correcting chatter. With some careful setup and investigation, the problem can be isolated and fixed. Here is a list of items to keep in mind when correcting chatter.

May Cause Chatter	Should Fix Chatter
Before Machining
1.Tool setting	If the flat on the bar is not indicating parallel, an incorrect tool rake angle results in chatter. Make sure to indicate the flat on your boring bar.
2. Part setting	If the part is not correctly supported in the chuck, chatter may be a problem. Tap the part lightly with a wrench if the part rings like a bell it is not supported correctly
3. Final Part Shape	Perform boring operation prior to turning the outside diameter of a part to decrease the risk of chatter.

During Machining
4. Overextended Bar	Perform boring operation prior to turning the outside diameter of a part to decrease the risk of chatter.
5. Depth of cut	Try reducing the depth of cut to reduce chatter.
6. Feed Rate	Both high feed rates and low feed rates may cause chatter. The first inclination with chatter is to slow down the feed. Try increasing the IPR first. An increased feed bends the bar removing the tendency to chatter.
7. Chip Breaker style	The style of chip breaker may be causing excessive force, try changing to a positive style chip breaker.
8. Bar Support	If the bar is not correctly supported in the turret, use an extended bush or sleeve.
9. Surface speed	If the cutting surface speed is not harmonized between the tool and the part material chatter occurs. The first inclination with chatter is to slow down the speed. Try speeding it up first.

Advanced
10. Tool Pressure	To reduce tool pressure, change the nose radius of the cutting insert. A sharper insert nose radius has a lower cutting force. This is often a last resort solution because changing the nose radius of the tool requires changing the part program, cutter compensation, and feed rates.

Many of these solutions apply to lathe and boring bar use. Consider what these same changes will do when applied to milling or grinding chatter problems.

Chatter can be a complex situation. Remember the definition and tailor your solution to correcting the problem. When the tool and part are in "harmony" chatter is eliminated.