Lathe Chatter Troubleshooting

Excessive Tool Wear

If your tool has excessive wear, the cutting forces generated by the cut will increase. These increased cutting forces can lead to chatter during the cut. 

Inspect your tool and replace it if necessary. 

It is normal for tools to wear over time. In a stable machining process the tool wear is predictable. This will allow you to use the Tool Life Management systems that come standard in your Haas control. The tool life information can be input in to the Haas control to alert the operator to replace the tool before it negatively affects your machining process.

Refer to the Tool Life Management section for details on how to use these systems.

Excessive Tool Stick Out

Longer tools are less stiff, and thus less stable, but even small changes to tool length can make a large difference: a 10% reduction in the length-to-width ratio results in up to a 25% increase in tool stiffness.

If you must use a longer stick tool for clearance, consider using a Haas Twin Turn or Extended Twin Turn BOT holder to fully support the stick tool. You can get these holders on parts.haascnc.com.

 

For boring bars, the material type of the bar will affect its stability. A steel boring bar (2) is stable up to a stick-out of 3 times the diameter. A carbide boring bar (1) is stable at a length up to 5 times its diameter. If you must exceed these limits, you must compromise your cut parameters to compensate for the reduced stability—reduce the depth-of-cut, feedrate, or spindle speed to compensate.


Note: Special vibration-dampening boring bars are available when you need an extreme length-to-diameter ratio to machine a bore.


Helpful Hint:
The set screws holding the bar in the holder can change the boring bar's resonant frequency. BOT holders have four set screws; two on each side. Best practice is to tighten the set screws on only one side of the holder. This ensures that the bar is held firmly against the BOT holder's bore. If you tighten the screws on both sides of the holder, then the bar may not be in contact with the bore, effectively floating in the center of the holder [1].



If you still have chatter issues using two screws on one side, you can loosen one of the set screws to change the bar's resonant frequency.

Chip Load too Light - Lathe

When the cutting speed (surface feet per min or meters per min) is too high or the feedrate (feed per revolution) is too low, the cut can become unstable and begin to resonate, leaving a chattered surface finish.

Reduce the cutting speed or increase the feed rate to stabilize the cut. Refer to the tooling manufacturer's instructions for guidance as to the best speeds and feeds to use for the tooling and workpiece material. Test-run your application and use spindle speed and feed overrides to find a speed/feed combination that does not chatter.

Tip: Check the tool insert box for cut parameter recommendations. Many manufacturers print the cut information directly on the insert box label.

The Tool is Not On the Spindle Centerline

If the cutting edge of your tool is not on the spindle centerline, excessive cutting forces can cause chatter, accuracy, and tool life issues.

Corrective Action:

Make sure that the stick tools are the correct size for your turret or tool holder.

Make sure that the seat under the insert is the correct thickness.

On Y-axis lathes, you can use a Y-axis tool offset to bring the cutting edge to the spindle centerline.

Inspect and correct any alignment errors in your machine tool.

The Tool Insert is Improper for the Workpiece Material

Insert selection is critical for a stable cut. The chip-breakers, coatings, radius sizes, geometry, and carbide grade must be designed for the workpiece material. Improper inserts can cause problems with surface finish, tool life, and chatter

Corrective Action:

Consult with your cutting tool vendor to select the proper insert geometry, radius size, coating and carbide grade for you application.

The Workpiece Moves in the Chuck

If your workpiece moves in the workholding during  the cut, you will have accuracy issues, difficulty holding tolerances and chatter issues. 


Incorrectly bored chuck jaws can let the workpiece move. The soft jaws should be machined to match the nominal size of the part being held. 


Be sure to use a chuck jaw support slug (1) or adjustable boring ring (2) in the center travel of the jaws, before you machine the jaws. If the Jaws are too close to the top of the stroke you will have diffucalty loading and unloading your workpiece in the jaws, if the jaws are too close to the bottom of the stroke the full clamping force will not achieved.   



Use a 0.001" (0.03 mm) feeler gauge to check for gaps between the workpiece and the chuck jaws. Check both the front and the back. The jaws may have deflected from the clamp force, in some cases you may need to machine a slight taper in the jaws to compensate for the jaw's deflection allowing for full jaw contact with the workpeice . 

Make sure that the chuck jaws are tight, and that the screws do not bottom out on the T-nuts or T-slot. The T-nuts should not extend outside the T-slots. 


When OD clamping parts, the centrifugal forces generated at high RPMs will reduce the clamp force and may allow the part to move. Use this chart to determine the if you need to increase the clamp force on the chuck or reduce the max RPM during your program. You can find this chart on a sticker near the hydraulically pump on your lathe. 

Refer to the How to Properly Cut Lathe Soft Jaws — Part 1: Fundamentals and OD Gripping and How to Properly Cut Lathe Soft Jaws — Part 2: ID Gripping, Re-cutting, and Adding a Taper videos for more details on cutting soft jaws.

Note: Be sure to clean and deburr you workpiece before you clamp it into your workholding device. A dirty surface, chips, or burrs can let the workpiece move during the cut.
  
 

Insufficient Support on the Workpiece

If the workpiece is not properly supported, it will begin to vibrate and introduce chatter into the cut. 

As a general rule, if the portion of the workpiece that extends past the chuck exceeds a diameter-to-length ratio of 3:1, use a tailstock to stabilize the cut. 

If the length-to-diameter ratio of your workpiece exceeds 10:1, you may need to use the additional support of a steady rest, different workholding, or a different machining strategy to stabilize the cut.

Helpful Hint:
Consider using the Spindle Speed Variation (SSV) feature to disrupt chatter.

For more details on tailstocks watch Tailstock Fundamentals: How to use the Tailstock on a Haas Lathe.

Worn or Damaged Live Center

A worn or damaged live center can introduce vibrations and let the part move. This can cause chatter, taper, poor surface finish, and tool life issues.

Inspect live centers for excessive runout and damaged bearings while they’re still in the machine.

Check runout by placing an indicator on the 60 degree point, then gently rotate the center's point. The TIR should be within the manufacturer’s specification.


Check for bearing wear by gripping the point firmly and rotating it in one direction. The spindle should turn freely, if you can feel hesitations or roughness this indicates bearing wear.

Note: Live centers have a service life and a maintenance schedule. Refer to the live center manufacturer's documentation for details on your live center.
Tip: Excessive tailstock pressure can prematurely wear out your live center.

The Center-Drilled Hole is Incorrect or Damaged

If the center-drilled hole has the wrong angle, is too small, too shallow, too deep, or is damaged, the live center will not have sufficient contact with the workpiece to properly stabilize the cut. 


Be sure to use a 60° center drill tool. Countersink tools do not have the tip relief required for the live center.  


Inspect the center-drilled hole. If necessary, machine it again.

For more details center-drill requirements watch this video on Tailstock Fundamentals.

 

Coolant Issues

Incorrectly aimed coolant nozzles or obstructions in the stream can prevent coolant from reaching the cutting area. Adjust your coolant nozzles to deliver coolant to the cutting area.

Be sure to use the recommended coolant mixture concentration in your applications. If your concentration is too lean, the reduced lubricity can negatively affect your tool life and surface finish.
There are many different coolants for different applications and materials. Contact your coolant dealer for advice.

Refer to the Machine Tool Coolant Series page for videos and articles about maintaining your coolant system.

Inadequate Foundation

The machine must sit on a solid and stable foundation. Refer to Pre-Installation Information for a full description of the foundation requirements.

If the foundation is badly cracked, move the machine to a location with a solid foundation, or repair the foundation.

The machine should sit on one continuous slab of reinforced concrete. If the machine straddles more than one slab, you may need to move the machine to a single, continuous slab.

Example of a Machine Set Across Multiple Concrete Slabs

 

 

Be aware: Many service and repair procedures should be done only by authorized personnel. The service technicians at your Haas Factory Outlet (HFO) have the training, experience, and are certified to do these tasks safely and correctly. You should not do machine repair or service procedures unless you are qualified and knowledgeable about the processes.

Danger: Some service procedures can be dangerous or life-threatening. DO NOT attempt a procedure that you do not completely understand. Contact your Haas Factory Outlet (HFO) and schedule a service technician visit if you have any doubts about doing a procedure.