CNC Lathe Chucks: Troubleshooting common problems

Possible causes and solutions for common chuck problems such as:

1. Component slippage 
2. Excessive Vibration
3. Master Jaw not moving
4. Poor Accuracy
5. Base Jaw Breakage

Troubleshooting: Component slippage

1. Lack of lubrication on master jaws & moving parts -Lubricate master jaws through the grease nipple
2. Component Clamping at end of the stroke -Clamp the component at the middle of the Jaw stroke to avoid slippage.
3. Speed is excessively high -Reduce the speed level to obtain necessary chucking
4. Cutting forces too high -Calculate cutting force & check against chuck specifications
5. Insufficient chucking force -Check hydraulic pressure setting

Troubleshooting: Excessive Vibration

1. Run out on chuck body beyond permissible value-True the chuck body within permissible value as specified
2. Top jaws holding the job not symmetric with the rotation axis and therefore causes imbalance -Chuck with the special jaws and component to be dynamically balanced
3. Draw tube / Draw bar may be out of centre or out of alignment -Check and correct the alignment

Troubleshooting: Master Jaw not moving

1. Chuck with dirt from burrs & chips - Dismantle & do periodic maintenance.
2. Internal parts of Chuck broken/ jammed -Replace broken parts & do periodic maintenance.
3. Check cylinder for malfunction.

Troubleshooting: Poor Accuracy

1. Excessive height of top jaws -Reduce the height of top jaws as recommended by GMT
2. Guide ways of the internal parts of the chuck could be worn out -Recondition the chuck /Replace the chuck with new.
3. Too much chucking force - Reduce the chucking force to optimum level

Troubleshooting: Base Jaw Breakage

1. Component  Clamping at end of the stroke -Clamp the component at the middle of the Jaw stroke.
2. Excess Draw Bar pull (causing breakage of Master Jaw & Wedge) - Select suitable cylinder from ‘Selection Chart’ specified in GMT Instruction Manual and maintain the Draw Bar pull as specified.

Chuck Lubrication: What can go wrong if ignored?

What if you don’t lubricate as per schedule and don’t use the right lubricant?

 Improper lubrication results in;

• Loss of Gripping Force
• Component Slippage
• Clogging, restricting lubricant flow and Jaw Stroke
• Corrosion  

If the chuck is not lubricated regularly, the chuck body, wedge and the sliding parts will get corroded, resulting in high friction and loss of clamping force. The curve of the clamping force of a new lathe chuck, depending on the RPM, shows as a continuous curve. An improperly lubricated lathe chuck, shows a considerably reduced clamping force and shows as a dashed curve. This result in unsafe clamping of the work piece and the chances of falling out during machining is high. To avoid this, follow the lubrication and maintenance instruction provided in the chuck instruction manual. 

GMT recommends you to slide the master jaw through full stroke (clamping and de-clamping) to ensure uniform distribution of grease on sliding surfaces several times, without the component, after 500 jaw cycles. This helps to convey the lubricant to the sliding faces and maintain the clamping force longer.

For lubricating the lathe chucks, GMT recommends one of the following grease:

·         OKS  265            

·         ALTEMP  QNB50

·         MOLYKOTE  TP42

GMT chucks are equipped with several lubrication nipples for even application of grease. To ensure  even distribution of the grease inside the chuck, slide the master jaw through full stroke (clamping and de-clamping).

Remember, in extremely contaminated environment such as machining C.I work pieces a chuck can lose clamping force. In such cases, the complete chuck has to be disassembled, cleaned and lubricated. 

Chuck  with improper or no lubrication causes corrosion as shown in the photos below

                                                 CHUCK BODY                       BODY SLOT

                                                  WEDGE                                    BASE JAW

Write to us at esales@gmt.co.in for a free electronic copy of GMT Instruction Manual or visit our website www.gmt.co.in for more information