Spindle Contamination: Preventative Maintenance & When to Repair

1. Dust & environmental debris
   In the normal course of operations, environmental contaminants such as dust, lint, sand, and dirt can infiltrate spindle components, soiling lubricants and causing operational issues.
2. Chips
   Metal chips generated during machining processes can lead to premature failures if they enter the bearings.
3. Improper lubrication
   Using the wrong lubricant or neglecting lubrication can result in bearing seizures and poor spindle performance.
4. Liquid contamination
   This could come in the form of coolant or cutting oil/lubricant. Dirty coolant affects both bearings and the overall functionality of the spindle, which can lead to spindle failure. Coolant or cutting fluid that enters the spindle motor can also wash out the lubrication or short out the wiring.
5. Air supply contamination
   Improper air hose usage can lead to both liquid contamination and dust/chips, since the air can push contaminants into the spindle. This is of particular concern if the air supply for the contamination prevention system is not dry. Usually called an air purge or air knife, many systems use positive air pressure to deter contamination of the spindle. However, if the air is not sufficiently dried, it can cause rust and other contamination from moist or dirty air.

It’s impossible to keep a machining facility or worksite completely free of contaminants. However, it helps to know where contaminants come from so that you can take preventative measures.

• Unclean work environment / job site: Dirty surroundings, such as clogged air filters or a shop floor that has not been swept in a long time, can introduce contaminants to your equipment.
• Incorrect lubrication: This applies only to spindles that are lubricated by an oil delivery system. It’s important to consult the OEM manual to confirm the type of lubricant you can use with your spindle, as using the wrong lubricant or neglecting lubrication altogether can lead to contamination and eventual spindle failure. However, it should be noted that not all spindles require lubrication maintenance (i.e. “grease for life” spindles).
• Design flaws in the spindle: Some OEM designs may be more susceptible to contamination if not properly maintained.
• Improper assembly and testing: Units that are not assembled correctly or subjected to rigorous testing may be more prone to contamination.
• Lack of preventative maintenance: Neglecting regular maintenance allows contaminants to build up over time, which can cause permanent damage. A regular maintenance schedule can avoid issues by preventing contaminant build-up.

Contamination can cause a wide variety of problems, ranging from cosmetic to catastrophic. Common issues include:

• Poor parts finish
• Corrosion of components
• Diminished spindle lifespan
• Excessive/unplanned downtime

Any one of these issues can result in thousands of dollars in lost revenue and costly repairs that could have been avoided. Identifying and addressing contamination promptly is crucial for maintaining optimal spindle health and ensuring cost-efficient operations.

It’s not always apparent when an issue is caused by spindle contamination, which is why it’s important to understand the troubleshooting process before bringing in a repair expert. Signs your spindle may be suffering from contamination include:

• Poor surface finishing: Parts may display chatter marks, appearing as ripples or stripes in the metal.
• Out-of-spec products: The resulting dimensions, taper, etc. on a product may not match the customer’s specifications, despite proper machine programming.
• Excessive vibration: Some vibration is normal in most machining processes, but you will know it when you see, hear, or feel abnormal vibration.
• Excessive noise: Similarly, some amount of noise is normal, but any abnormal or increase in spindle noise can indicate contamination.
• High temperatures: Heat is another normal byproduct of machine operation, but it’s important to know a machine’s normal temperature range to identify potential anomalies. A spindle chiller may alert you to changes in temperature.
• Fretting: Wear on the spindle itself will present either visually or by bellmouthing — when the spindle’s taper is so worn down that the tool holder can sometimes rattle in the taper.
• Runout: Spindle runout occurs when a spindle no longer rotates on its intended axis, often evidenced by poor surface finish. Runout can either be a symptom or cause of contamination, since it can also result in excessive chip load.
• Dropping drawbar force: If your spindle drawbar’s pull force appears to be weakening, contamination may be the culprit. It may be possible to have only the drawbar serviced (avoiding the cost of sending away the entire spindle), so check with your preferred spindle repair facility.
• High load: If the motor load starts to increase on the machine readout, the source may be additional resistance caused by contamination.

To prevent contamination in your spindle, check the following:

• Ensure coolant spray is not aimed directly at the spindle nose.
• Turn off coolant spray when the spindle is not in operation.
• Keep coolant clean and maintained regularly.
• Avoid using compressed air around the spindle nose during cleaning to prevent blowing particles into the spindle nose.
• Maintain seal systems properly; for example, an air seal should produce filtered, dry air, and a contact seal should be re-oiled as needed.
• If using an air seal, keep the air flowing until the spindle has cooled to prevent a vacuum that sucks contaminants into the bearings.
• Verify that labyrinth seals have functional drains and that coolant is not directed at drain holes.

The type of seal can also impact contamination, as some seals are better at preventing contamination than others in certain scenarios. Common types of spindle seals include:

• Contact seals: Also known as lip seals, contact seals usually consist of a flexible lip that makes contact with a rotating surface. They help prevent the ingress of contaminants, such as dust, chips, and liquids, into the spindle. They are commonly used in areas where the sealing requirements are relatively moderate.
• Labyrinth seals: These are non-contact seals that use a series of closely spaced grooves to deter contaminants. This design helps to impede the entry of particles while allowing some axial movement. Labyrinth seals are often used in high-speed machining applications where friction and heat need to be minimized.
• Air sealing systems: Air seals use a continuous, controlled flow of clean, dry air to create a positive pressure barrier that prevents contaminants from entering the spindle. Air sealing systems are particularly useful in environments where the risk of contamination is high.
• Custom seal systems: Specialized sealing solutions can be tailored to specific machining applications to optimize sealing performance based on the unique needs of the spindle and the machining process. Custom solutions may involve a combination of different seal types or the modification of existing seals to meet unique requirements.

Implementing a regular spindle maintenance program is the key to saving potentially hundreds of thousands of dollars in repairs, replacements, downtime, and — worst case scenario — damages to people or property due to a malfunctioning machine component.

If you don’t already have a spindle maintenance program in place, use prior documentation of issues as a starting point to draft a predictive maintenance plan. However, when drafting up a maintenance schedule, be sure to allow for anomalies such as unforeseen machine issues or unexpected interruptions to operations.

Having seen thousands of spindles come through our doors, the technicians at Northland Tool & Electronics have encountered (and repaired) nearly every type of spindle issue. We’re well aware of the issues caused by contamination and can recommend preventative measures based on your application. We’re also on call for spindle emergencies, should it ever come to that — but hopefully, your preventative maintenance program will be so robust that spindle issues are few and far between.

To see the full breadth of our services, explore our Spindle Repair options, or give us a call for more information today.