Even though a machine tool spindle is a high-precision machine component, more often than not it is handled carelessly, forced to perform well beyond design limitations, or otherwise abused to the breaking point. Proper care and maintenance can make all the difference in both its operation and longevity in service.
While most spindles in use today serve as high-precision machine components, it turns out that more often than not they are not treated with proper care and attention. Users sometimes may handle a machine tool spindle carelessly, force it to perform well beyond design limitations, or otherwise “abuse” the equipment to the breaking point and, as a result, good spindles will go bad. Proper care and maintenance of spindles ultimately can make all the difference both in operation and longevity in service.
Spindles are complex systems that integrate dozens of parts critical to machine tool performance. Some of these parts will typically require more care than others. For starters:
Rotating parts. These include shafts, rotors, spacers, nuts, encoders, coolant unions, flingers, drawbars, cutting tools, chucks, and quills, among others. All are critical. Tolerances for most of these rotating parts are held within millionths of an inch, which underscores that even slight mishandling can cause a spindle to perform below the standards established when it was manufactured or repaired (and premature failure may follow). By all means, rotating parts should never be hit, dropped, hammered, pried, pushed, or pressed.
Non-rotating parts. These, too, should be handled with care and inspected routinely. They include a spindle’s housing outside diameter, housing faces, flanges, caps, and oil and coolant ports. Problems with any one can cause associated problems down the road.
Main housing. Other parts of the machine in which the spindle serves are equally critical in delivering optimized performance. For example, a typical vertical machining center features a main housing to fit the spindle cartridge. This housing should be scrutinized regularly for signs of trouble. The inner diameter should be clean without signs of scoring or serious wear and the faces should not exhibit damage, nicks, or dings. In addition, the main housing to the machine should always be properly aligned; otherwise, spindle problems attributed to misalignment could develop.
Once a spindle is up-and-running, proper maintenance can help achieve desired long-term usage and lengthen MTBF (mean time between failure). Here are some tips of the trade for proper care and maintenance:
• Use the correct and filtered oil for the particular spindle. Supplying the right lubricant in the right amount at the right time is essential. Lubricant should always be high quality, properly specified and stored for the application, and clean and free from moisture or other contaminants. Neither too much nor too little lubricant should be applied and lubricant containers and all transmission lines should be inspected to rule out pre-existing contaminants.
• Maintain the proper airflow with clean, dry air. (Dessicant drying systems for compressed air represent a best practice.)
• Keep an eye on any leaks or pressure drops in the air/oil lines.
• Always break in a spindle for a few minutes if it has been idle for an extended time.
• Keep motor coolant clean and check for proper flow.
• Never over-cool the coolant when a chiller is used. This can cause condensation within the spindle or contraction of materials that can change the preload on the spindle’s bearings and likely lead to premature failure.
• Keep the coolant for the cutting tool directed at the cut as much as possible to eliminate (or at least reduce) potential backsplash to the spindle.
• Keep machined material from building up around the spindle. Otherwise, over time, problems will follow.
• Keep the working end of the spindle dry and clean. The inner diameter taper on a typical milling spindle sometimes may allow material being machined to get caught between the tool and the taper interface. This can result in damage both to the spindle and the tool holder.
• Store any spare spindles in temperature-controlled and clean areas.
• Rotate spindles by hand every few weeks if they are stored for an extended time. This practice can prevent oil and grease from sticking and creating other problems.
Machine tool spindles perform as ideal solutions to rotate cutting tools, grinding wheels, or parts to be machined in applications ranging from milling, drilling, and boring to grinding, cutting, and sawing. And, as with any critical asset, proper care and maintenance can go a long way toward preventing problems and avoiding unscheduled downtime and lost productivity.
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