REPLACE OR REMANUFACTURE?

Given their demanding application requirements for high levels of speed, accuracy, precision, and repeatability, machine tools owe their life to the spindle, which can be described as the “heart” of the machine. But when the heart skips some beats or stops entirely, how best to make the fix? Replace the entire spindle outright or resuscitate and rejuvenate by remanufacturing? The appropriate course of action will ultimately revolve around the interrelated issues of time, money, and productivity.

Machine tool spindles, in all their designs and sizes, serve as highly advanced technology solutions that are essential to key operations on the shop floor. They are routinely used to rotate cutting tools, grinding wheels, or parts to be machined in applications ranging from milling, drilling, and boring to grinding, cutting, and sawing. Spindles stand as complex systems integrating dozens of components critical to machine tool performance.

As with any asset, however, defects can arise resulting in spindle breakdowns over time. The root causes of spindle defects may include crashes, overloads, coolant/contaminant penetration, normal fatigue, or others. No component is immune.

The effects of wear especially can bear down on spindle components. Those components typically subject to wear include the shaft; front, rear, and main housings; bearings; stator; rotor; finger assembly; drawbar springs; spacer; encoder, and front shaft nut and cap. Each plays a vital role.

While remanufacturing has always been an option, today’s economic climate makes a particularly compelling case. It is no longer a commonplace practice to automatically purchase a new spindle when one fails and, with potential reliability problems looming at every turn, it is perhaps unsurprising that spindle maintenance and refurbishment have been estimated to account for half of the worldwide machine tool market.

Turning to options other than outright replacement, spindle remanufacturing has made significant gains in the marketplace for a variety of practical reasons, grounded in the issues of time and money. A comparison of delivery lead times and the costs of replacement vs. remanufacture tell a compelling story.

If you are lucky, a new spindle may be in stock at your local dealer but, on average, the lead-time for delivery of a new replacement spindle can run as long as 24 weeks, while repairs or reconditioning can usually be made in less than two weeks (and, in some instances, even a few days). The price tag for a new spindle, too, sometimes can average as much as triple the cost of a remanufactured unit. Such numbers make a strong case supporting the remanufacturing approach.

Contributing to the bottom-line, the investment in remanufacturing will involve only the components that need to be replaced, bypassing the higher costs associated with purchasing an entirely new spindle. Spindles further can be remanufactured many times over without adverse consequences.

Of course, every shop will approach the decision about whether to replace or remanufacture guided by its own particular situation and requirements. The decision will depend, in part, on asking the right questions and arriving at the answers that make the most sense. How critical is the spindle to the operation? How much downtime from an off-line spindle can be reasonably absorbed? How will productivity be impacted? How will diminished workflow affect customer satisfaction, the shop’s response times and reputation, and overall profitability?

At least one additional question begs to be asked when considering how to deal with a defective spindle: Is there an opportunity to improve the performance or versatility of the existing spindle during the repair or reconditioning process? The answer is that spindles undergoing remanufacture represent prime candidates for customization or upgrades that can add value and expand application potential. Spindles can be customized or upgraded any time, but when a spindle moves into remanufacture, it usually makes economic (and timely) sense to seize the opportunity.

Depending on the spindle application, upgrades may be as simple as adding an air purge to keep the bearings and the inside of the spindle free of contamination, or replacing standard steel bearings with hybrid ceramic bearings to improve life or increase speed. Major upgrades can encompass multiple changes delivering newfound spindle capabilities. Customization can uniquely tailor a spindle to application demands.

When “good spindles go bad,” their replacement may be unavoidable. But, if not, remanufacturing can enable a relatively quick and cost-effective return to productivity.

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Edward Zitney, Jr., oversees SKF Machine Tool Services, a business unit of SKF USA Inc., www.skfusa.com. He has 29 years of experience in the repair, reconditioning, and upgrading of machine tool spindles and is responsible for SKF’s state-of-the-art Spindle Service Center in Mentor, OH, and the recently opened SKF Solution Factory in Houston, TX. For questions or comments on this column, Contact Ed at 800-589-5563 or Edward.Zitney@skf.com.