Exposing the myth that all aerospace spindle rebuilds are equal

For aerospace manufacturers, CNC machine tool spindles are critical to any drilling, milling, boring, grinding, routing, cutting, or sawing process. However, when these systems deteriorate and fail due to contaminants, human error, improper maintenance, lubrication issues, or poor spindle design, a quality rebuild is often required.

Despite the availability of aerospace spindle rebuilders nationwide, not every firm provides the same level of quality. Even a rebuilder that has the equipment may not have the experience, technical knowledge, or attention to detail necessary to rebuild a spindle that performs reliably for many years.

Even reputable rebuilders vary in the extent and quality of the initial inspection, accuracy of quotes, and level of communication with customers. Given the direct correlation between these factors and the ultimate quality and longevity of the rebuild, most machinists continue to believe that it makes little difference which shop they contact.

In actual practice, however, the difference can be significant and seriously impact shop productivity. As a result, most machinists can easily relate tales of failed spindle repairs that led to costly downtime.

Credit MZI Precision

“After one spindle rebuild, I had to pull the machine out of production within a short time for additional repair,” says Tom Collins, maintenance supervisor at Edro’s Engineering’s Walnut, California facility. Edro Engineering, which serves North America and Europe, is a one-stop tooling solution shop for machining services, special materials, custom mold bases, PVD/DLC coatings, and additive manufacturing.

“Any time these CNC machines are down it costs us money, so we never want them down,” explains Collins, who is responsible for more than 50 milling machines, jig borers, and surface grinders. “Because we run our spindles often at high speeds and we do surface grinding of stainless steel and specialty materials, frequent rebuilds are necessary – even expected.

“So, if we send out a spindle and it is not properly repaired, it has to be removed again for additional repairs and that is going to put the machine down for even more time – and that’s even more money,” he adds.

Morgan Stipp, who supervises a grinding operation for Embee Processing in Santa Ana, California, agrees that minimizing downtime is essential.

Credit: MZI Precision

Stipp oversees about 20 precision grinders at Embee Processing’s 124,000ft² metal finishing campus facility in Santa Ana, California. This includes Studer CNC grinders, Okamoto NC OD grinding machines, centerless grinders, and other equipment with thread, surface, and superfinish grinding abilities.

Most part configurations require the chrome or high velocity oxygen fuel (HVOF) surfaces to be ground, polished, honed, and deburred after plating to achieve the desired surface finish. These operations are performed to ensure a flawless finish with tolerances as low as 50 millionths of an inch, according to Stipp.

“We are extremely picky with our precision grinding because it has to be essentially perfect for our customers. Without the right equipment and properly maintained spindles, we would not be able to stay in business,” Stipp says.

Stipp believes the thoroughness of the initial inspection performed by the repair/rebuild shop not only impacts the longevity of the spindle after it is rebuilt, but also the accuracy of the price quote.

“Having a machine down for unexpected extra maintenance because the inspection missed something can cost us a lot of money,” Stipp says. “We also do not want any surprise upcharges either, due to the original inspection and quote not being thorough enough.”

Both Stipp and Collins found the precision and attention to detail they required when they contacted MZI Precision of Huntington Beach, California, an experienced machine tool spindle rebuilder with a complete process to supply customers with a fast way back to maximum productivity.

While most aerospace spindle rebuilders only take minimal time to wipe parts before inspection, during disassembly the rebuilder cleans and polishes each component with emery cloth to clearly reveal even minute imperfections. Even the nuts are removed, polished, and then tested to ensure proper fit.

Credit: MZI Precision

The next step is detailed measurement and documentation of every part of the spindle’s shaft and housing geometry. Micrometers are used to take detailed size measurements, and runout is checked using 50 millionths of an inch dial indicators. The shaft bearing shoulders are then checked to see that they are true and perpendicular. The housing bores are checked for size, alignment, and shoulders squareness. MZI Precision also takes video, followed by digital photographs, of each part during the disassembly process.

“If I have anything go wrong with our spindles, I will call them before the manufacturer. They will diagnose the spindle at no cost and send me a detailed quote, which has been down to the penny on everything. I’ve never had a surprise charge,” Stipp says.

According to Edro Engineering’s Collins, the quality of the repair is also impacted by the expertise of the rebuilder and level of communication, traits he also found in MZI Precision.

“Communication is important, and it is a two-way conversation,” Collins says. “The company wants to understand how the spindle is run, the conditions, the types of parts being made, what metals are cut, the depths of cuts, etc., so the rebuild can be tailored to my application. Also, when I have a question, they answer it quickly.”

Collins also appreciates the spindle rebuilder’s use of only high-grade replacement components and bearings, which help to increase equipment reliability and lifespan. The rebuilder uses aerospace-grade bearings that are ABEC rated 7 or 9, the highest classification. Depending on the requirements, ceramic bearings are often recommended despite the nominal additional cost, due to longevity and higher running speeds.

“I have found their rebuilds to be as good as original equipment manufacturer (OEM) and sometimes better. The spindles have run perfectly so I expect them to last a long time,” Collins adds.

While spindle rebuild reliability and lifespan is essential, quick turnaround is also important since equipment downtime must be minimized. “The turnaround for our spindle rebuilds has to be timely to keep our production on track,” says Collins.

Although aerospace spindle rebuilds are available from various sources, for manufacturers that seek greater production reliability, uptime, and lifespan out of their CNC equipment, working with an expert spindle specialist is usually the best option.

MZI Precision

About the author: Del Williams is a technical writer based in Torrance, California.