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Problem-Solving Spindle Repair Boosts Machine Reliability

Oct. 21, 2021
Going beyond part replacement can optimize CNC machining, cost-effectively improving finished-part quality and shop productivity.

Because CNC machine tool spindles are essential to any drilling, milling, boring, grinding, routing, cutting, or sawing process, many manufacturers and machine shops rely on rebuilders to get production back online as quickly as possible when problems arise, and replacement is required. However, rebuilding a spindle is not always as simple as shipping off a problematic unit to have its parts replaced.

Every industry and shop floor has specific, even unique factors that require specific repairs, involving the materials machined, cut depths, required speeds, volumes, and precision for a range of applications. Failing to take these factors into account can lead to a host of unresolved issues that can degrade quality, consistency, and productivity.

At times the problems can be subtle such as intermittent variability or a faint sound indicating an issue that even a routine rebuild will not sufficiently resolve. Sometimes the problem can be serious and immediate. That is when additional expertise is required.

To cost-effectively ensure superior outcomes for challenges the best spindle repair shops will provide a true problem-solving approach. This includes understanding all requirements of the application, consulting with the machine shop operators, and even applying some expert detective work.

“The goal is to machine high-precision parts as soon as possible at the facilities I oversee. Because our operators run spindles at very high speeds, very fast, I need to be a problem-solver and I want to work with [spindle rebuilder and] repair shops that can solve problems,” said Eduardo Flores, maintenance manager at GAMMA Aerospace, a specialized, end-to-end provider of engineered airframe and flight components for leading original equipment manufacturers and Tier I aerospace and defense suppliers.

Problem solving boosts profitability. GAMMA Aerospace’s operations in Mansfield, Tex., Gardena and Los Angeles, Calif., and Mexicali, Mexico manufacture a diverse offering of components using advanced, in-house special processes that encompass machining, forming, assembly and wet chemical special processing.

As the maintenance manager of two plants, Flores oversees the use of about 50 CNC machines in Gardena and about 35 in Mexicali. His role is to keep the two shops running efficiently and involves ordering parts, troubleshooting, and problem solving.

According to Flores, optimizing spindle reliability including repairs and rebuilds is the “bread and butter of the business,” even when using softer metals like aluminum.

While diligently following preventative maintenance schedules for the CNC machines, Flores seeks expert help when concerns emerge. “Once the spindle starts giving us individual problems – that is not something I specialize in – so I consult with experts, because I cannot fix everything despite my best efforts,” he said.

According to Flores, one CNC machine brand had an unusual situation in which the spindles on some units lost orientation.

“This was something we didn’t hear and didn’t see on the controller. We just saw the result when it was trying to do an automatic tool change. With the wrong orientation the automatic tool changer would jam,” Flores explained. “The spindle certainly wasn’t bad; it was spinning correctly. It was just flipping on the orientation; it was an OEM defect.”

Neither the spindle manufacturer nor the CNC machine OEM could offer any help, so Flores turned to MZI Precision of Huntington Beach, Calif., an experienced machine tool spindle rebuilder. He consulted with Ed Zitney, president of MZI Precision who has about three decades of industry experience.

“When I consulted with Ed, he came over, observed the machine and saw that it was slipping. He took the spindle and created a retrofit for it,” Flores recalled.

Zitney reported that in such cases a spindle would lose its location in reference to the tool changer, which is typically a proximity switch issue. “We tested the proximity sensor, examined the location settings, the gap, and looked for any damage on the spindle’s pickup diameter or on the sensor,” he said.

“We discovered that all the proximity components were in good working order, but that on this particular model of spindle the compression rings were not capable of holding the coupling 100% in place. It would turn slightly, causing the machine controls to see a loss of positioning,” Zitney detailed.

Using only OEM components, MZI Precision engineered four special pins that locate and lock the coupling in place. This eliminated the movement and solved the issue of the machine faulting out because of the lost position.

According to Flores, the retrofit quickly and cost-effectively resolved the spindle problem, facilitating tool changes. “The engineered pins lock the spindle in place. It does not slip and lose its orientation, so tool changes are easy,” Flores said, pointing out the significant impact to production and the bottom line.

“Purchasing a new spindle would have cost us ten thousand dollars, plus about a thousand dollars to expedite it by air freight from Taiwan – and it may not have solved the problem because this was an OEM design issue,” Flores said. “For the same reason, a rebuild alone probably would not have resolved the problem. Working with an expert [MZI Precision] we ended up saving thousands of dollars per machine for a critical retrofit that will help us keep six CNC machines operating reliably going forward.”

Solving a mystery. While CNC machining is all about high precision and high production, equipment defects and anomalies may demand a singular, problem-solving approach to track down the source of a problem and correct it.

“We cannot afford to have a CNC machine not producing with unscheduled downtime,” according to Jon Welci, production manager at a Southern California location for Lexani Wheel Corp, a global manufacturer of custom luxury wheels.

Welci currently oversees about 15 CNC machines in his shop, and most are relatively new. When MZI Precision rebuilt the spindle of an older machine to OEM specification, however, a few days after installation the grease had mysteriously washed out of the bearings, threatening the machine’s reliability.

When MZI Precision investigated onsite its technicians found that the vertical milling spindle was driven by a gearbox filled with oil, and oil from the gearbox had overflowed into the top end of the spindle.

“The spindle design did not have a proper seal to restrict the oil from entering the spindle, so the oil displaced the bearing grease. The bearings ran very hot in the oil and would burn up very quickly,” Zitney recalled.

He noted that the fix was to engineer and manufacture a new top end cover/slinger. This new part covers the top end of the spindle and rotates with the spindle, preventing oil from entering the spindle’s top.

For even greater reliability and performance, at MZI Precision’s recommendation Welci ‘s shop upgraded to ceramic hybrid bearings in the spindle. With the engineered changes and the upgraded bearings the problem is solved. In fact, the spindle is actually far better outfitted for reliable performance than the OEM supplied unit.

“The CNC machine now works great. The increased reliability and performance make a big difference in our business,” Welci concluded.

When manufacturers and machine shops attempt to achieve a little more production uptime, precision and performance from their CNC machines, relying on a partner with deep spindle expertise can be the difference that increases their competitiveness and profitability.

Del Williams is a technical writer based in Torrance, Calif. He writes about health, business, technology, and educational issues, and he holds an M.A. in English from C.S.U. Dominguez Hills.

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