Gearboxes fail the way spindles do: gradually, then suddenly. Wear accumulates quietly, then shows itself as noise, heat, and oil where oil does not belong. And like a spindle, a worn gearbox can be rebuilt to run like the unit it was, which is usually the better bet than gambling on a replacement.
Signs a gearbox needs attention
Listen first. Gear noise that changes with load or speed is the classic early sign, and heat follows it. Then look at the oil: its level, its condition, and above all where it is going. Oil that keeps disappearing, or that turns up somewhere it should not be, is a gearbox telling you about its seals, and on machine tools that message can be expensive to ignore, because the thing next door is often the spindle.
The gearbox next to your spindle
MZI documented exactly that failure at a wheel manufacturer running about fifteen CNC machines. Days after an otherwise correct, OEM-spec spindle rebuild, the grease had washed out of the spindle bearings and they had run hot and burned up. The cause was not the rebuild. The vertical milling spindle was driven by an oil-filled gearbox, the design had no proper seal at the interface, and gearbox oil overflowed into the spindle’s top end and displaced the bearing grease. The fix was engineered, not swapped: a new top-end cover that rotates with the spindle to shed the oil, plus an upgrade to ceramic hybrid bearings. The result performed better than the original unit. The failure analysis guide has the full investigation.
That is why, on gear-driven machines, we treat the gearbox and its sealing as part of the spindle diagnosis rather than a separate subject. Fixing one while ignoring the other is how the same failure comes back.
What a gearbox rebuild covers
Gearbox rebuilding is a standing MZI service, alongside spindles and servo motors. The discipline is the one described across these guides: documented disassembly, failure analysis that names the real cause, inspection and measurement, a line-item quotation, and rework and assembly on your purchase order. Rebuilds can run alongside spindle work when both units are involved, which is common, or stand alone when the gearbox is the whole problem. The motors and gearbox pillar covers how the pieces fit together.
Frequently asked questions
Do you rebuild gearboxes on their own, or only with spindle work?
Both. Gearbox rebuilding is one of MZI’s standing services. Many gearbox jobs arrive alongside a spindle rebuild because the two units fail together, but a gearbox can come in on its own.
What are the signs a gearbox is failing?
Gear noise that changes with load or speed, rising heat, and oil problems: dropping level, degraded condition, or oil migrating somewhere it does not belong. On gear-driven machine tools, unexplained spindle bearing problems can also point back to the gearbox and its seals.
What does a gearbox evaluation cost?
The same as a spindle evaluation: nothing until you approve the work. Disassembly, inspection, failure analysis, and a line-item quotation carry no charge until a purchase order approves the rebuild, with rare exceptions for complex units, noted to you before any work starts.
Start with a phone call
Edward Zitney
President
(714) 475-4016
He has spent more than 44 years in spindle rebuilding and remanufacturing. He learned the trade over more than two decades at Precision Balancing & Analyzing, the shop long regarded in the industry as the standard for spindle work, later oversaw SKF Machine Tool Services, held service leadership roles at Setco, and wrote a published column on spindle remanufacturing for Fabricating & Metalworking.
Marco Guerrero
Partner
(949) 374-0060
He came up on the shop side of this industry. He started with his hands, welding and fabricating for the racing industry, then spent fifteen years as general manager growing a machining job shop, the same kind of shop that sends MZI spindles today. He has sold CNC machines too, so he knows what new equipment costs and when a rebuild is the smarter call. Today he and Ed are partners in MZI Precision, and his standard is simple: every customer feels informed and supported from the first call to the day the spindle ships back.
Call (714) 379-6505 and describe what changed. With a little information about your spindle we can diagnose the problem and determine your best action.
What to expect on the call:
- You talk directly with a spindle expert.
- Some problems can be diagnosed over the phone, and a few do not require removing the spindle at all.
- If your spindle should come in: disassembly, inspection, failure analysis, and a line-item quote, at no charge until your purchase order approves the rebuild.