Exposing the myth that all spindle rebuilders are alike

October 25, 2021 - 09:30pm

Expert spindle repair experts pay close attention to details.For 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 spindle rebuilders nationwide, not every firm provides the same level of quality. Even if a rebuilder has the equipment, they 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. Yet given the direct correlation between these factors and the ultimate quality and longevity of the rebuild, most machinist continue to believe that it makes little difference which shop they contact.

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

“After one spindle rebuild, I had to pull the machine out of production within a short time for additional repair,” said 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,” said 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 added.

The quality of the initial inspection matters when spindle repair work is involved.Morgan Stipp, who supervises a grinding operation for Embee Processing in Santa Ana, California, agrees that minimizing downtime is essential.

Stipp oversees about 20 precision grinders at Embee Processing’s 124,000-sq.-ft. 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 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 0.00005”, 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,” said Stipp.

In this regard, Stipp said he 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.

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 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.

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, runout is checked using 0.00005” 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 have never had a surprise charge,” said Stipp.

According Collins, the quality of the repair is also impacted by the expertise of the rebuilder and level of communication.

“Communication is important, and it is a two-way conversation,” said Collins. “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.”

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 utilizes 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 OEM and sometimes better. The spindles have run perfectly so I expect them to last a long time,” said Collins.

While spindle rebuild reliability and lifespan is essential, quick turnaround is also important to minimize downtime. “The turnaround for our spindle rebuilds has to be timely to keep our production on track,” he said.

Although 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.

For more information, phone 714-475-4016 or visit mziprecision.com.

Related Glossary Terms

  • boring


    Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

    Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

  • gang cutting ( milling)

    gang cutting ( milling)

    Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.

  • grinding


    Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

  • jig


    Tooling usually considered to be a stationary apparatus. A jig assists in the assembly or manufacture of a part or device. It holds the workpiece while guiding the cutting tool with a bushing. A jig used in subassembly or final assembly might provide assembly aids such as alignments and adjustments. See fixture.

  • milling


    Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

  • numerical control ( NC)

    numerical control ( NC)

    Any controlled equipment that allows an operator to program its movement by entering a series of coded numbers and symbols. See CNC, computer numerical control; DNC, direct numerical control.

  • outer diameter ( OD)

    outer diameter ( OD)

    Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

  • sawing


    Machining operation in which a powered machine, usually equipped with a blade having milled or ground teeth, is used to part material (cutoff) or give it a new shape (contour bandsawing, band machining). Four basic types of sawing operations are: hacksawing (power or manual operation in which the blade moves back and forth through the work, cutting on one of the strokes); cold or circular sawing (a rotating, circular, toothed blade parts the material much as a workshop table saw or radial-arm saw cuts wood); bandsawing (a flexible, toothed blade rides on wheels under tension and is guided through the work); and abrasive sawing (abrasive points attached to a fiber or metal backing part stock, could be considered a grinding operation).

  • surface grinding

    surface grinding

    Machining of a flat, angled or contoured surface by passing a workpiece beneath a grinding wheel in a plane parallel to the grinding wheel spindle. See grinding.


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