Idea Bulletin

Omnimills’ Spindle Upgrade Single, 25 hp, CAT 50 integrally-motorized spindle replaces two belt-driven spindles


A major aircraft engine manufacturer wanted to upgrade to the spindle on its OM-3 and OM-4 Sundstand Omnimills (5-axis machining centers with a 150 degree tilting head). Material being machined was inconel, titanuim and other aerospace alloys


Converting the original two- spindle arrangement (a low- speed spindle to handle large tools and a high-speed spindle for small tools) presented a number of challenges. A conventional rebuild would require a completely new slide casting together with a two- speed, timing, belt-coupled spindle cartridge requiring oil-bath bearing lubrication, a complicated design that would be both hard to adjust and maintain.



Instead of redesigning the head to accommodate a conventional belt-driven spindle, the machine builder suggested an integrally-motorized spindle for better functionality. Ultimately, the solution came in the form of a single 25 hp (18.6 kW) spindle, capable of 7,500RPM, with CAT 50 taper and through-spindle coolant. A stock spindle being unavailable, a Gilman engineering team visited the rebuilder to review the application. After research, the engineers recommened Indramat windings to fit within the severe space constraints ofthe head. A new head casting configuration, machined to allow coolant to circulate around the spindle body, allowed the spindle to drop into the housing and bolt through a flange, making spindle removal an under-30-minute job. To eliminate the problem of a hoseband moving with the tilt head, the housing is also inner-drilled and plumbed to handle all hydraulic, coolant, and electrical requirements.

Cost Savings

Redesigning and rebuilding the user approximately one half the cost of a new machine. Six machines have been converted to date.

Time Line

Total project time, from initial consultation to spindle delivery, was 18 weeks.

Technical Specifications

  • Spindle:

    •    Preloaded Triplex set ABEC 7, 25° hybrid ceramic angular contact ball bearings nose end (90mm I.D.)

    •    Preloaded pair ABEC 7, 15° angular contact ball bearings back end (70mm I.D.)

    •    Kluber NBU15 grease lubrication

    •    Inpro VBX seals each end

    •    Indramat encoder feed back for closed loop operation with Indramat drive

    •    OTT Hydraulic draw bar with coolant thru and taper air blast cleaning

    •    7,500 RPM maximum

    •    Maximum thrust into spindle 1,200 lbs.


    •    The spindle is driven by an Indramat intelligent AC vector drive. Stop and orient mode takes less than 3 seconds at 7,500 RPM. The rebuilt machine has a wide range of speeds without gear changes.


Every care has been taken to ensure the accuracy of the information contained in this publication but no liability can be accepted for any loss or damage whether direct, indirect, or consequential arising out of use of the information contained herein.

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