Question regarding SFPM for Okamato 32-80EC
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  1. #1
    Join Date
    Sep 2015
    New York
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    Default Question regarding SFPM for Okamato 32-80EC

    Okay, so we are changing the wheel on this large surface grinder.

    We have always had a certain RPM set on the machine and it never changes. I think we can do better by adjusting for wheel wear etc.

    So, right on the very face of the machine in large print is "CAUTION: MIN SFPM 8125", and elsewhere maximum 9750.

    Easy enough.

    The machine is fit for a 16" diameter wheel, the max for the wheel.

    The formula for SFPM is (diameter x pi x RPM) / 12, and online calculators from Norton confirm this.

    Therefore, for a 16" wheel the spindle RPM should be around 1940 RPM.

    The problem? Our spindle speed adjustment goes from 0 to 2400 RPM, and right out of the gate on a brand new wheel its almost topped out. As the wheel decreases in diameter from where we actually can't spin it fast enough to maintain the safe minimum SFPM.

    Another problem? Right on the side our of brand new wheel is a message saying do not exceed 2030RPM, which is very close to the RPM needed to maintain the minimum SFPM.

    What am I missing here? Are the tolerances really that close? Within a few weeks of heavy grinding we'd have to either run under the min SFPM or exceed the RPM rating of the wheel.

    Any help or resources would be great.

  2. #2
    Join Date
    Aug 2005
    Raymond , CA
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    The old school standard for glass bonded aluminum oxide grinding wheels is 6000 feet per minute. There is a strong incentive to run at higher surface speeds whenever possible to reduce part grinding time, reduce wheel wear , and to minimize stress in the surface of the work piece. Modern machines and metal cored grinding wheels are designed to run in the 12000 feet per minute range and in some cases as high as 18000 feet per minute.

    You are using a old school grinding wheel. It would be best to recognize its limitations. I suspect your surface grinder had at one time a metal cored CBN wheel installed on it. That would explain the 8100/9700 sfpm minimum/ maximum speed label on the wheel housing.

    Keep in mind that the wheel balancing requirements are more demanding at the higher wheel speeds and your wheel guard needs to be designed to dissipate the energy released when a wheel fails. The coolant nozzle design may also need rework to be effective at higher wheel speeds.


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