Belt Speed Calculator for 2x72 Belt Grinders

The industry standard to measure belt speed is SFM (Surface feet per minute). There is just one problem with that, to the regular Joe that doesn’t mean much because he can’t relate as he has no idea how fast it is. But if you give him the same value in MPH (Miles Per Hour) he will immediately relate because he has a reference point of how fast or slow that is because he drives his truck (or car for those who don’t have trucks) at 60 miles per hour every day and would think, wow that is fast. Just imagine sticking out my hand while driving and touching the belt at 60 miles per hour, this will take off some serious metal.

Belt Speed Questions

Belt Speed SFM vs MPH
The industry standard to measure belt speed is SFM (Surface feet per minute). There is just one problem with that, to the regular person, SFM has no meaning. But if you give him the same value in MPH (Miles Per Hour) they will immediately know what you are talking about.
What is the Ideal Belt Speed?
If you are new at knife making and can't afford a VFD then the best place to start is between 40 to 60 MPH. for most knife makers that is the ideal speed. Use the calculator to select the right drive wheel and motor combination for your 2x72 belt grinder.

With that said, there are many factors that come into play when determining the best belt speed such as:
  • The Material you are grinding such as Metal, Wood, Leather, etc.
  • The grit of the belt you are using.
  • The quality of the belt all manufactures are not the same.
  • The finish you are trying to get, higher grit sanding belts are used for polishing and will typically get you a better smother shinier finish.
  • Lower grit belts are used for removing material to shape the knife or whatever you are grinding and will give you a rough finish
    • What Size Drive wheel should I purchase?

    Buying your first grinder is always fun, the best target speed is between 40 and 60 MPH.
    It depends on your electric motor's speed. Use the calculator to determine the size of your "Drive Wheel" once you know your target speed, here are a few examples

    Belt Speed with 4" Drive Wheel

    1200 RPM - With 4" Drive Wheel = 14 MPH (Best for Small Wheels and knife sharpening)
    1800 RPM - With 4" Drive Wheel = 21 MPH (Okay for Small Wheels and knife sharpening)
    3450 RPM - With 4" Drive Wheel = 41 MPH
    3600 RPM - With 4" Drive Wheel = 43 MPH

    Belt Speed with 5" Drive Wheel

    1200 RPM - With 5" Drive Wheel = 18 MPH
    1800 RPM - With 5" Drive Wheel = 26 MPH
    3450 RPM - With 5" Drive Wheel = 51 MPH (Best Option for general Grinding)
    3600 RPM - With 5" Drive Wheel = 53 MPH

    Belt Speed with 6" Drive Wheel

    1200 RPM - With 6" Drive Wheel = 21 MPH
    1800 RPM - With 6" Drive Wheel = 32 MPH
    3450 RPM - With 6" Drive Wheel = 61 MPH
    3600 RPM - With 6" Drive Wheel = 65 MPH

    Belt Speed with 7" Drive Wheel

    1200 RPM - With 5" Drive Wheel = 25 MPH
    1800 RPM - With 5" Drive Wheel = 37 MPH 
    3450 RPM - With 5" Drive Wheel = 72 MPH
    3600 RPM - With 5" Drive Wheel = 75 MPH

    What is the formula to calculate Belt Speed?

    The formula to calculate SFM (Surface feet per minute) which is the same as Belt Speed is as follows:



    The higher the RPM or the larger the drive wheel the faster the belt speed.

    The Perfect Motor RPM and Drive Wheel Combo
    See the previous FAQ where we discuss the Drive Wheel size in more detail.




    This is what Wikipedia has to say about

    Surface Speed Per Minute – SFM the industry standard is defined as the number of linear feet that a location on a rotating component travels in one minute. Its most common use is in the measurement of cutting speed (surface speed) in machining. It is a unit of velocity that describes how fast the cutting edge of the cutting tool travels. It correlates directly to the machinability of the workpiece material and the hardness of the cutting tool material. It relates to spindle speed via variables such as cutter diameter (for rotating cutters) or workpiece diameter (for lathe work).