Grinding Wheels

We use grinding wheels to:

  • Size a part accurately;
  • Improve the surface finish;
  • Generate a surface with a specific shape.
  • Grinding operations are often performed on very hard metals.

What are they made from?

  • Grinding Wheels are normally hard and brittle.  They are made from one of these:
    • Aluminum Oxide: Used for grinding Steel
    • Silicon Carbide: Used for grinding cast iron, nonferrous and nonmetallic materials.
      • Friability: Aluminum oxide and silicon carbide are both very hard and brittle.  This “Friability” causes the grains to break easily.  During the grinding process, each broken grain reveals a new and very sharp cutting edge.
    • Diamond: Used for grinding cemented carbides, glass and ceramics.
    • Cubic Boron Nitride (CBN) (Borazon) (ABN):  Used for grinding hardened tool steels and superalloys.

Wheel Bonds

  • Grinding wheel abrasive is held together with one of the following bonding materials:
    • Vitrified – Inert and able to withstand high temperatures.
    • Resinoid – High operating speeds or loads.
    • Rubber – Flexible and for a high, burr free finish.
    • Metal – Base for the electro-deposition of diamond or CBN abrasive.

Grinding Wheel Shapes

  • Straight Wheel (Type 1)
  • Cylindrical Wheel (Type 2)
  • Flaring Cup Wheel (Type 11)
  • Dish or Type 12 Wheel
Grinding Wheel Shapes

Grinding Wheel Shapes

Wheel Identification

  • Five major factors are used to identify most grinding wheels:
    1. The type of abrasive
    2. The size of the grit
    3. The grade or hardness
    4. The Structure
    5. The Bond
  •  ANSI Standard B74.13-1990  Markings for Identifying Grinding Wheels & Other Bonded Abrasives
Markings for Identifying Grinding Wheels

Markings for Identifying Grinding Wheels

“Glazing” and “Loading”

  • A glazed wheel occurs when the abrasive grains are dull.  The cutting surface of the wheel appears shiny.
  • Loading occurs when foreign material becomes trapped in the voids (spaces) between the abrasive grit.
  • Dress the wheel when it becomes “loaded” or “glazed”.
  • The wheel at the top is “loaded”.  Bits of metal are embedded in its grinding face.  It is poor practice to off-hand grind soft metals like aluminum on a pedestal grinder. The same wheel, below, has been dressed to remove the “loading”.

Truing & Dressing

  • In a perfect world, a grinding wheel will be self-sharpening.  Dull grains will fracture or will be dislodged from the wheel surface, exposing new sharp cutting edges.  Unfortunately this is rarely possible.
  • Wheels need to be trued and dressed when mounted and must be dressed regularly thereafter.

Truing a Grinding Wheel

  • Truing a wheel ensures the outside cutting surface runs true with the machine spindle.
  • A wheel must always be trued after it has been mounted.
  • Truing a wheel on a precision surface grinder is normally accomplished with a single point diamond dresser.

Dressing a Grinding Wheel

  • Dressing a wheel exposes new cutting edges and improves the cutting action.
  • Wheels must be dressed regularly as required, using one of the following:
    • Rotating hand dressers
    • Abrasive sticks or wheels
    • Single point or cluster diamond dressers
    • Crush roll dressers

Single-point Diamond Dresser.

  • The most important precaution when using this dresser is to turn the diamond often to avoid grinding flats on it.  Take care not to subject the diamond to “Thermal Shock”.
  • One way of mounting a single-point dresser on a surface grinder. The dresser with its diamond is magnetically secured on a clean chuck. Note the diamond is slanted at a 15-degree angle and positioned slightly past the vertical centerline of the wheel.
Single-Point Diamond Dressor

Single-Point Diamond Dressor

Mounting Grinding Wheels

Mounting Grinding Wheels

Mounting Grinding Wheels

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