What is the definition of "dwell"?
Also called spark-out, an intentional time delay during which the rotating tool remains in contact with the workpiece. Dwell is part of the infeed grinding process.

Learn more about dwell in the class Centerless Grinder Operation 260 below.


Abrasives Training


Class Information
Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Centerless Grinder Operation 260
Description:This class addresses how to perform common grinding operations on the centerless grinder, as well as methods for mounting and truing the grinding and regulating wheels.
Prerequisites: none
Difficulty:Intermediate
Number of Lessons:19
Language:English, Spanish
 
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Class Outline
  • Objectives
  • Centerless Grinding
  • Advantages of Centerless Grinding
  • Components of the Machine
  • Throughfeed and Infeed Grinding
  • Endfeed and Infeed-Throughfeed Grinding
  • The Regulating Wheel and Workpiece Rotational Speed
  • Angle of Inclination and Feed Rate
  • Detecting Grinding Wheel Imbalance
  • Balancing Methods
  • Detecting Grinding Wheel Cracks
  • Mounting the Grinding Wheel
  • Achieving Part Roundness: The Work Rest Blade
  • Maintaining Consistent Part Diameter: Work Guides
  • Selecting a Grinding Wheel
  • Truing a Grinding Wheel
  • Truing a Regulating Wheel: Truing Angle
  • Truing a Regulating Wheel: Offsetting the Diamond Dresser
  • Summary
  
Class Objectives
  • Describe the relationship between the three main components used in centerless grinding.
  • Describe advantages of centerless grinding.
  • Describe the components of the centerless grinding machine.
  • Distinguish between throughfeed grinding and infeed grinding.
  • Distinguish between endfeed grinding and infeed-throughfeed grinding.
  • Describe how the regulating wheel determines workpiece rotational speed.
  • Describe how the angle of inclination determines workpiece feed rate.
  • Identify proper wheel balance.
  • Describe various balancing methods.
  • Identify the spots on the grinding wheel that may be tapped during a ring test.
  • Explain how to mount the grinding wheel.
  • Identify proper positioning of the work rest blade.
  • Describe how various placements of work guides affect workpiece shape.
  • Describe factors that assist in selecting an appropriate grinding wheel.
  • Describe various systems used to true a grinding wheel.
  • Describe the purpose of the truing angle.
  • Describe the purpose of offsetting the diamond dresser.

Class Vocabulary

Vocabulary TermDefinition
abrasive grain A small, hard particle or crystal of abrasive material used to machine, grind, or finish a workpiece. The tensile strength of workpiece material determines the abrasive grain of the grinding wheel.
angle of inclination The angle formed as the regulating wheel swivels out to allow the part to pass by. The regulating wheel angle of inclination provides axial thrust that feeds the workpiece past the grinding wheel during operation.
angular-bed grinder A type of centerless grinder that uses the regulating wheel to rotate the part until the part reaches the desired speed. The part contacts the grinding wheel only after it has reached the desired speed.
automatic balancer A precision device that uses one of several methods, including gasses and fluids, to detect vibration. Automatic balancers are used to balance grinding wheels where exact precision in grinding is required.
axial Running straight, or linear, along or parallel to the axis of a workpiece. A workpiece must both have both rotational and axial movement to be properly ground during centerless grinding.
axis An imaginary straight line passing through the center of an object. During throughfeed grinding, the part moves along or parallel to its axis.
balance The process of making a wheel round or concentric. Balancing may be accomplished through several methods, including truing with a diamond dresser.
balancing stand A frame-like device on which a grinding wheel is placed to check for balance. The grinding wheel is first mounted on a mandrel.
bed The main foundation and supporting structure upon which the operating parts of the machine are mounted and guided. Centerless grinders typically have cast iron beds.
blotter A paper ring that helps buffer mounting pressures between the wheel and the flange. Blotters are often placed between flanges and the grinding wheel to help prevent damage caused by tightening.
center A hardened, pointed, cylindrical component used to hold the end of a workpiece by inserting its tip into a matching hole in the part.
centerless grinding A common grinding operation in which a cylindrical part is supported on a work rest blade and guided between a grinding wheel and a regulating wheel.
center-type cylindrical grinding A type of cylindrical grinding in which each end of the workpiece is mounted on a pointed bar, or center.
chatter marks Surface imperfections on the workpiece caused by vibrations of the grinding wheel. An out-of-balance grinding wheel can result in chatter marks.
chuck A device that holds a workpiece in place as it rotates. The chuck commonly has three or four jaws that can be adjusted to fit various sizes.
crush roll A hard grinding wheel used under pressure to improve the face of another grinding wheel and usually to add a special shape. A crush roll is part of the crush roll truing attachment.
crush roll truing attachment A system used to true a grinding wheel in centerless grinding. This system uses a crush roll that presses into the grinding wheel to maintain the wheel's profile and expose a new surface.
cylindrical grinding A common grinding process that holds a cylindrical part on each end and rotates the part as a grinding wheel is guided along its length. Centerless grinding is a type of cylindrical grinding.
diamond dresser A tool containing one or more diamonds used to remove material from the surface of a grinding wheel. Diamond dressers are often used to true grinding and regulating wheels used in centerless grinding.
dressing The removal of swarf, dull grains, and bonding material from a grinding wheel. Dressing sharpens the wheel.
dressing tool A device used to remove loading and sharpen a grinding wheel. It might consist of an abrasive stick, a single-point diamond, or other tool.
dwell Also called spark-out, an intentional time delay during which the rotating tool remains in contact with the workpiece. Dwell is part of the infeed grinding process.
dynamic balance The ability of a grinding wheel to come to rest only when it loses momentum. The wheel is mounted on a mandrel and rolled along a balancing stand.
end stop Device that halts or prevents workpiece motion once the workpiece is ground to a specified location and depth. End stops are used in infeed grinding and endfeed grinding.
endfeed grinding A method of centerless grinding in which the workpiece is fed into the grinding and regulating wheels until the workpiece contacts an end stop. Endfeed grinding is used to taper the end of a workpiece.
face In grinding, the part of the wheel that contacts the workpiece. The truing angle ensures that the workpiece makes a straight line of contact with the regulating wheel face.
feed rate The rate at which the grinding wheel and the workpiece move in relation to one another. The regulating wheel angle of inclination provides the axial thrust that determines workpiece feed rate.
feeding method The way in which stock or parts enter the point of operation on a machine. Centerless grinding uses an automated feeding method.
flange A flat or raised metal disk that helps deflect mounting stresses from the hole in a grinding wheel. The grinding wheel is typically mounted to the spindle using flanges.
friability The ability of abrasive grains to fracture and self-sharpen under stress. For centerless grinding, the workpiece diameter determines the necessary friability of the grinding wheel.
glazing The unwanted formation of a smooth surface on a grinding wheel. Dressing and truing a grinding wheel prevents glazing.
grade The strength of the bond in an abrasive wheel. For centerless grinding, the workpiece length determines the grade of the grinding wheel.
grinding wheel A wheel made of a bonded abrasive used to remove material from a surface by rotating and shearing away microscopic chips of material. Grinding wheels can produce very fine surface finishes.
horizontal-bed grinder The most common design of centerless grinders, a grinder that causes the part to rotate only after it touches the rotating grinding wheel.
infeed grinding Similar to plunge grinding, a method of centerless grinding in which the workpiece is held stationary while the grinding wheel is fed into the workpiece at a specified location and depth.
infeed-throughfeed grinding Used to grind workpieces with too much stock to be ground using throughfeed grinding, a method of centerless grinding in which the regulating wheel feeds the workpiece into the grinding wheel until a specified workpiece diameter has been ground. The end stop then moves away from the front of the machine, allowing the workpiece to pass to the front of the machine.
loading A build-up of swarf in a grinding wheel that clogs the spaces between grains. Dressing and truing a grinding wheel prevents loading.
lock nut A type of nut that screws down on top of another nut to hold the first one in place. Parts of a sleeve are held together with a lock nut.
lower slide The device that is attached to the swivel plate and moves the regulating wheel toward or away from the workrest blade.
mandrel The spindle or post on which a wheel is mounted. A wheel must first be placed on a mandrel to be tested for imbalance.
plunge grinding A type of cylindrical grinding in which the cylindrical wheel is fed perpendicular to the axis of the part. Infeed grinding is analogous to plunge grinding.
profile A specialized edge that is added to the face of a wheel to help it conform to a particular grinding operation or part shape.
profile truing attachment A system used to true a grinding wheel in centerless grinding. This system uses a diamond dresser to true a profile attached to the grinding wheel face.
regulating wheel A wheel, usually made of plastic or rubber bond, used during centerless grinding to rotate the workpiece and pull it through the operation. The regulating wheel controls workpiece rotational speed and feed rate.
regulating wheel housing The device that is mounted to the upper slide and houses the regulating wheel and regulating wheel spindle.
revolutions per minute RPM. Regulating wheel surface speed rate is measured in RPMs.
ring test A manual test used to detect damage in bonded grinding wheels. Operators suspend a wheel loosely and tap it with a tool. Wheels that emit a clear ringing sound rather than a dull sound are likely undamaged.
RPM Revolutions per minute. Regulating wheel surface speed rate is measured in RPMs.
sleeve A type of flange that fits together with two differently shaped parts and a lock nut.
spark-out Also called dwell, an intentional time delay during which the rotating tool remains in contact with the workpiece. Dwell is part of the infeed grinding process.
standard truing unit A system used to true a grinding wheel in centerless grinding. This system uses a diamond dresser to true the face of a grinding wheel for straight, cylindrical parts.
static balance The ability of a grinding wheel to remain at rest in any position when placed on a balancing stand.
stock Raw material used to make manufactured parts. The precision of centerless grinding enables the use of workpieces with less stock, which reduces wheel wear.
surface speed The uniform rate at which the regulating wheel revolves against the workpiece. Surface speed determines the work speed of the workpiece.
swivel plate The device that is mounted to the bed and tilts or aligns the regulating wheel parallel to the grinding wheel.
taper A gradual decrease in the width of an object. Endfeed grinding is used to taper the end of workpieces.
tensile strength A material's ability to resist forces that attempt to pull apart or stretch it. In centerless grinding, the tensile strength of the workpiece determines the abrasive grain of the grinding wheel.
through feed In grinding, the movement of a workpiece as it travels through an operation. For most centerless grinding operations, the regulating wheel is slightly angled to provide the part's through feed.
throughfeed grinding A method of centerless grinding in which the regulating wheel and work guides feed the workpiece past the grinding wheel in a straight line. Throughfeed grinding is used primarily to grind straight, cylindrical workpieces with no obstructive features.
true To restore a grinding wheel to its original shape. Truing is also a method of wheel balancing.
truing The dressing of a wheel in order to return the wheel to its original shape. Truing is also a method of wheel balancing.
truing angle The angle formed by the truing device that matches the regulating wheel angle of inclination. The truing angle creates a slightly convex regulating wheel face, which enables a complete line of contact between the regulating wheel and workpiece during centerless grinding.
upper slide The device that is attached to the swivel plate and moves the regulating wheel and workrest blade toward or away from the grinding wheel.
wheel balance A wheel that has equal weight and shape throughout, making it completely concentric. A balanced wheel does not vibrate.
wheel head The part of the grinding machine on which the wheel is mounted. On a centerless grinder, the wheel head contains the grinding wheel and grinding wheel spindle.
work guide A device used in centerless grinding that prevents the workpiece from moving too far toward either the regulating wheel or grinding wheel. Work guides help maintain consistent workpiece diameter.
work rest A part of a centerless grinding machine that supports the workpiece as it is ground. The work rest is mounted to the lower slide and supports the work rest blade.
work rest blade A device, usually with an angled edge, that supports cylindrical parts during centerless grinding. The above-center positioning of the work rest blade produces concentricity of the workpiece.
work speed The rotational speed of the workpiece. The work speed is approximately equal to the surface speed of the regulating wheel.