Centerless Grinder Operation 253

alignment bar

A cylindrical setup tool that has a diameter that is the same as or slightly smaller than the workpiece diameter and extends beyond the width of the regulating wheel on both sides. An alignment bar, or test bar, is used to find the proper clearance between the work guides and the workpiece.

angle of inclination

The position of the regulating wheel spindle centerline in relation to the grinding wheel centerline. The regulating wheel angle of inclination provides axial thrust, which feeds the workpiece past the grinding wheel during centerless grinding.

angle of inclination

The position of the regulating wheel spindle centerline in relation to the workpiece axis. The regulating wheel angle of inclination provides axial thrust, which feeds the workpiece past the grinding wheel during centerless grinding.

automatic size control

An automated system that adjusts the grinding wheel when its wear adversely affects part diameter. Both stepping motors and magnetostrictive slide adjusting devices are automatic size control systems.

axial

Running straight along or parallel to the axis of a workpiece. Axial as well as rotational movement are required for a workpiece to be properly ground during centerless grinding.

back clearance

The intentional amount of space left between the back work guide and the workpiece during throughfeed centerless grinding. The back clearance on the regulating wheel side should be between 0.0004 and 0.0010 in. (0.0102 and 0.0254 mm).

bearing surface

The portion of a component that makes contact with the part. Bearing surfaces on centerless grinding work guides physically guide the part precisely onto the work rest blade and into the grinding zone between the grinding and regulating wheels.

beta ratio

β. A calculation that can be used to predict lobing conditions in centerless grinding. The beta ratio is a fraction equal to the grinding wheel speed multiplied by the workpiece diameter over the regulating wheel speed multiplied by its diameter.

bond

The material that holds abrasive grains together in a grinding wheel. Bond, or bonding material, can be vitrified, resin, rubber, or metal.

centerless grinding

A method of grinding cylindrical parts. Centerless grinding supports parts on a work rest blade and guides them between a grinding and a regulating wheel.

centerline

An imaginary line that runs through the center of a cylindrical object. A perfectly cylindrical workpiece, rotated on a perfectly flat surface or held in a perfectly concentric fixture, will rotate about its centerline.

chatter marks

Surface imperfections on the workpiece caused by forced vibrations. Chatter marks can occur when the work rest blade is positioned too high above the grinding and regulating wheel centerlines.

chattering

The occasional unwanted vibration between components. Chattering caused by kinks and bends in a part is known as forced chatter, while chattering caused by machine vibration is called unforced chatter.

circumference

The boundary or perimeter around a circle. Circumference measures the distance around a circle.

clearance

An intentional amount of space left between two components. Clearance for centerless work guides prevents the guides from blocking contact between the wheels and workpiece.

computer numerical control

CNC. A self-contained system of computers and precision motors that executes program instructions to guide machine tool components and manufacture parts. A computer numerical control machine automatically adjusts machine parameters without operator involvement.

concave

Hollowed out or curving inward. Concave spots last for only an instant on lobed parts before they are ground away to form a convex shape.

coolant

A liquid that helps to cool, lubricate, and clean swarf from grinding operations in the safest, most environmentally conscious way. Coolant, also known as grinding fluid, may be water-based, a straight oil, or even a liquid gas and may include synthetic chemicals, extra additives, oils, emulsifiers, dyes, and other ingredients.

deflect

To deviate from a straight line or plane when a force is applied. When a part deflects, incorrect measurements often result.

denominator

The number on the bottom of a fraction. The denominator in a beta ratio equals regulating wheel revolutions per minute multiplied by the regulating wheel diameter.

dresser

A tool made of diamond or metal that is used to remove material from the surface of a grinding wheel. Dressers are used to dress and true a grinding wheel.

dressing

Removing swarf, dull grains, and bonding material from an abrasive wheel by fracturing away the wheel surface. Dressing shapes and conditions the surface of the wheel to be open, sharp, and free-cutting or closed, smooth, and able to achieve a high dress of surface finish.

dwell

An intentional time delay during which the rotating grinding wheel remains in contact with the rotating workpiece and all radial feed is halted at a predetermined place. Dwell, or spark-out, allows for any machine and workpiece deflection to relax and results in consistent and precise size control.

end stop

A device that halts or prevents workpiece motion once the workpiece is ground to a specified location and depth. End stops are used in endfeed and infeed centerless grinding.

endfeed grinding

A method of centerless grinding in which the wheels are angled to match a workpiece taper. Endfeed centerless grinding uses an end stop.

equidistant

Of equal distance. If every point on the circumference is equidistant to the center of a circle, that indicates that the circle is round.

face

The part of a grinding wheel that makes contact with the workpiece. A regulating wheel face must be trued to maintain a straight line of contact with a workpiece.

feeler gage

A device used to determine if there is proper clearance between components on a machine. A feeler gage has one hinge on which several steel leaves of various measured thicknesses are located.

fraction

A number that indicates parts of a whole number. Fractions appear as one number over the other with a slash or horizontal line between them.

front clearance

The intentional amount of space left between the front work guide and the workpiece during throughfeed centerless grinding setup. Front clearance prevents contact with the bearing surface of the front work guides from inhibiting workpiece contact with the regulating wheel.

gamma angle

γ. The angle of the two tangential lines formed at the points of contact between a centerless grinding workpiece and each wheel. The gamma angle is also known as the roundness correction angle.

gearing action

A transfer of motion from one part of a machine to another. Gearing action in centerless grinding leads to lobing.

grade

A classification that describes the quality of a material. In grinding, the grade describes the strength of the bond in an abrasive wheel.

grinding

Using an abrasive to wear away a workpiece surface and achieve highly accurate measurements. Grinding operations commonly use abrasive grains bonded into a wheel shape.

grinding fluid

A liquid that helps to cool, lubricate, and clean swarf from grinding operations in the safest, most environmentally conscious way. Grinding fluid, also known as coolant, may be water-based, a straight oil, or even a liquid gas and may include synthetic chemicals, extra additives, oils, emulsifiers, dyes, and other ingredients.

grinding wheel

A wheel made of abrasive grains that are held together by a bonding material. A grinding wheel rotates and grinds away microscopic chips of material and can produce very fine surface finishes.

infeed grinding

A centerless grinding process in which workpieces do not move all the way through the machine. Infeed centerless grinding involves the regulating wheel and work rest pushing the workpiece into the grinding wheel.

infeed-throughfeed grinding

A centerless grinding process that functions like a throughfeed operation and removes large amounts of stock from long, straight workpieces. Infeed-throughfeed grinding uses an end stop.

in-process gaging

Inspection that measures part diameter during a centerless grinding process. In-process gaging runs automatically and alerts operators to variations in part diameter that require adjustment of the machine to avoid any out-of-tolerance parts.

lobe patterns

Two opposing ends of a circular part’s diameter where one end has a larger radius than the other end. With an incorrect setup, centerless grinding usually results in an odd number of lobe patterns around the periphery of a workpiece.

lobing

Deviation from workpiece roundness. Lobing is prevented by proper setup of the centerless grinder.

magnetization

A process by which a material becomes attracted to materials with opposite electrical charge. Magnetization most often occurs between ferrous metals that contain high percentages of iron.

magnetostrictive slide adjusting device

An automatic size control system that involves moving the grinding wheel slide by expanding the device's core using magnetization. This device usually moves the grinding wheel slide in 0.000050 in. (0.001270 mm) increments, though this increment can be larger or smaller.

manual machine

A machine that requires an operator to control various aspects of its operation. Manual centerless grinding machines require an operator to set and adjust component positions and other parameters.

meters per second

m/s. A metric speed measurement that indicates the number of meters that move past an object each second. Meters per second is a direct function of the workpiece or grinding wheel diameter and its rate of rotation.

numerator

The number on the top of a fraction. The numerator in a beta ratio equals grinding wheel speed multiplied by workpiece diameter.

out-of-round

An irregularly shaped circle that is not totally round. Many out-of-round conditions are caused by lobing.

out-of-tolerance

A deviation from a desired dimension that no longer meets specifications. Out-of-tolerance size dimensions most often occur in centerless grinding when the grinding wheel becomes worn.

periphery

The perimeter, or edge, of an object. Many types of grinding wheels grind with their periphery.

post-process gages

An inspection device used to measure part diameter directly after the centerless grinding process. Post-process gages run automatically and alert operators to variations in part diameter that require adjustment of the machine to avoid any out-of-tolerance parts.

radial difference

The difference between the radii of two cylindrical objects. A radial difference is calculated by subtracting the diameter of one object from the diameter of the second object and dividing the result by 2.

rate of traverse

The speed at which the dressing tool travels across the grinding wheel. The rate of traverse for a dressing tool is critical in order to achieve the desired condition on the surface of the grinding wheel and is best controlled by an electrical feeding mechanism.

regulating wheel

A grinding wheel commonly made of resin bond that is used to slow a workpiece's rotation against a centerless grinding wheel. A regulating wheel, or control wheel, also drives the workpiece axially across the work rest blade.

revolutions per minute

rpm. The number of revolutions that a spindle completes in one minute. Revolutions per minute is a measurement of speed in both English and metric systems.

rotational speed

The rate of rotational movement of the workpiece or grinding or regulating wheel. Rotational speed is measured in revolutions per minute (rpm).

rpm

revolutions per minute. The number of revolutions that a spindle completes in one minute. Rpm is a measurement of speed in both English and metric systems.

setup

The series of tasks necessary to prepare for processing a workpiece. Setup includes preparing machines, adjusting workholding devices or tooling, and safeguarding machine elements to ensure proper and safe operation.

slide

The component on a machine that conveys back-and-forth movement of other components. On a centerless grinder, the grinding wheel can have an optional slide, while the regulating wheel always has a slide.

spark-out

An intentional time delay during which the rotating grinding wheel remains in contact with the rotating workpiece and all radial feed is halted at a predetermined place. Spark-out, or dwell, allows for any machine and workpiece deflection to relax and results in consistent and precise size control.

stepper motor

A type of motor that can be used to position any machine axis using computer numerical control. A stepper motor may be used, with feedback from a post-process gage, to move the grinding wheel and automatically compensate for wheel wear.

stock

Raw material used to make manufactured parts. Stock is available in standard shapes, such as long bars, plates, or sheets.

surface feet per minute

sfm. A measurement of speed that is a direct function of the workpiece or grinding wheel diameter and its rate of rotation. Surface feet per minute measures the number of feet that a location on the periphery of a rotating component travels in one minute.

surface speed

The uniform rate at which the regulating wheel revolves against the workpiece during centerless grinding. Surface speed controls the work speed of the workpiece.

tangents

A line that is perpendicular to the radius and intersects a circle at one point only. Tangents between the workpiece and each wheel form the gamma angle during centerless grinding.

tapers

A gradual decrease in the width of an object. A taper is ground into a workpiece using endfeed grinding.

test bar

A cylindrical setup tool that has a diameter that is the same as or slightly smaller than the workpiece diameter and extends beyond the width of the regulating wheel on both sides. A test bar, or alignment bar, is used to find the proper clearance between the work guides and the workpiece.

throughfeed

The feeding of a workpiece past the grinding wheel in a straight line. Throughfeed grinding occurs in centerless grinding when the regulating wheel, tilted at the angle of inclination, moves the part along the work rest blade and across the grinding wheel periphery.

throughfeed grinding

A method of centerless grinding in which the regulating wheel moves the rotating workpiece axially along the work rest blade and past the grinding wheel in a straight line. In throughfeed grinding, the regulating wheel moves the part completely past the grinding wheel.

throughfeed rate

The rate at which the workpiece passes axially between the grinding and regulating wheels. Throughfeed rate is controlled by the regulating wheel.

wear-resistant

Able to withstand the mechanical and chemical phenomena that cause wear during an abrasive grinding process. Being wear resistant is an important property for a work rest blade.

wheel slide feed screw

A screw that can be adjusted to position the grinding wheel. The wheel slide feed screw moves the grinding wheel slide in 0.0001 in. (0.0025 mm) or 0.0000125 in. (0.000375 mm) increments.

whipping

The occasional unwanted vibration between components. Whipping, also called whirling, is often caused by kinks or bends in the part.

work center height

The linear measurement of the distance that the workpiece centerline lies above the plane drawn between the centerlines of the grinding wheel and regulating wheel. The work center height must remain above the wheel centerline to avoid lobing.

work guides

A centerless grinder component located at the beginning and end of the machine to position the workpiece as it enters and exits. Work guides, or work rest guides, are used for throughfeed centerless grinding.

work rest

A centerless grinder component that supports the workpiece as it is ground. The work rest is mounted on the lower slide and supports the work rest blade.

work rest blade

A device that supports cylindrical parts during centerless grinding. Work rest blades often have an edge that angles toward the regulating wheel.

work speed

The peripheral speed of the workpiece. Work speed is approximately equal to the surface speed of the regulating wheel.

workpiece

A part that is in the process of being manufactured. A workpiece may be a complete product by itself or one component of a product consisting of many parts.