Cylindrical Grinders Unit 83

Objectives Set up and grind work on a cylindrical grinder Internal-grind on a universal cylindrical grinder Identify and state the principles of three methods of centerless grinding

Cylindrical Grinder Grinds accurately to size and high surface finish the diameter of a workpiece Two types of machines Center type Plain – Generally manufacturing type of machine Universal – More versatile since wheelhead and headstock may swivel Centerless type

Universal Cylindrical Grinder Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Parts of the Universal Cylindrical Grinder Base Heavy cast-iron construction for rigidity Top of base machined to form ways for table Wheelhead Mounted on cross-slide at back of machine Mounted on ways right angle to table way May be swiveled to permit grinding of steep tapers by plunge grinding

Parts of the Universal Cylindrical Grinder Table Mounted on ways, driven back and forth by hydraulic or mechanical means Lower table rest on the ways Upper table may be swiveled Headstock and footstock used to support work held between centers Trip dogs Control reversal of table

Parts of the Universal Cylindrical Grinder Headstock Mounted on left end of table Contains motor for rotating work Dead center mounted in headstock spindle and used to overcome any spindle inaccuracies Two dead centers rotate work mounted between centers by means of dog and driveplate Footstock Supports right end of work (adjustable)

Parts of the Universal Cylindrical Grinder Backrest (steadyrest) Provides support for long, slender work and prevents it from springing May be positioned anywhere along table length Center rest Resembles lathe steadyrest Mounted at any point on table Used to support right end of work when grinding confined to end of workpiece

Parts of the Universal Cylindrical Grinder Internal grinding attachment Mounted on wheelhead for internal grinding Usually driven by separate motor Diamond wheel dresser Clamped to table to dress grinding wheel Coolant system Provide dust control, temperature control and better surface finish on workpiece

Procedure To True and Dress the Wheel Start grinding wheel to allow spindle bearings to warm up Mount proper diamond in holder and clamp it to table Diamond should be mounted at angle of 10º to 15º to wheelface and held on centerline of wheel Adjust wheel until diamond almost touches high point of wheel

Turn on coolant if it is to be used for grinding operation Feed wheel into diamond about .001 in. per pass Move it back and forth across wheelface at medium rate until wheelface has been completely dressed Finish-dress wheel by using infeed of .0005 in. and slow traverse feed

Procedure to Parallel-Grind an Outside Diameter Lubricate machine as required Start the grinding wheel to warm up spindle bearings True and dress grinding wheel, if required, and then shut off spindle Clean machine centers and center holes of workpiece

Align headstock and footstock centers with test bar and indicator Lubricate center holes with suitable lubricant Set headstock and footstock for proper length of work so center of work will be over center of table Mount work between centers with dog mounted loosely on left end of work Tighten dog on end of work and engage driveplate pin in fork of dog

Adjust table dogs so wheel will overrun each end of work by about one-third of the width of the wheelface Set grinder to proper speed for wheel being used Set work speed for diameter and type of material being ground Set headstock spindle to revolve work in opposite direction to that of grinding wheel

If machine equipped, set automatic infeed for each table reversal Set dwell time which permits wheel to clear itself at each end of stroke Select and set desired table traverse or speed Table move one-half or two-thirds of wheel width per revolution of work Start table and move wheel up to workpiece until it just sparks

Engage wheelfeed clutch lever and grind until work cleaned up Check work for taper and adjust if necessary Determine amount of material to be removed and set feed index for this amount Infeed of wheel will stop automatically when work at proper diameter Stop machine with wheel clear of work and measure size of workpiece

To Grind a Tapered Workpiece Work held between centers Ground in same manner as parallel work Exception: table swiveled to half the included angle of the taper Taper should be checked for accuracy after workpiece cleaned up Short, steep tapers ground by swiveling wheelhead to desired angle and plunge-grinding tapered surface with face of wheel

Plunge Grinding Feeding wheel into revolving work with table remaining stationary Grinding wheel fed automatically to setting on feed index Dwells for suitable time to permit "spark out" and retracts automatically Length of surface to be ground must be no longer than width of grinding wheel face

Internal Grinders Designed for accurate finishing of holes in workpiece by grinding wheel Originally designed for hardened workpieces Now used for finishing holes in soft material Wheel fed into work automatically until hole reaches required diameter Wheel withdrawn and automatically dressed

Internal Grinding on a Universal Cylindrical Grinder Used in toolrooms for this purpose Attachment mounted on wheelhead column Swung into place when required Outside and inside diameters of workpiece may be finished in one setup Grade of wheel will depend on type of work and rigidity of machine

Wheels Used for Internal Grinding Generally softer than those for external grinding Larger area of contact between wheel and workpiece Requires less pressure to cut than hard wheel Reduced spindle pressure and spring

Procedure To Grind Parallel Internal Diameter on Universal Cylindrical Grinder Mount workpiece in universal chuck, collet chuck, or on faceplate Swing internal grinding attachment into place and mount proper spindle in quill Mount proper grinding wheel for job Adjust spindle height until center is in line with center axis of hole in workpiece

True and dress grinding wheel Set wheel speed to 5000 to 6500 sf/min Set work speed to 150 to 200 sf/min Adjust table dogs so only one-third of wheel width overlaps ends of work at each end of stroke Blind holes – dog set to reverse table just as wheel clears undercut at bottom of hole Start work and grinding wheel

Touch grinding wheel to diameter of hole Turn on coolant Grind until hole just cleans up, feeding wheel in no more than .002 in. per table reversal Check hole size and set automatic feed to disengage when work roughed to within .001 in. of size Reset automatic infeed to .0002 in. per table reversal

Finish-grind work and let wheel spark out Move table longitudinally and withdraw wheel and spindle from workpiece Check hole diameter and finish-grind if necessary

Procedure To Grind a Tapered Hole Same procedures and precautions should be followed as for grinding parallel holes Exception: Workhead must be set to one-half included angle of taper Very important that centerlines of grinding wheel and hole be set at same height

Centerless Grinders Work not supported on centers but by work rest blade, a regulating wheel, and a grinding wheel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

How Centerless Grinders Work Work supported on work rest blade equipped with suitable guides Rotation of grinding wheel forces work onto rest blade against regulating wheel Regulating wheel controls speed of work and longitudinal feed movement Set at slight angle (angle controls rate of feed) Centers fixed – diameter of work controlled by distance between wheels and height of work rest blade

Methods of Centerless Grinding Three methods Thru-feed Infeed Endfeed

Thru-Feed Centerless Grinding Consists of feeding work between grinding and regulating wheels Work fed by regulating wheel past grinding wheel Speed of feeding work controlled by speed and angle of regulating wheel Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Infeed Centerless Grinding Form of plunge grinding Used when work being ground has shoulder or head Several diameters of workpiece may be finished simultaneously Work rest blade and regulating wheel clamped in fixed relation to each other Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Endfeed Centerless Grinding Used for grinding tapered work Grinding wheel, regulating wheel, and work rest remain in fixed position Work fed in from front up to fixed stop Grinding wheel and regulating wheel often dressed to required taper Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Advantages of Centerless Grinding No limit to length of work being ground No axial thrust on workpiece Permits grinding of long workpieces that would be distorted by other methods Less stock required on workpiece for truing purposes Less wheel wear and less grinding time required because there is less stock to be removed

Check textbook for full tables that list the faults that might occur with the probable causes and a suggested remedy. Table 83.1   Cylindrical grinding faults, causes, and remedies Table 83.2   Internal grinding problems, causes, and remedies