KGW HOMECustomer SupportGrinding Wheel Use and Precautions Fault Finding and Correction Guide to Correct Them

Customer Support

Fault Finding and Correction Guide

Common grinding faults

Problem Possible Causes Suggested Correction
Chatter
vibration
Regularly spaced marks
Vibration Rebalance motor and wheel.
Wide, regularly spaced marks Vibration from belt Repalce belt.
Pulley loose or out of balance
Eliminate looseness.
Balance pulley.
Long, regularly spaced marks Wheel out of balance Wheel face out of round.
Wheel face out of round
True wheel before balancing.
Short, close, evenly spaced marks
Spindle bearings loose Adjust spindle bearings.
Warm up gringing machine to reach appropriate temperature.
Check thrust bearing.
Slightly longer and more widely
spaced marks
Wheel spindle run-out or out
of round
Replace wheel spindle.
Long, widely spaced marks Drive gear backlash Replace gears.
Introduce V belt drive.
Check lubricated condition.
Regular or irregular marks
Faulty thrust bearing Replace thrust bearing.
Narrow, regularly spaced marks
Spindle pulley loose Tighten spindle pulley.
Longish, widely spaced discolored
marks, distributed evenly
Glazed or loaded wheel Use coarser grit, softer grade or more open structure wheel.
Chatter marks Incorrect wheel dressing Redress wheel face with sharp diamond dresser.
Mount diamond dresser rigidly in holder.
Irregular marks Center holes out of round or not
in line
Steady rests improperly adjusted
Check work center holes for roundness ad alignment.
Check workpiece for fit to centers.
Check lubricated condition between work center holes and centers.
Adjust steady rests.
Marks synchronized with floor
vibration
Vibration from floor For large machines, build additional foundation separated from floor.
For normal machines, try adjusting anchor bolts.
Try changing machine location.
Mount machine on some vibration insulating material.
Mottle marks Glazed wheel Balance and redress wheel.
Remove grease or oil spots from wheel face.
Deep, narrow regular marks Wheel too coarse Use finer grit wheel.
Problem Possible Causes Suggested Correction
Scratching
Feed marks
Deep isolated scratches
Shedding Use harder acting wheels.
Use more friable abrasive grains.
Incorrect dressing Redress wheel face with sharp diamond dresser.
After dressing, clean wheel surface with stiff-bristled brush.
Contamination by coarse grits or
foreign matters
Dress or replace wheel.
Flanges loose Insert blotters between wheel surface and flanges and tighten
screws evenly.
Organic wheel deteriorated Do not use solution-type coolant.
Prevent rise in coolant temperature with cooling system
during summer.
Limit maximum pH (alkalinity) to 9.
Irregular scratches Dirty coolant Clean and check coolant circulating system, in particular, filter,
tank, and inside guard.
Dust or othe particles Check dust collector for proper functioning and improve work
enviornment.
Draughtsboard pattern Faulty grinding operation Do not excessively force wheel onto workpiece.
Make wheel act softer.
Supply large and equal volume of coolant to grinding point.
Grain marks Wheel too soft
Wheel too coarse
Use finer grit or harder grade wheel.
Incorrect wheel dressing Dress wheel with lighter cuts and slow diamond traverse rate.
Fine spirals Incorrect wheel dressing Replace diamond dresser.
Reduce traverse feed at even rate and take lighter dressing cuts.
Mount diamond dresser rigidly at angle of 15 degrees against
wheel rotaion.
Make final dressing in opposite direction to initial runs.
Round off wheel edges.
Faulty grinding operation Prevent wheel edge from digging in workpiece.
Grind workpiece under light load which provides low grinding force,
and use additional steady rests so that it cannot be inclined by
grinding force.
Reduce table speed or change some speed per pass.
Spiral feed marks Contact with wheel edge Round off wheel edges.
Wrong grit size Use finer grit for rough finishing and relatively-coarse grit for finishing.
Reduce wheel infeed rate and traverse rate gradually to allow wheel
to completely spark out.
Incorrect wheel dressing Take lighter dressing cuts and reduce diamond traverse rate.
Head and tailstock out of alignment Check head and tailstock, and tableways.
Problem Possible Causes Suggested Correction
Loading
Glazing
Shedding
Large wheel wear
Grinding marks on workpiece
Workpiece tapered
Shedding
Wheel too soft

Reduce wrok speed, wheel traverse rate and wheel infeed rate.
Increase wheel speed, wheel diameter, and wheel thickness.
Take lighter dressing cuts and reduce diamond traverse rate.

Poor cutting ability
Wheel glazing
Wheel loading
Burned work
Chatter marks
Wheel too hard Increase work speed, wheel traverse rate and wheel infeed rate.
Reduce wheel speed, wheel diameter, and wheel thickness.
Redress wheel face frequently with sharp diamond dresser.
Use coarse grit, or softer grade wheel.
Loading
Wheel specification unsitable Use coarser grit, softer grade, or more open structure wheel.
Incorrect wheel dressing Use sharp diamond dresser.
Increase diamond traverse rate and then clean wheel surface.
Poor coolant quality Change coolant or use high detergent type.
Faulty grinding operation Grind under conditions which provide softer wheel acts.
Glazing
Wheel specification unsuitable Use coarser grit, softer grade, or more open structure wheel.
Use more friable abrasive grains.
Incorrect wheel dressing
Use sharp diamond dresser.
Increase diamond traverse rate.
Take heavier dressing cuts.
Poor quality/quantity coolant Increase lubricity of coolant.
In addition to improving coolant supply method, supply
large and equal volume of coolant to grinding point.
Faulty grinding operation Grind under conditions which provide softer wheel acts.
Problem Possible Causes Suggested Correction
Burn, crack,
and workpiece
inaccuracy
Burnt and cracked work
Wheel specification
unsitable
Use softer grade, or more open structure wheel.
Dress more frequently.
Poor coolant quality,
quantity and distribution
Increase lubricity of coolant.
(Oil or water-soluble coolant is better for use.)
Supply large and equal volume of coolant to grinding point.
Improve coolant supply method and direct coolant effectively
at grinding points. (Ex. Installtion of high-pressure coolant system.)
Faulty grinding operation Reduce wheel infeed rate and increase wheel traverse rate.
Inadequate heat treatment
of workpiece
Increase tempering temperature and remove any
remaining unstable structure from workpiece.
Out-of-round work Incorrect work centers
Work not high eoungh above
center(centerless grinding)
Drill work center holes correctly.
Regrind and lap work center holes.
Lubricate centers and work center holes sufficiently.
Readjust work blade. (Centerless grinding)
Poor wheel dressing Adjust dressing tool so that the circumference of
the wheel touches the circumference of the work
Work out of balance Rebalance workpiece.
Faulty grinding operation Do not allow wheel to separate from work edge.
Reduce wheel infeed rate.
Reduce wheel speed and wheel diameter.
Wheel specification unsuitable Use softer grade wheel.
Out of cylindricity Wheel specification unsuitable For plunge grinding, ensure that wheel width is larger than work width.
Use harder grade wheel.
Incorrect wheel dressing Adjust dressing tool so that the circumference of
the wheel touches the circumference of the work
Faulty grinding operation Check steady rest position.
Feed table more smoothly.
Do not allow wheel to separate from work on both edges.
Work thermally-expanded Supply plant of coolant.
Re-examine coolant supply method.
(Ex. Installation of high-pressure coolant system.)
Reduce wheel infeed rate and increase wheel traverse rate.
Workpiece not flat or
parellel (thin workpiece)
Faulty grinding operation Insert suitably-thick metal lat between magnetic
chucks and workpiece to reduce magnetic force of chuck.
Wheel specification unsuitale Use softer grade, or coarser grit wheel.
Dress more frequently.
Poor coolant quality,
quantity, and distribution
Increase lubricity of coolant.
(Oil or water-soluble coolant is better for use.)
Supply large and equal volume of coolant to grinding point.
Improve coolant supply method and direct coolant effectively
at grinding points. (Ex. Installation of high-pressure coolant system.)

Listed by Grinding Operation

(1) Cylindrical grinding

Problem Possible Cause Suggested Correction
Chatter vibration Chatter marks Incorrect wheel dressing Redress wheel face with sharp diamond dresser.
Mount diamond dresser rigidly in holder.
Short, close,
evenly spaced marks
Spindle bearings loose Reduce wheel speed.
Re-adjust and tight spindle bearings.
Give sufficient time for spindle bearings to warm up.
(Warm up grinding machine to stablize bearing temperature.)
Tighten thrust bearing.
Slightly longer and more
widely spaced marks
Wheel spindle run-out or out of
round
Replace spindle if it is twisted or warped, or out of round.
Regularly spaced marks Vibration Rebalance wheel.
Rebalance motor and wheel spindle.
Check fit between flanges and wheel spindle.
Short, regularly spaced
marks
Spindle pulley loose Tighten spindle pulley.
Wide, regularly spaced
marks
Vibration from flat belt Flat belts to have a uniform thickness and width.
All sections to have same pliability.
Pulley loose or out of balance Rebush or lap to suite spindle.
Balance carefully.
Regular, widely spaced
disclosed chatter marks
Wheel specification unsuitable Use coarser grit, softer grade, or more open structure wheel.
(More likely to be caused by glazed or loaded wheel.)
Long, regularly spaced
marks
Wheel out of balance True wheel before rebalancing.
Rotate wheel to spin out excess coolant.
Wheel face out of round True wheel before and after balancing.
True wheel perimeter and sides.
Long, widely spaced
chatter marks
Drive gear backlash Replace old and worn-out gear.
Introduce V-belt drive.
Check lubricated condition.
Regular or irregular
marks
Faulty thrust bearing Replace thrust bearing.
Even and regularly or
iregularly space marks
Belt joint (belt lacing) Use endless belt.
Irregular chatter marks Center holes out of round or not
in line
Check workpiece for fit to centers.
Lubricated centers and work center holes.
Rests improperly adjusted Adjust rests to fit to workpiece.
Problem Possible Causes Suggested Correction
Scratching Deep, narrow, regular
scratches
Wheel specification unsuitable Use finer grit wheel.
Wide, irregular scratches Wheel specification unsuitable Use harder grade wheel.
Mottle marks Faulty wheel face Balance and redress wheel. (Wheel glazing)
Irregular marks Belt fluttering Replace belt.
Dust settling on machine Keep air and shop clean.
Install dust collectors.
Deep isolated scratches Incorrect wheel dressing Dress wheel face with sharp diamond dresser.
After dressing, flush wheel face with coolant to clean.
Chemical action of cutting fluid If too strong alkaline coolant was used for organic bond, reduce soda content,
or change coolant.
Deep irregular scratches Flanges loose Re-tighten flanges.
Irregular marks of various
lengths
Dirty coolant Provide efficient filter.
Clean out tank more frequently.
Grain marks Wheel specification unsuitable Use finer grit or harder grade wheel.
Incorrect wheel dressing Dress wheel with ligher cuts and slow diamond traverse rate.
Incorrect grinding conditions Commence grinding using high work speed and wheel traverse rate to remove
previous wheel maks, finish with high work speed and slow traverse, and allow
wheel to completely spark out.
Spirals Fine spirals Incorrect wheel dressing Replace diamond dresser.
Dress wheel with lighter cuts and slow diamond traverse rate.
Mount diamond dresser rigidly in holder.
Make final dressing in opposite direction of initial runs.
Set diamond dresser downwards at angle of 15 degrees against wheel rotation.
Round off both wheel edges.
Faulty grinding operation Avoid having only one of wheel edges in contact.
Reduce wheel infeed rate.
Reduce wheel traverse rate per revolution of workpiece.
Arrange additional steady rests.
Uneven traverse lines Table traverse mechanism worn Eliminate looseness.
Replace all worn parts.
Spiral pattern on
workpiece whose lead
corresponds to traverse
Run-out Check centers for run-out.
Incorrect wheel dressing Mount diamond dresser tool to ensure that the point of diamond contact is that of
wheel contact on the workpiece.
Set diamond dersser download at angle of 15 degrees against wheel rotaion.
Round off both edges of wheel.
Problem Possible Causes Suggested Correction
Improper wheel grade Poor cutting ability
Wheel glazing
Wheel loading
Burned work
Chattering marks
Grade too hard Increase work speed and wheel traverse rate.
Increase wheel infeed rate.
Reduce wheel speed, outside diameter, and thickness.
Redress wheel face with sharp diamond dresser.
Use softer grade and / or coarser grit wheel.
Grindig marks on workpiece
Large wheel wear
Workpiece tapered
Grade too soft Reduce work speed and wheel traverse rate.
Reduce wheel infeed rate.
Increase wheel speed, outside diameter, and thickness.
Take lighter dressing cuts and reduce diamond traverse rate.
Do not allow wheel to separate from workpiece when table reciprocates.
Wheel loading Metal rigidly fixed on the
abrasive particles or lodged
in wheel pores
Wheel specification unsuitable Use coarser grit and/or more open structure wheel.
Use more friable abrasives.
Incorrect wheel dressing Dress wheel face with sharp diamond dresser.
Increase diamond traverse rate.
After dressing, flush wheel face with coolant to clean.
Poor coolant quality/quantity Supply plenty of cleaner coolant.
Faulty grinding operation Reduce work speed and wheel traverse rate.
Increase wheel speed, outsdie diameter, and thickness.
Supply plenty of coolant.
Wheel glazing Shiny appearance Wheel specification unsuitable Use softer grade and/or coarser grit wheel. Use more friable abrasives.
Incorrect wheel dressing Dress wheel face with sharp diamond dresser.
Increase diamond traverse rate.
Take heavier dressing cuts.
Incorrect quality coolant Reduce oil level - increase amount of coolant.
Faulty grinding operation Increase work speed and wheel traverse rate.
Reduce wheel speed, outside diameter, and thickness.
Increase wheel infeed rate.
Workpiece
inaccuracy
Out-of-round work Uneven pressure on driving dog Provide cushion between drive pin and driving dog.
See Causes and Suggested Correction for out-of-round work listed in Common Grinding Faults.
Out of cylindricity Faulty machine or setting Repair or replace worn parts.
Adjust both head and tailstock.
See Causes and Suggested Correction for out of cylindricity listed in Common Grinding Faults.
Burn Discolored workpiece Faulty machine or setting Adjust drive to avoid belt slippage.
See Causes and Suggested Correction for burnt and cracked work listed in Common Grinding Faults.

(2) Centerless grinding

Problem Possible Causes Suggested Correction
Chatter vibration Chatter marks Wheel specification unsuitable Use coarser grit or softer grade wheel.
Balance wheel.
Faulty grinding operation Reduce wheel infeed rate or workpiece through feed.
Incorrect wheel dressing Increase diamond traverse rate.
Faulty machine or setting Adjust spindle bearings, drives and other parts to eliminate looseness.
Lower wrok blade in relation to centerlines of two wheels.
Reduce blade grade. (An angle of approximately 30 degrees is good for general run
of work.)
Scratching
Feed marks
General lines/scratches Faulty machine or setting Grind work blade to eliminate dirt (chips and abrasives) and wear from it.
Wheel specification unsuitable Use harder grade wheel.
Dirty coolant Use clean coolant with greater lubricity.
Spirals with irregular
brightness
Faulty machine or setting Remove dirt or oil from work blade.
Incorrect wheel dressing Dress regulating wheel at the same angle as dressing grinding wheel
(in order to prevent bent caused by uneven grinding force).
Dress wheel to ensure that it has slight gradient upward to exit side.
Spirals Incorrect wheel dressing Dress wheel so it stops grinding 1/2 from exit edge.
Round off both edges of wheel.
Guides improperly adjusted Set guides parallel to wheel face by using lining bar of approximately equal diameter
to workpiece.
Workpiece
inaccuracy
Out-of-round work Wheel specification unsuitable Use softer grade wheel.
Balance and rederss wheel.
Redress regulating wheel as well.
Faulty grinding operation Make first cut light at high traverse rate to attain maximum straight effect.
Then use heavier cuts and finish with a light cut.
Poor quality/quantity coolant Supply plenty of clean coolant.
Incorrect workpiece center height Isodiametric shape (triangular or pentagon): Raise work center in relation to
wheel centerlines.
Polygonal (flower-petal) shape: Lower work center in relation to wheel centerlines.
Out of cylindricity Improper regulating wheel Concave workpiece: Increase angle of regulating wheel housing.
Barrel-shape workpiece: Decrease angle of regulating wheel housing.
Guides improperly adjusted Set entrance and exit guides parallel to wheel face.

(3) Internal grinding

Problem Possible Causes Suggested Correction
Workpiece
inaccuracy
Out-of-round work Faulty grinding operation Adjust work chuck
Incorrect wheel dressing Redress wheel face with sharp diamond dresser.
Out of cylindricity Wheel specification unsuitable Increase quill rigidity (by changing quill material for example.)
If it is caused by shedding, use harder grade wheel. If wheel acts too hard, use softer grade
wheel.
Faulty grinding operation Increase wheel width to size larger than workpiece width so that wheel edges on both sides
will not affect grinding.
Adjust wheel head angle and infeed rate.
Incorrect wheel dressing Redress wheel face with sharp diamond dresser.
Burn, cracks   Faulty grinding operation Increase work speed.
See Causes and Suggested Correction for burnt and cracked work listed in Common Grinding Faults.

Wheel breakage

Problem Possible Causes Suggested Correction
General breakage Incorrect wheel mounting on flanges Wheels to be good sliding fit on wheel spindle when mounted onto flanges.
(If too tight to slide on, wheel will be broken within 3 minutes of starting operation.)
Radial break in 3 or more pieces Incorrect grinding work
Faulty grinding operation
Do not use wheel at speeds exceeding maximum operating
speed marked on wheel or inspection sheet.
Prevent overheating caused by excessive infeed.
Prevent overheating caused by insufficient coolant.
Perform ring test on wheel before mounting wheel onto flanges.
Incorrect wheel mounting on flanges Do not tighten wheel with uneven pressure.
Flanges and wheel to be free from foreign particles in between.
Be sure to use blotters.
Radial break in 2 or more pieces Faulty grinding operation Avoid excessive force on wheel sides if wheel is allowed to grind on sides.