Fault Finding and Correction Guide

Customer Support

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.
	Wide, regularly spaced marks	Pulley loose or out of balance	Eliminate looseness. Balance pulley.
	Long, regularly spaced marks	Wheel out of balance	Wheel face out of round.
	Long, regularly spaced marks	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.
	Irregular scratches	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.
	Grain marks	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.
	Fine spirals	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.
	Wide, regularly spaced marks	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.
	Long, regularly spaced marks	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.
	Irregular chatter marks	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.
		Dust settling on machine	Install dust collectors.
	Deep isolated scratches	Incorrect wheel dressing	Dress wheel face with sharp diamond dresser.
		Incorrect wheel dressing	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.
	Irregular marks of various lengths	Dirty coolant	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.
	Uneven traverse lines	Table traverse mechanism worn	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.
		Wheel specification unsuitable	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.
	Out-of-round work	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.
		Faulty machine or setting	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.
Burn	Discolored workpiece	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.
		Wheel specification unsuitable	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).
		Incorrect wheel dressing	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.
		Incorrect wheel dressing	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.
		Improper regulating wheel	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
	Out-of-round work	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.
Burn, cracks		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.
Radial break in 3 or more pieces	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.