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Relationship between machanical conditions and grinding results

Management of grinding operation problems
  1. Effective problem management
  2. Grinding operation problems and management
Effective problem management
Since specific technologies are noted in sention.2 regarding grinding wheel problem management, in this section general examples of problem management are given.

First, a concreate grasp of the facts is nessary. For instance, the claim that the grinding wheel itself is hard is vague and may easily be mistaken. As well, making judgments based simply upon numerical figures can also cause mistakes.

So far dressing has been made every 20 units, but with the 15th unit, a shear is produced at the edge and the product becomes inferior, the lift span of one wheel declines from 20 to 15 days.

So far dressing has been made every 20 units but with the 15th unit, loading curred and the wheel life span for one unit goes from 20 to 15 days.

In such cases, if we think simply of dressing interval and wheel life span, it seems that the treatment solving the problem is identical. However, treatment for the shear at the edge is completely different from that for loading. The treatment should be opposite because the grinding wheel is soft for case and hard for case.

Second, think sufficiently about mutual relations. For instance, if it is desired to improve surface roughness, there are methods such as,

  • making the grain size finer
  • if using a vitrified grinding wheel, changing to a resinoid grinding wheel
  • improving mechanical precision
  • increasing zero-cutting (spark-out) frequence
  • changing grinding fluid

However, there are also disadvantages for each item:

  • grinding ability is generally reduced
  • peripheral wheel speed and grinding fluid price are also problems
  • huge expenses are required
  • depending on the grinding machine type it is impossible
  • depending upon type of machine or wheel it is impossible

In such cases there is a strong tendency to change only the grain size as an acceptable method to prevent efficiency from declining. However, if mutual relations and actual on-site conditions are not carefully considered, it will take many months to solve the problem after conduction all the above methods with successive failures. There was the case when the problem was finally solved by making the dressing feed finer. In logical terms this was the most correct method.

We must think of the grinding process in terms of 5 related items:

  • Machine
  • Wheel
  • Workpiece
  • Grinding fluid
  • Operation method

It is important not to focus too teavily on any one of these. Since the process of solving major problems becomes a valuable bit of technological data, it is neccessary that it be preserved. As for usual data, this should be organized in control charts or graphs. The data for each wheel should be filled in on the back of the inspection card and such feedback to the wheel macturer can prove to be extremely efficient.


Grinding operation problems and management

Machine vibrations, chatter and scratch to the finished surface

In the case of chatter
Condition Cause Management
Wave appears in the same internal Machine vibration 1.Check foundation and positioning method
2.Replace or adjust belt and gears
3.Check spindle and motor balance
4.Recheck moving parts
Wheel unbalance 1.Retake wheel balance
2.Retake balance also after resurfacing
3.Stop wheel rotation after grinding fluid pouring is finished
Wheel isn't round 1.Resurface wheel before and after taking balance
Wheel is hard 1.Use a soft grade wheel
2.Use a rough grain size wheel
3.Reduce peripheral wheel speed
4.Reduce depth of cut
Narrow, deep and regular chatter Wheel is rough 1.Use fine grain size wheel
Irregular chatter Unacceptable placement of workpiece 1.Eliminate looseness in placement
2.Check center rest and revise if necessary
3.Lubricate correctly
Workpiece unbalance 1.Take balance of workpiece
2.Use large scale grinding machine
Unacceptable 1.Use a sharp diamond
2.Replace diamond with worn down adges
3.Make sure there is no looseness in diamond holder
4.Don't protrude dresser for too long
Both regular and irregular chatter appear Thrust feed looseness 1.Conduct thrust inspection
3.Conduct feed equipment inspection
Chatter appears in a wide range for a long time Unbalanced movement and vibration of wheel axis 1.Check to see if wheel axis is round
2.Check for curves in wheel axis
Even spread and short with contact chatter Bearing looseness 1.Undertake wheel bearing fitting
2.Revise thrust
3.Reduce peripheral wheel speed
Wide and various deep irregular streaks Wheel is soft 1.Use a hard grade wheel
Wide distribution of dots Wheel glazing 1.Take wheel balance and conduct dressing
2.Remove adhering fluid from wheel surface

In the case of search and spiral mark
Condition Cause Management
Fine spiral streaks (Scrarches) Unacceptable dressing 1.Replace broken diamond
2.Slow down dressing feed
3.For installing, make a bottom placement of 15 degrees and a side placement of 30 degrees
4.Confirm the holder placement
5.Make shallow dresser depth of cut
6.Make sure holder does not touch wheel
7.Begin dressing from end face of wheel, not from the surface mid-point
8.Make sure the final dressing feed is in the opposite direction from the grinding feed
9.Make sure the dresser feed is even
10.Round the end face of the wheel
Unacceptable grinding operations 1.Make sure wheel surface and workpiece are parallel and avoide uneven placement of one side of workpiece to wheel surface
2.Reduce wheel pressure
3.Use a fixed rest
4.Reduce the wheel feed
Spiral stripes (Spiral marks) Contact condition of wheel end face 1.Round the wheel end face
Grain size difference between rough finished wheel and finished wheel is too great 1.For rough finished wheels, use wheel with finer grain size
2.For finished wheel, use rougher size grain wheel, reduce the depth of cut and feed and finish untill there are no more sparks
Dressing is rough 1.Make dressing depth of cut shallow and slow down the feed
Finished grinding is incorrect 1.Firstly, speed up the feed and remove the strak from the rough finish
2.Finally, slow down the feed and finish with an empty depth of cut
Inacceptable alignment 1.Check the alignment of the workpiece center
2.Check the alignment of the wheel axis with workpiece
Isolated deep scratch Unacceptable dressing 1.Use sharp diamond
2.Brush wheel surface after dressing (Abristle brush is acceptable)
Entry of rough grain or foreign substance 1.Remove with dressing
2.Replace wheel if amount is large
Resinoid wheel deterioration 1.Avoid chemical solution type (JIS W-3) and use soluble type (JIS W-2) instead
2.Limit level of alkaline to Ph 9
3.Protect against summer rise in grinding fluid temperature
Abrasive grain accidental fallout 1.Use a wheel with a hard grade
2.Use abrasive grain with rise in grinding fluid temperature
Various lengths and widths with irregular scratches Dirty grinding fluid 1.Keep tank clean on regular basis
2.Check function of filtration equipment
3.Keep inside of safety cover clean
Dust and debris 1.Inspect the dust collection function, especially the suction opening
2.Undertake cleaning of the operations area
Checkered pattern Unacceptable grinding operation 1.Do not press wheel too far into workpiece
2.Perform operation using wheel in soft gentle way
3.Pour grinding fluid evenly and sufficiently

Unsuitable grade of grinding wheel, loading and glazing
Condition Cause Management
Poor sharpness of cut
3.Burn mark of processing surface
4.Chatter occurring at the same time
Wheel grade is hard 1.Increase workpiece speed, wheel feed and wheel pressure
2.Reduce number of wheel rotations, wheel diameter and thickness
3.Apply dression from time to time using a sharp dresser
4.Don't stop at the stopping point of the coming and going table
5.Carefully select grinding fluid (Straight oil type JIS W3, W2 in the case of water soluble type) Increase the magnification of grinding fluid
6.Use a coarse grain size or a soft grade wheel

Wheel over consumption Non-grinding tapered workpiece Scratch on wheel shedding Wheel grade is soft 1.Reduce workpiece speed, wheel feed and wheel pressure
2.Increase number of wheel rotations, wheel diameter and wheel thickness
3.Make dressing depth of cut shallow, increase feed
4.Dont' release wheel from workpiece on both sides of table
5.Make frinding fluid magnification thinner
Wheel loading Wheel is improper 1.Use coarse grain size wheel
2.Use soft grade wheel
3.Use coarse structure wheel
Dressing is improper 1.Use a sharper diamond
2.speed up the dressing feed
3.Clean wheel surface after dressing
Grinding fluid is improper 1.Use fluid with good cleanliness (JIS W3, W2)
2.Apply fluid in balanced and generous way
3.At time of central lubrication, use caution for grinding fluid cleaning
Operation is improper 1.Perform operations using wheel in a soft, gentle way (Refer to poor sharpness of cut listing)
Wheel glazing Wheel is improper 1.Is the choice of abrasive grain for the workpiece material proper?
2.Use a wheel which has coarse grain size, soft grade and coarse structure
Dressing is improper 1.Dress normally with sharp dresser
2.Speed up the dresser feed
3.Deepen the dresser depth of cut
Grinding fluid is improper 1.Choose a fluid with good lubricating alility (Straight oil type, Water soluble type W2)
2.Apply fluid in a balanced and generous amount
3.Devise a method for applying grinding fluid
Operation is improper 1.Increase depth of cut
2.Perform operations using wheel in soft, gentle way (Refer to poor sharpness of cut listing)

Workpiece precision, burn marks and cracks
Condition Cause Management
Imperfect roundness Imperfect alignment of center rest 1.Open center hole accurately
2.Grind and lap the center hole, or remove the dust
3.Regrind the center point
4.Lubricate the center hole and point sufficiently
5.Eliminate looseness from center rest
6.When centerless grinding, adjust rest height to approximately 10mm.
Imperfect dressing 1.Line up the machine's various conditions with the grinding position and dressing position
Unbalance in workpiece 1.Use a balance weight
Improper operation 1.For longitudinal feed, don't release wheel from workpiece (if not doing so, the end of the workpiece will be tapered)
2.Reduce pressure on depth of cut
3.Use a harder wheel
4.Use a rest for a long or thin workpiece
Imperfect cylindricity (will be tapered) Improper wheel 1.Use a harder wheel
2.For pluge cutting, make wheel width larger than workpiece width
Dressing imperfection 1.Bring diamond adge into contact with grinding point
Improper operation 1.Rewview placement of the rest
2.Is the table feed smooth?
3.Leave at least one third of wheel width by horizontal feed
Workpiece expansion 1.Apply a great deal of grinding fluid
2.Use caution in lubrication method
3.Redice depth of cut, quicken the feed
Residual stock removal 1.Use a harder wheel
2.Review pre-finishing and replace wheel after a certain interval
3.Is the zero cutting time proper?
Grinding burn marks and grinding cracks Improper wheel 1.Use a hard grade, coarse structure wheel
2.Perform operations using wheel in soft, gentle way (Refer to poor sharpness of cut listing)
3.Make fine dressing, apply occasionally
Improper grinding fluid 1.Apply grinding fluid in generous, uniform way
2.Devise lubricating method so that grinding point is lubricated (Central lubrication etc.)
3.Use fluid with good lubricating ability (Straight oil type is recommended)
4.If water soluble type, use a strong type such as JIS W2 after thickening
Improper operation 1.Reduce depth of cut
2.Speed up the feed, don't grind in one place
3.Don't stop wheel while in contact with workpiece
Improper heat treatment of workpiece 1.Is the tempering temperature too low?
2.Is there an unstable structure remaining at the workpiece?
Warp of thin workpiece Improper operation 1.Reduce magnetic force of magnet chuck
2.Insert an iron plate of proper thickness betwee chuck and workpiece
Improper grinding fluid (Refer to grinding burn marks and cracks listing)
Improper wheel Same as above