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Dressing And Trueing

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Dressing And Trueing

Dressing And TrueingDressing
When the sharpness of grinding wheel becomes dull because of glazing and loading, dulled grains and chips are removed (crushed or fallen) with a proper dressing tool to make sharp cutting edges and simultaneously, make recesses for chips by properly extruding to grain cutting edges. Thus, these operations are for the dressing.

Trueing
When the grinding wheel is mounted to the grinding wheel spindle, the run-out on wheel operating surface is removed, the wheel during contour grinding is trued or worn grinding wheel is corrected. Thus, these operations are for the trueing.

Table of Dresser Uses by Grinding Tool

T: trueing; D: dressing; ◎: used; ○: can be used; △: is sometimes used

Dresser typeDiamond wheelCBN wheelConventional
wheel
Vitrified
Resinoid
Metal
Plated
Vitrified Resinoid Metal Plated
T D T D T D T D T D T D T D T D D
Single-point                            
Multi-point                          
Impregnated                      
Cap rotary                          
Rotary            
Vitrified diamond wheel                      
Resinoid diamond wheel                            
Metal diamond wheel                      
plated diamond wheel                          
Diamond roller                          
Diamond block                        
Wheel block grinder                  
Wheel brake control          
Wheel roller drive                  
Wheel stick push                    
Mild steel grinder                      
Metal crusher                          
Metal wire brush                              
Crushing roller                        
Abrasive lapping          
Abrasive jet                      
Abrasive sludge pouring                        
Wire electrode discharge                          
Electrolysis                              

Main dressing and sub-trueing tool

One diamond is mounted to the shank in various methods. Size is indicated at weight (carat … ct), the units of 1/4, 1/3, 1/2, 3/4, 1, 2, 2.5, 3ct, etc. are usually used (1ct = 0.2g).
There are diamond shapes such as normal type and pyramid, cone, wedge types reshaped for profile grinding.

Single-point
forming
diamond dresser
Single-point dressers

Normal type

Natural diamond is used by extruding the edge of rough stone as is. This type is used for general grinding.
Point dressers (pyramidal and conical)

Pyramid type (point dresser)

The rough diamond is formed to quadrangular pyramid. This type is for precision grinding to use the sharp edge.

Cone type (point dresser)

Rough diamond is formed to the cone type and its tip cutting edge is used for the precision thread grinding, gear grinding, etc.
Forming dressers

Wedge type (forming dresser)

One diamond polished to shape and sizes matched to used tool is embedded for precision form grinding.

 Reishauer dressers

The diamonds of Resihaur dressers are ground to be flat and parallel with the shank.
Resihauer dressers are used to shape wheels for gear grinders.
(Origin of name: these dressers are used with the grinding machines made by Reishauer AG.)

Multi-point
types


Multi-point diamond dresser

Two to tens of diamond are embedded in this dresser. It is called what piece what step by the number of diamonds on surface and the number of steps on layer. Since the diamonds of this dresser are hardly damaged, even operator who is not expert, it can be easily used.
Needle dresser

Blade type multi-point diamond dresser

Some diamonds are arranged in a line or layered. Two or more of diamonds are continually used so as to be contacted. This type is economical since it can be used to the end without correction. It is also used for form grinding.
Impregnated dressers

Impregnated diamond dresser

The diamond powers (#60 ~ #400) are sintered with high wear resistance metal. This dresser is used for the grinding wheel of precise grinding.
Grit dressers

Bond diamond dresser (grid dresser)

The infinitesimal grains (#16 ~ #40) of diamond are sintered with high wear resistance metal. This dresser is suitable to a large type grinding wheel like the centerless grinding wheel.

Detailed single point diamond dresser

Grinding performance is influenced by the conditions of dressing and trueing. If the rigidity of dresser is small and the dresser is incorrectly mounted, correct dressing is impossible. The diamond dresser is usually tilted to 15°of angle. When set less than this angle, the finished surface becomes wrong.

How to mount single point diamond dresser correctly

How to mount single point diamond dresser correctly How to mount single point diamond dresser correctly
The grinding wheel is mounted at 10 ~ 15°of angle for horizontal face of wheel. The grinding wheel is mounted at 10 ~15°of angle for circumference of wheel.

The effect that feed speed, cut depth and mounting angle of the dresser have on finished surface roughness is shown in the graph. As the mounting angle gets wider the finished surface roughness gets smoother.

Feedrate of dresser

As the feedrate increases, the cutting blade gap grows wider and the sharpness of the wheel increases but machining precision gets worse. Conversely, as speed decreases, machining precision improves but it becomes more prone to clogging and cutting ability decreases. One guide with the dresser feedrate is to go over every grain 2 to 3 times, which can be determined with the following equation.

Feed SpeedF = (d×N)/2.5
F: Dresser feedrate (mm/min)
d: Average grain diameter (mm)
N: Wheel rotation count (1/min)

Granularity F46 F54 F60 F80 F100 F120 F150
Average grain diameter 0.4 0.3 0.25 0.18 0.13 0.10 0.07

Depth of Cut and Total Depth of Cut

The effect of depth of cut on grinding performance is not large enough to impact the feed speed, but the fractured state of the grain can change, so it is related to finished surface roughness.
A small depth of cut with a radius of about 5 μm should be set for precision grinding due to the production of minute fractures in the grain.
For general grinding, the depth of cut is set to a radius of about 10 – 30 μm in order to break down the grain properly.
For rough grinding, a depth of cut radius can be set to about 40 μm, which partially breaks down the bond bridge, widening the grain spacing and greatly increasing the amount of material removed.

On the other hand, the total cut depth can change the wear and clogging of the grain. Performance cannot be improved or restored when the total depth of cut is not sufficient, and excess depth of cut can invite insufficient grain protrusion. For a general grain, one guide should be 10 – 30% of grain diameter, and it is recommended that you check whether the prescribed performance (finished surface roughness, dress gap, etc.) has been restored or improved.

How to select diamond size

The diamond size is determined by grain, grain size, grade, bond and sizes (diameter × thickness) and it is selected as follows.

Abrasive grain: C-system more than A-system is ……………….large.
Grain size: Rough grain more than fine grain is ……………….large.
Hardness: Hard diamond more than soft diamond is ……………….large.
Bond: Organic more than minerals is ……………….large.
Grinding wheel diameter: Large diameter is ……………….large.
Grinding wheel thickness: Large thickness is ……………….large.

Trouble by dressing failure and it’s troubleshooting

Problems that arise during dressing are directly connected to grinding problems. In order to get sufficient performance from wheels, dressing must be correctly carried out.
Items related to dressing that can be checked in order to prevent defects from arising during grinding are given below.

ConditionTroubleshooting
Irregular chatter • Use sharp diamond dresser.
• Replace tip-flatted dresser with new one.
• Check diamonds are securely held.
• Check dresser shank is not excessively protruded.
Scratch (Fine threading mark) • Check diamond is not broken.
• Reduce diamond feed.
• Mount diamond dresser downward 15°.
• Mount holder securely.
• Reduce depth of cut for dresser and feed dresser several times at infeed amount.
• Be sure to dress from grinding wheel edge.
• Feed dresser finally in reverse direction as grinding feed.
• Feed dresser uniformly.
• Round end faces of grinding wheel.
Feed mark • Reduce infeed amount and feed for dresser.
Irregular flaw • Use sharp diamond dresser.
• Brush grinding wheel after dressing.
Large consumption of wheel • Reduce depth of cut and increase feed.
Loading of grinding wheel • Use sharp diamond dresser.
• Increase dresser feed.
• Clean surface after dressing.
Glazing of grinding wheel • Increase dressing times with sharp diamond dresser.
• Increase infeed amount and feed of dresser.
Roundness failure of workpiece • Check wheel operating surface is not loaded or glazed.
• Match dressing position and grinding position.
Workpiece tapered • Approach diamond dresser to grinding position.
Burn marks, braking • Increase dresser feed and dressing times.
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