1. MACH 122: Abrasive Machining
Truing & Dressing
MACH 122: Abrasive Machining

2. Introduction TRUING, BALANCING & DRESSING tab
A grinding wheel must run true with every point on its cutting surface concentric with the machine spindle.
As the wheel becomes loaded with workpiece material, it must be dressed to restore sharpness.
It must also run in balance because of its great speed.
Truing, dressing, and balancing are important parts of grinding operations.

3. OBJECTIVESto… OBJECTIVES
Describe truing, dressing, and balancing of grinding wheels.
Distinguish the difference between the objectives of truing and dressing a grinding wheel.
Correctly position a single-point diamond dresser in relation to the grinding wheel.

4. Truing and Dressing TRUING, BALANCING & DRESSING
When a new wheel is installed, it must be trued before use, to bring every point on its cutting surface concentric with the machine spindle.
The cutting surface of a new wheel will run out slightly due to the clearance between the wheel bore & machine spindle.
Fig. L-51
Sketch, exaggerated for effect, showing a grinding wheel on a spindle. The gap under the spindle may be only a few thousandths of an inch but still enough to cause problems if the wheel is not trued to the center of the spindle.

5. Truing and Dressing TRUING, BALANCING & DRESSING
Dressing is the process of sharpening a grinding wheel.
In most grinding operations, small chips of workpiece material can become lodged in the cutting surface.
If the wheel bonding hardness is excessive, dulled abrasive grains can remain in the grinding wheel.
Both truing and dressing remove a certain amount of material from the grinding wheel.
Wheels should be trued & dressed only enough to establish concentricity or to expose new sharp abrasive grains to the workpiece.

6. Truing and Dressing TRUING, BALANCING & DRESSING
Optimal matching of grinding wheels to grinding operation results in a self-dressing condition.
Force of the grinding action is sufficient to release dull abrasive grains from the bond & keep the wheel sharp.
Need to retrue a grinding wheel typically relates to the losing of form control, as when the edges wear away an unacceptable amount.
Need to dress a grinding wheel is typically related to maintaining surface finish.

7. Truing and Dressing TRUING, BALANCING & DRESSING
Precision grinders are trued and dressed with single- or multiple- point diamond dressers.
Fig. L-52 Single-point diamond dresser. An important precaution in using such a dresser is to turn the diamond often to avoid grinding flats on it. This diamond is pointing to the right (Courtesy Desmond-Stephan Manufacturing Company).

8. Truing and Dressing TRUING, BALANCING & DRESSING
A cluster dresser may be wide enough to reach across the entire cutting surface of the wheel.
Traversing the dresser is the most common way to dress the grinding wheel
Fig. L-53 Cluster dressers have come into use mostly because several smaller diamonds are less expensive than one large diamond (Courtesy Desmond-Stephan Manufacturing Company).

9. Truing and Dressing TRUING, BALANCING & DRESSING
The dresser must be positioned off center and to the left of the wheel to prevent the dresser from getting caught and being pulled under the wheel.
Fig. L-54 This is one of several ways of mounting a dresser on a surface grinder. The dresser with its diamond is placed and magnetically secured on a clean magnetic chuck. Note that the diamond is slanted at a 15-degree angle and slightly past the vertical centerline of the wheel. (DoALL Company).

10. Truing and Dressing TRUING, BALANCING & DRESSING tab
When the dresser is cutting all around, the wheel has been fully trued.
Do not remove any more abrasive than is necessary to achieve concentric running of the cutting surface.
Truing may be done dry if the diamond allowed to cool a few seconds after each pass has been made.
If the truing is done with grinding fluid, flood the diamond continuously; otherwise, it could be fractured.
After truing & dressing, “break” sharp corners of the wheel with a dressing stick, leaving a small radius.

11. Balancing TRUING, BALANCING & DRESSING tab
An out-of-balance wheel can cause chatter marks in the workpiece finish.
Balancing is usually required on large wheels (over 14-in. diameter) but may not be required for smaller wheels.
Wheels are balanced on an overlapping disk balancing tool or parallel ways (Figs. L-63 & L-64).

12. Balancing TRUING, BALANCING & DRESSING tab
Fig. L-63 This type of balancing device with overlapping wheels or disks is quite common. It has an advantage in that it need not be precisely leveled
Fig. L-64 Balancing a wheel on two knife edges, as on this unit, is accurate because there is minimal friction. Of course, the unit must be perfectly level and true. Otherwise, the wheel may roll from causes other than being out-of-balance.

13. Balancing TRUING, BALANCING & DRESSING tab
Fig. L-65 With the weights between the vertical & horizontal centerlines the wheel should be in proper balance, stationary in any position. If not, a matched pair of differing balance weights should be used. (MAG Industrial Automation)