Here are some tips and guides for using tools to dress and true your grinding wheels for success from Norton Abrasives and Tools Illinois aka General Cutting Tools. Before a grinding wheel even touches a workpiece, it must first be trued and dressed, usually by a stationary diamond dressing tool. If you do this task right, then you can be sure that the wheel and parts coming off the machine are probably ground right. It’s true: everything the tool does to the wheel, the wheel does to the part. That’s why you should always begin troubleshooting grinding operations with a quick review of the truing and dressing processes. After all, truing and dressing are where the grinding process really begins.
By definition, truing ensures that the wheel is properly formed and that its spin is concentric to the mounting spindle. Dressing ensures that the abrasive particles are sharp during production grinding.
Each time a wheel is taken off a grinding machine, it must be re-trued. After production begins, the wheel should be occasionally dressed to restore its grains’ sharpness.
The rumors are true. Sharp diamond tools create sharp wheels, and dull tools produce dull wheels. Sharp wheels (also called open wheels) can remove the maximum amount of workpiece material during grinding. In lay terms, grinding with a sharp wheel is often fast and easy. By contrast, dull wheels (also called closed wheels) remove less material, often making grinding slow and hard. In addition to cutting less, dull abrasives literally rub the part and create smoother or lower surface-finish readings on the workpiece(s).
Sharp, open wheels are generally the preferred wheel condition. They tend to produce higher surface-finish readings and may require some intentional dulling to lower finish readings.
Creating an open (sharp) wheel is easy: Either 1) use a new stationary dressing tool or 2) move a tool – new or old – fast across the grinding wheel. Closed wheels simply require the opposite: 1) Use a dull tool, or 2) move the tool slowly across the wheel.
To ensure that your tools last a long time, pay close attention to some key parameters when dressing conventional wheels:
Wheel removal per dress pass. On aluminum oxide wheels, we recommend removing 0.001 inches (on the wheel radius) per dress pass. Reduce this amount by 25 percent when dressing silicon carbide or seeded-gel (SG) wheels, and reduce it by 50 percent when dressing Norton® Altos® (self-dressing ceramic aluminum oxide) wheels.
- Taking off too much wheel per dress pass overheats the diamond and often causes chipping.
- Taking off too little per dress pass, the sound of the dress to get louder, the finish tends to drop, and size/taper issues become evident.
The speed at which the tool moves across the wheel. Run tools using a single diamond at one speed across the wheel, and those using multiple diamonds three times faster. Remember, the slower a tool moves across the wheel, the lower the part’s surface-finish readings will be:
- For single points, chisels and cone point tools – Traverse Rate (the speed the tool moves across the wheel) in inches per minute = 0.006 x grinding wheel RPM*.
- For blades, grit (nib) tools and clusters – Traverse Rate (the speed the tool moves across the wheel) in inches per minute = 0.018 x grinding wheel RPM*.
* To calculate wheel RPM, divide Wheel SFPM (surface feet per minute) by (0.2618 x wheel diameter).
Avoid power dressing. If you need to reduce new wheel truing times, use an old tool as a roughing tool and save new(er) tools for production.
Creating Wheel Conditions
Open (Sharp) Wheel
- Generally preferred wheel condition
- Creates maximum wheel material removal
- Typically requires a new dressing tool
- Move the tool faster across the wheel
- Typically produces high finish readings
Closed (Dull) Wheel
- Wheel conditioning you may need
- Minimum wheel material removal
- Typically requires a worn dressing tool
- Move the tool slower across the wheel
- Produces lower finish readings