Wheel Speed and Wheel Guards SAFETY FIRST
The same general rules of safety apply to grinding machines as apply to other machine tools, but there are additional hazards because of the typically high speed of grinding wheels, which can store a great deal of energy.
If a grinding wheel becomes cracked, it can fly apart, ejecting chunks of wheel like missiles.
To reduce the safety hazards from wheel explosions,wheel guards (Figure L-34) are used on nearly every type of grinding machine.
All grinding wheels are rated at a specific maximum rpm. Exceeding rated speeds can cause a wheel to fly apart.
Always check rated speeds marked on the wheel blotter and never operate any grinding wheel beyond its stated maximum
The American National Standards Institute (ANSI) has adopted a specific set of standards, “Safety Requirements for the Construction, Care, and Use of Grinding Machines” (ANSI B11.9-1975, revised 2005). This document incorporates the earlier standards that specifically covered
only grinding wheel safety.
Seven additional ANSI B5 standards applying to specific designs of grinding machines were revised in 1992 and 1994.
Ring Testing a Grinding Wheel A vitrified bond grinding wheel can be “ring tested” for possible cracks (Figure L-35).
Hold the wheel on your finger or on a small pin. Tap the wheel lightly with a wooden mallet orscrewdriver handle. A good wheel will give off a clear ringing sound, whereas a cracked wheel will sound dull. If you discover a cracked wheel, advise your instructor or supervisor
Figure L-35 Making a ring test on a small wheel. immediately. Large grinding wheels may be ring tested while resting on the floor or being supported by a sling. Ring tests should be made a total of four times, indexing the wheel in 90-degree increments. Grinding Wheel Safety Rules
1. Handle and store grinding wheels carefully (Figure L-36).
2. Never use wheels that have been dropped.
3. Inspect all wheels for cracks or chips before mounting.
Ring test them.
Figure L-36 Store extra wheels in a cabinet. The main requirement is to keep the wheels separate or protected, and off the floor ( Asnuntuck Community College).
4. Do not alter a wheel to fit the grinding machine, and do not force it onto the machine spindle.
5. Make sure that the operating speed never exceeds the maximum allowable operating speed of the wheel.
6. Ensure that mounting flanges (Figure L-37) have equal and correct diameters. The bearing surfaces must be
clean for using mounting flanges.
7. Use mounting blotters unless the wheel is designed for some other mounting method.
8. Do not overtighten the mounting nut.
9. If the machine is a pedestal or bench grinder, adjust the work rest properly, just clear but not to exceed -in. clearance.
10. Do not grind on the side of a straight wheel (Figure
There are certain detailed exceptions to this rule. In applications such as shoulder and form grinding, some amount of side grinding takes place.
11. Use a safety guard that covers at least half of the grinding wheel, and do not start the machine until the guard is in place.
12. Allow the grinding wheel to run at least one minute before using it to grind (with the guards in place, of course), and do not stand directly in line with the rotating grinding wheel.
13. Always wear approved (ANSI Z-87.1) safety glasses or
other approved eye protection.
14. Use the correct wheel for the material you are grinding.
Overtightening the nut could spring the flanges and perhaps
even crack the wheel. (Follow the wheel manufacturer’s torque
Never grind on the side. Cylinder wheels, cup wheels (both
straight and flaring), and segments or segmental wheels (shown
here without the holder) are all designed for safe side grinding.