Cutting-Off Wheel Breakages - Causes and Cures

Play it Safe at the Wheel - 100 Years of Abrasives Safety Leadership

 

When a cutting-off wheel breakage occurs, it is natural to assume that the wheel is at fault. In most instances, this is simply not the case. There are many factors that can cause a wheel to break during use, from over speeding the wheel to an improperly clamped workpiece.

 

To better understand the causes and cures of cutting-off wheel breakages, read and follow the information below.

 

Wheel Breakages

 

The principal causes of wheel breakage on cut-off machines are:

  • A). Excessive Wheel Speed
  • B). Improper Mounting of the Wheel
  • C). Work Improperly Clamped
  • D). Abusive Operation
  • E). Improper Machine Conditions
  • F). Unequal Coolant Distribution
  • G). Excessive Wheel Feed into Work
  • H). Wheel Grade Too Hard

 

 Norton cut-off wheels

 

a). Excessive Wheel Speed

 

The maximum speed specified by the wheel manufacturer for the wheel to be used must not be exceeded.

 

b). Improper Mounting of the Wheel

 

Investigation of breakages using abrasive cutting-off wheels have revealed the following conditions for improper mounting.

 

1. Flanges not matched either in diameter or recess. This causes a bending stress on the wheel that may distort the wheel or cause it to be broken (see Figure 1). The flanges should be of equal diameter and recessed to produce equal and opposite clamping force on bearing areas (see Figure 2). 

 

Incorrect and correct demonstration of flange diameter

 

2. Excessive tightening of the spindle end nut may distort the flanges and result in wheel breakage (see Figure 3).

 Distorted flanges

 

c). Work Improperly Clamped

 

The work holder should be of proper design and of adequate size for the complete range of work for which the cutting-off machine is designed. If the work is allowed to shift or the pieces cut off do not fall away properly, the wheel may be “pinched;” this is a major cause of wheel breakage.

 

Incorrect and correct way to clamp the bar

 

 If the bar or tubing cut is slightly warped, it should be clamped in such a manner that the convex side is down and is in contact with the work support. Otherwise, when the piece is cut off, the bar or tubing may drop slightly, “pinching” the wheel (see Figure 4).

 

d). Abusive Operation

 

Cutting-off wheels are thin and do not have great lateral strength. Care should be taken to avoid twisting, cocking, cramping, or exerting any pressure on the side of the wheel. This is particularly true on portable cutting-off machines where the work is held and the wheel is guided by hand or on operations where the work is not clamped. On such operations, only reinforced wheels should be used. Attempting to cut work beyond the capacity of the wheel or the machine may cause wheel breakage.

 

E). Improper Machine Conditions

 

Loose wheel spindle, excessive end play, and loose or vibrating machine parts such as the work-table and the work holder may cause the wheel to bend in the cut and break. If the machine is underpowered for the job or has loose belts to the extent that the wheel slows down or stalls in the cut, there is a possibility of the wheel breaking.

 

It is unsafe and uneconomical to perform cutting-off operations which exceed the capacity of the machine. Table saws normally used in woodworking operations should never be used for cutting-off operations with abrasive wheels. These machines are generally not properly guarded, flanges are inadequate, and work holding devices are not suitable.

 

F). Unequal Coolant Distribution

 

When cutting wet, adjust the jets to direct the coolant so that it flushes both the wheel and the work at the same time. Use a generous flow of coolant for best results in abrasive cutting. It is essential that equal amounts of coolant are applied to each side of the wheel; otherwise, the periphery of the cutting-off wheel will wear irregularly, as shown in Figure 5. Excessive grooving of the wheel may be an indication that more coolant is required or possibly that the wheel grade is too soft. Coolant should be turned off before stopping the wheel so that the excess coolant will be centrifugally spun from the wheel.

 Regular and irregular wear on the periphery of the wheels

Wheels numbered 1, 2, and 3 will cut straight. Wheel  number 1 is good for cutting steel tubing. Unequal flow of coolant will result in irregular wear of the wheels on the periphery, as shown in wheel number 4 and 5. Such wheels will not cut straight.

 

Water, mixed with a reputable manufacturer’s grinding compound, is recommended as a coolant. The compound also acts as a rust inhibitor for both the cutting-off machine and the workpiece. The coolant tank must be kept clean and filled to the top to ensure that the pump will supply a generous flow.

 

G). Excessive Wheel Feed into Work

 

Jamming or feeding the work into the wheel too fast will cause excessive strain on the wheel and may result in wheel breakage, particularly with machines which feed the wheel into the work hydraulically.

 

H). Wheel Grade Too Hard

 

The use of a wheel of too hard a grade will generate excessive heat, which in turn will burn the bond on the wheel edges, causing chipping and eventually wheel breakage.

 

 

Information is the key to safety. Knowing and following the rules will keep you safe at the wheel. For more safety resources, view our safety articles.

 

For additional information on this topic or if you need any other abrasive safety information, please review the Norton Product Safety page, ANSI, OSHA, and all literature provided by the abrasive wheel and machine manufacturer. You may also contact the Saint-Gobain Product Safety Department at (508) 795-2317, fax: (508) 795-5120, or contact your Saint-Gobain Abrasives representative with any safety related questions.