Reducing Bushing; Friend or Foe?

Roger E. Cloutier, Senior Product Safety Engineer

Saint-Gobain Abrasives, Inc.

 

Over the years, we have received several requests concerning the rules regarding if and when a reducing bushing can be used to mount a grinding wheel onto a machine. To provide general rules for using reducing bushings let us review the current ANSI B7.1-2000 standards.

Section 1.2.69 of ANSI B7.1 defines reducing bushings as: Reducing bushings are inserts or devices used to reduce the hole size in a grinding wheel so that it can be mounted on a smaller diameter spindle. Section 6.5 continues to discuss reducing bushings and E6.5 explains the discussion in a practical application:

6.5 Reducing Bushings

Reducing bushings shall be specifically designed, properly manufactured and fitted when used in abrasive wheels. The bushing shall fit freely on the spindle and maintain proper clearance under all conditions. Minimum machine spindle size as shown in table 1, page 34, should not be violated. Reducing bushings shall not be used to mount a larger abrasive wheel on a grinder than those for which the grinder was designed. When a reducing bushing is used in the wheel arbor hole, it shall not exceed the width of the wheel and shall not contact the flanges. Loose reducing bushings (not mechanically held) should not be used with wheels less than 1/8" in thickness. Separate reducing bushings, unless supplied or recommended by the abrasive wheel manufacturer, shall not be used to adapt larger hole abrasive wheels to portable, hand held tools.

E 6.5 Reducing Bushings

If a reducing bushing is wider than the wheel in which it is used, it will interfere with proper tightening of the flanges against the wheel. The power required to drive a grinding wheel is transferred through the flanges. If this power is partially or completely transferred through the reducing bushing, wheel failure may result. Only an appropriate reducing bushing may be used to compensate for an oversize arbor hole, and substitutes, such as flat shim stock, must not be used.

The key points of the ANSI B7.1 and our recommendations are:

  • Never mount and use a wheel on a machine not designed and guarded for that wheel.
  • Use only the proper type of reducing bushings (supplied or recommended by the abrasive wheel or machine manufacturer).
  • Never allow reducing bushings to interfere with the proper wheel mounting. Reducing bushings cannot be thicker than the wheel (bushings thinner than the wheel are allowed).
  • Mounting flanges must be the correct type/size for the wheel being mounted.
  • The reducing bushing MUST NEVER be allowed to contact the flange.
  • Never mount a grinding wheel onto a portable machine with a reducing bushing.

Table 1, of ANSI B7.1 displays the minimum diameter of a machine spindle as it relates to wheel thickness and diameter.

Horror story: A customer used a reducing bushing to mount a wheel onto a machine with a hole larger than the machine’s wheel mounting flanges. Upon starting the machine, the abrasive wheel “fell” off the machine causing an injury. BE CAREFUL when using reducing bushings. You never want to eliminate the flange’s recess, exceed the machine flange’s diameter or negatively impact the proper mounting of an abrasive wheel. If you don’t know or are unsure of the proper mounting procedures for a wheel/machine with a reducing bushing, contact your abrasive supplier for additional information or assistance. Safety is as safety does!

 

Click to read Proper Mounting of a Grinding Wheel or Flanges: A Critical Link in Grinding Wheel Safety

 

For additional information on this topic or if you need any other abrasive safety information, please review ANSI, OSHA and all literature provided by the abrasive wheel and machine manufacturer. You may also contact the Saint-Gobain Product Safety Department at Tel. (508) 795-2317 or Fax. (508) 795-5120, email to nortonsafety@saint-gobain.com or contact your Saint-Gobain Abrasives, Inc. representative with any safety related questions.