How to Safely Mount Grinding Wheels Used In Sets
Roger E. Cloutier, Senior Product Safety Engineer, Saint-Gobain Abrasives, Inc.
We receive calls from our customers asking us if they can mount several wheels onto a single arbor in sets. Some of the grinding applications where it is common to use multiple wheels on a single spindle are Centerless, Crank and Cam (bearing) grinding. What are the rules for mounting several wheels onto a spindle? What may happen if the correct procedures are not followed?
We have been asked, “In applications with multiple wheels mounted on a single spindle without spacers, can we mix and match grinding wheels from different sets, different abrasive manufactures, different batches, etc.?”
No, you cannot mix and match wheels from different sources. Multiple grinding wheels used in sets without spacers (for example many Centerless applications) must be manufactured and marked for use as a multiple wheel set. Each wheel in “multiple wheel sets” has special tighter side and hole tolerances. The sides must be parallel to each other and the holes must be perpendicular to the side of the wheel. Also, the wheels are “trued” and “balanced” as a set. Combining several grinding wheels and mounting them onto a single arbor when they are not designed and manufactured to be used as a “multiple wheel set” is dangerous for several reasons. The cross bending stresses applied to wheels with uneven sides, and wheels with sides not perpendicular to the wheels' hole can break even the strongest wheel. Slippage problems, irregular faces, and balance problems may also occur. As ANSI B7.1-2000, page 80 states, “When mounting wheels which have not been cemented together, or ones which do not utilize separate spacers, care must be exercised to use wheels specifically manufactured for that purpose.”
Another good question has been, “What are the requirements for applications with multiple wheels mounted between spacers on a single spindle?”
- When multiple wheels are mounted between a single set of flanges using spacers (for example cam grinding) the user must follow the ANSI requirements.
- For spacers less than .050" thick ANSI B7.1-2000, pages 79 and 80 states, “Spacers less than .050" thick, used between wheels which are mounted between a single set of flanges, shall be equal in diameter to the flanges. They shall be made of low compressibility material such as brass or soft copper. Blotter material shall NOT be used in place of or in conjunction with thin spacers.”
- For spacers thicker than .050" thick ANSI B7.1-2000, pages 79 and 80 states, “Spacers thicker than .050" may be steel and spacers thicker than 3/8" shall be made of steel. When steel spacers are used, their diameter shall equal flanges diameters, and the spacers shall be relieved so that bearing surfaces equal flange bearing surfaces. Blotters shall be used between spacers and wheels.”
Failing to follow this rule can lead to problems with the wheel slippage and wheel breakage.
Sometimes we receive questions like, “We have several thin cut-off wheels and would like to mount them onto a single spindle to create a thicker Type 1 wheel. Is that safe?”
No, that would be dangerous. If you need a cut-off wheel, purchase a cut-off wheel and if you need a thick Type 1 wheel, order a thick Type 1 wheel. Don’t try to “Rube Goldberg” a grinding set-up.
A gentleman was injured when his employer mounted two bench grinding wheels on a bench grinder/electric motor. The two wheels were on a short spindle (designed for a single wheel) and the single end nut would only thread onto the spindle by less than a single thread. The single end nut and one of the wheels fell off the machine (no wheel guard) causing the operator to be struck by
the wheel and injured.
The spindle length and machine wheel guard is an indicator of the size and number of wheels that can be safely mounted on a single spindle or machine.
- NEVER MOUNT THICKER OR MORE WHEELS THAN THE MACHINE SPINDLE IS DESIGNED TO HOLD!
- Never alter a machine with a longer spindle than the machine is designed to hold.
- Never cut guards away to use longer spindles or mount additional wheels onto a machine!
Improper wheel mounting can cause wheel breakage, personal injury and even death.
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 or contact your Saint-Gobain Abrasives, Inc. representative with any safety related questions.