Abrasive Wheels Training Certificate Mounting and Balancing — Questions and Answers
Question 1: What is the primary purpose of blotters (compressible washers) when mounting an abrasive wheel?
- To increase the speed of the wheel
- To distribute clamping pressure evenly and prevent stress concentration (Correct answer)
- To make the wheel easier to remove
- To reduce the noise during grinding
Correct answer: To distribute clamping pressure evenly and prevent stress concentration
Blotters (compressible washers made of paper or card) are placed between the flanges and the wheel to distribute clamping pressure evenly across the wheel surface. This prevents localised stress points that could cause the wheel to crack.
Question 2: When tightening the spindle nut on an abrasive wheel, how tight should it be?
- As tight as possible using a pipe wrench for extra leverage
- Hand tight, then one quarter turn with a spanner (Correct answer)
- Finger tight only
- Torqued to exactly 50 Nm as per BS EN 12413
Correct answer: Hand tight, then one quarter turn with a spanner
The spindle nut should be hand tight plus approximately one quarter turn with a suitable spanner. Over-tightening can cause excessive stress on the wheel, potentially leading to cracking and catastrophic failure during use.
Question 3: What is the recommended standing position when first starting an abrasive wheel after mounting?
- Directly in front of the wheel to observe it closely
- To one side of the wheel, out of the plane of rotation (Correct answer)
- Behind a colleague for protection
- It does not matter where you stand
Correct answer: To one side of the wheel, out of the plane of rotation
After mounting a new wheel, the operator should stand to one side, out of the plane of rotation, when first starting the machine. If the wheel has an undetected defect, fragments will fly outward in the plane of rotation. HSE guidance specifically recommends this precaution.
Question 4: What minimum period should a newly mounted vitrified abrasive wheel be allowed to run at full operating speed before use?
- 10 seconds
- 30 seconds
- 1 minute (Correct answer)
- 5 minutes
Correct answer: 1 minute
HSE guidance recommends that a newly mounted vitrified wheel should be run at full operating speed for at least 1 minute before applying any work. For resinoid-bonded wheels, the recommended time is 30 seconds. This allows any defective wheel to fail before the operator approaches.
Question 5: What is the maximum permissible gap between the wheel and the work rest (toolrest) on a bench grinder?
- 1 mm
- 2 mm (Correct answer)
- 5 mm
- 10 mm
Correct answer: 2 mm
According to HSE guidelines, the gap between the abrasive wheel and the work rest should not exceed 2 mm. A larger gap increases the risk of the workpiece being drawn into the gap and jamming, which could cause the wheel to shatter.
Question 6: What is the correct procedure if an abrasive wheel is found to be out of balance after mounting?
- Continue using it as balance does not affect safety
- Add counterweights to the flanges using adhesive tape
- Use the adjustable balance weights in the wheel's balancing hub or dress the wheel (Correct answer)
- Increase the spindle speed to compensate for the imbalance
Correct answer: Use the adjustable balance weights in the wheel's balancing hub or dress the wheel
An out-of-balance wheel should be corrected using the adjustable balance weights in the wheel's balancing hub, or by dressing the wheel. An unbalanced wheel causes vibration, poor surface finish, premature bearing wear, and increases the risk of wheel failure.
Abrasive Wheels Training Certificate Mounting and Balancing
What is the primary purpose of blotters (compressible washers) when mounting an abrasive wheel?