Abrasive Wheels Training Certificate Safe Mounting & Dressing Procedures — Questions and Answers
Question 1: Under PUWER 1998, who is authorised to mount abrasive wheels in the UK?
- Only a person who has received adequate instruction and training — an 'appointed person' designated by the employer (Correct answer)
- Any employee who has used an angle grinder before
- Only a qualified mechanical engineer
- Any person over 18 years of age
Correct answer: Only a person who has received adequate instruction and training — an 'appointed person' designated by the employer
PUWER 1998 requires that only persons who have received adequate instruction and training — typically designated as an 'appointed person' or 'competent person' for abrasive wheel mounting — may mount abrasive wheels. This applies to both angle grinders and bench grinders. Untrained mounting is a legal offence.
Question 2: What checks must be made before mounting an abrasive wheel?
- Ring test, visual inspection for cracks/damage, check wheel specification matches machine speed rating, check bore size matches spindle (Correct answer)
- Visual inspection only
- Check the expiry date on the wheel packaging only
- Only verify the wheel diameter is correct
Correct answer: Ring test, visual inspection for cracks/damage, check wheel specification matches machine speed rating, check bore size matches spindle
Before mounting: (1) perform the ring test; (2) visually inspect for cracks, chips, or damage; (3) confirm the wheel's maximum RPM rating exceeds the machine spindle speed; (4) verify the bore size matches the spindle; (5) check the wheel is the correct type and specification for the intended work. All checks must be completed.
Question 3: What is the purpose of blotting paper (compressible washers) between the wheel flanges and the abrasive wheel?
- To distribute clamping pressure evenly across the wheel face, preventing stress concentration and cracking when flanges are tightened (Correct answer)
- To prevent the wheel from loosening due to vibration during use
- To provide electrical insulation between the wheel and machine
- To absorb coolant and prevent it reaching the spindle bearing
Correct answer: To distribute clamping pressure evenly across the wheel face, preventing stress concentration and cracking when flanges are tightened
Blotting paper (or paper, felt, or rubber) washers distribute the clamping load from the flanges uniformly across the wheel face, preventing point-loading stress concentrations that could crack the wheel when the flanges are tightened. They also provide slight damping and protect the wheel face from direct hard metal contact.
Question 4: How should the flanges (clamping plates) that retain an abrasive wheel be sized?
- Each flange must be at least one-third of the wheel diameter and of equal size; the recessed face must bear on the wheel (Correct answer)
- Flanges may be any size provided the wheel does not slip
- Only the outer flange needs to be at least one-third diameter; the inner flange can be smaller
- Flanges must be exactly equal to the wheel diameter to provide full face support
Correct answer: Each flange must be at least one-third of the wheel diameter and of equal size; the recessed face must bear on the wheel
Regulations and standards require that both flanges be at least one-third the wheel diameter and of equal diameter. Undersized flanges concentrate the clamping force near the bore, creating stress and leaving the outer portion of the wheel unsupported. Recessed flanges must have their flat face in contact with the wheel.
Question 5: In which direction should the flange nut be tightened on a right-hand grinding spindle?
- Clockwise (right-hand thread) — the grinding reaction torque self-tightens a standard right-hand thread (Correct answer)
- Anti-clockwise — the wheel must be tightened against the direction of rotation
- Direction does not matter as the nut is locked with a split pin
- The nut should be left slightly loose to allow wheel expansion during use
Correct answer: Clockwise (right-hand thread) — the grinding reaction torque self-tightens a standard right-hand thread
On a standard right-hand (clockwise) rotating spindle, the thread is RIGHT-HAND so that the cutting reaction torque tends to self-tighten the nut. This prevents the nut loosening under load. However, angle grinders with left-hand spindle threads (to self-tighten with the rotation direction) use left-hand thread nuts — always check the machine manual.
Question 6: What is the maximum permissible gap between the abrasive wheel and the work rest on a bench grinder?
- 3mm (approximately 1/8 inch) to prevent the workpiece being drawn between the wheel and rest (Correct answer)
- No more than 10mm to allow large workpieces to be positioned
- 5mm is acceptable for wheels below 200mm diameter
- There is no standard for work rest gap — it is operator preference
Correct answer: 3mm (approximately 1/8 inch) to prevent the workpiece being drawn between the wheel and rest
The work rest gap must not exceed 3mm (BS 4481 and HSE guidance). A larger gap allows the workpiece to be drawn or jammed between the wheel and rest, potentially causing the wheel to shatter. The work rest should be adjusted after each wheel dress as the wheel diameter reduces.
Abrasive Wheels Training Certificate Safe Mounting & Dressing Procedures
Under PUWER 1998, who is authorised to mount abrasive wheels in the UK?