Abrasive Wheels Training Certificate Mounting and Balancing 2 — Questions and Answers
Question 1: What must be checked about the flanges before mounting an abrasive wheel?
- That they are painted the correct colour
- That they are clean, flat, undamaged, and of equal diameter (at least one-third of wheel diameter) (Correct answer)
- That they are made of plastic
- That they are larger than the wheel diameter
Correct answer: That they are clean, flat, undamaged, and of equal diameter (at least one-third of wheel diameter)
Flanges must be clean, flat, undamaged, and of equal diameter. The flange diameter should be at least one-third of the wheel diameter. Damaged or unequal flanges create uneven pressure distribution, which can cause the wheel to crack during operation.
Question 2: Why should an abrasive wheel never be force-fitted onto a spindle?
- It voids the manufacturer's warranty
- Forcing can crack the wheel, leading to catastrophic failure at operating speed (Correct answer)
- It makes the wheel spin faster than intended
- It is not a legal requirement, just best practice
Correct answer: Forcing can crack the wheel, leading to catastrophic failure at operating speed
Force-fitting an abrasive wheel can cause invisible internal cracks. When the wheel is spun at operating speed, centrifugal forces can cause these cracks to propagate rapidly, resulting in catastrophic wheel failure and potential serious injury or death.
Question 3: On a double-ended bench grinder, what is the purpose of the tongue guard (spark guard)?
- To collect metal filings for recycling
- To prevent sparks from reaching the operator and to limit the exposed portion of the wheel (Correct answer)
- To improve the quality of the grinding surface finish
- To cool the workpiece during grinding
Correct answer: To prevent sparks from reaching the operator and to limit the exposed portion of the wheel
The tongue guard (also called a spark guard or spark arrestor) serves to deflect sparks away from the operator and to limit the exposed portion of the wheel. It should be adjusted to within 6 mm of the wheel as the wheel wears down.
Question 4: What should be the maximum gap between the tongue guard and the abrasive wheel on a bench or pedestal grinder?
- 2 mm
- 6 mm (Correct answer)
- 10 mm
- 15 mm
Correct answer: 6 mm
The maximum gap between the tongue guard and the wheel should not exceed 6 mm. As the wheel wears and its diameter decreases, the tongue guard must be adjusted to maintain this clearance. This is separate from the 2 mm work rest gap requirement.
Question 5: What is the correct method for checking an abrasive wheel for cracks before mounting (the 'ring test')?
- Spin the wheel on its spindle and listen for unusual sounds
- Suspend the wheel on a pin or finger through the bore and tap gently with a non-metallic implement, listening for a clear ring (Correct answer)
- Drop the wheel from 1 metre onto a concrete floor
- Submerge the wheel in water and look for air bubbles
Correct answer: Suspend the wheel on a pin or finger through the bore and tap gently with a non-metallic implement, listening for a clear ring
The ring test involves suspending the wheel vertically on a pin or finger through the bore hole and tapping it gently with a non-metallic implement (such as a screwdriver handle). A sound, undamaged wheel produces a clear, metallic ring. A dull or dead sound indicates a crack.
Question 6: When mounting a new abrasive wheel, in what order should the following steps be performed?
- Mount wheel, tighten nut fully, connect power, run at speed
- Visual inspection, ring test, mount with blotters, tighten correctly, run idle at full speed standing to one side (Correct answer)
- Connect power, mount wheel, add blotters, tighten nut
- Ring test, force onto spindle, tighten with pipe wrench, test immediately on workpiece
Correct answer: Visual inspection, ring test, mount with blotters, tighten correctly, run idle at full speed standing to one side
The correct sequence is: (1) Visual inspection for damage, (2) Ring test to check for cracks, (3) Mount with blotters between flanges and wheel, (4) Tighten spindle nut correctly (hand tight plus quarter turn), (5) Run at full speed for the recommended idle period while standing to one side.
Abrasive Wheels Training Certificate Mounting and Balancing 2
What must be checked about the flanges before mounting an abrasive wheel?