Automobile & Light Truck Certification Test A5 BrakesMachiningMedium
A technician is machining a brake drum and observes that the drum's friction surface is glazing over, appearing shiny and hard, rather than producing a clean metal finish. What adjustment should the technician make to the lathe settings to correct this condition?
- ADecrease the feed rate.
- BIncrease the spindle speed.
- CUse a duller cutting bit.
- DIncrease the depth of cut.
Show answer & explanationAnswer & explanation
Correct answer: D. Increase the depth of cut.
Glazing often occurs when the cutting tool is rubbing rather than cleanly cutting the material. Increasing the depth of cut allows the tool to engage more aggressively, getting 'under' the glazed surface and promoting proper chip formation for a clean finish.
Why the other options are wrong
- A. Decreasing the feed rate can also lead to rubbing and glazing, as the tool spends more time in contact with the same spot without removing material.
- B. Increasing spindle speed can exacerbate glazing by increasing friction and heat.
- C. Using a duller bit would worsen the problem, as dull bits are prone to rubbing and glazing.
Brake Drum Glazing
A condition during brake drum machining where the friction surface becomes shiny and hard, indicating the cutting tool is rubbing rather than cutting cleanly, often due to improper lathe settings.
- Results in poor surface finish.
- Can be caused by insufficient depth of cut or incorrect feed/speed.
- Requires adjustment to lathe parameters for proper material removal.
Memory trick: Rubbing makes it shine, but cutting makes it fine!