Compréhension d'une consigne technique en anglais
A Burkinabè trainee reads this workshop instruction before assembling a bracket: "Before drilling, clamp the workpiece firmly to the bench. Use a 6 mm pilot bit first, then enlarge to 10 mm. Do not exceed 800 rpm when drilling steel, and apply cutting fluid continuously. Check the hole diameter with a caliper after each pass. If the bit squeals, stop the machine, let it cool, and reduce the speed." The trainee plans to drill directly with the 10 mm bit at 1400 rpm and without fluid, arguing that this saves time. He also says he will check the diameter only at the end.
1. List the safety and quality requirements stated in the instruction, and identify every point where the trainee's plan departs from them.
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Requirements stated in the text:
- Clamp the workpiece firmly before drilling.
- Drill a 6 mm pilot hole first, then enlarge to 10 mm.
- Do not exceed 800 rpm on steel.
- Apply cutting fluid continuously.
- Check the hole diameter with a caliper after each pass.
- If the bit squeals, stop, let it cool, and reduce speed.
Departures in the trainee's plan:
- He skips the pilot hole (point 2), which increases the risk of the bit wandering and of an oversized hole.
- He runs at 1400 rpm, well above the 800 rpm limit (point 3), which overheats the bit.
- He uses no cutting fluid (point 4), worsening heating and chip evacuation.
- He checks only at the end, so a defect cannot be corrected in time (point 5).
Conclusion: the plan contradicts four of the six requirements and saves no real time, since a ruined hole means starting again.
2. Explain in English, in your own words, why the pilot hole and the speed limit matter, and what the trainee should do if the bit squeals.
Read the worked answer
Model answer (English):
A pilot hole matters because a small 6 mm bit is stiffer and easier to guide than a 10 mm bit. It starts the hole accurately, prevents the drill from wandering on the surface, and reduces the load on the larger bit during the second pass. The final hole is therefore rounder and closer to 10 mm.
The speed limit matters because drilling steel generates heat. Above 800 rpm the bit and the workpiece heat up quickly, the cutting edges lose their hardness, and the bit can burn or break. Cutting fluid carries heat away and helps remove chips.
If the bit squeals, the trainee must stop the machine immediately, wait for the bit to cool, and reduce the spindle speed before restarting. He should not add force or continue drilling, because squealing usually means the bit is overloaded or misaligned.
Quality point: checking the diameter after each pass lets him correct the size before the hole is finished, which is cheaper than scrapping the part.