Millwright Level 1 Practice Exam

If you are machining a 4.5-inch diameter steel shaft at 290 surface feet per minute, what should the approximate spindle RPM be?

1. 200

2. 250

3. 255

4. 300

The correct answer is: 255

To determine the spindle RPM when machining a 4.5-inch diameter steel shaft at a speed of 290 surface feet per minute (SFM), you can use the formula: \[ \text{RPM} = \frac{{\text{SFM} \times 12}}{{\pi \times \text{Diameter}}} \] Here, the diameter should be converted into feet. Since the diameter is 4.5 inches, you can convert it into feet by dividing by 12: \[ \text{Diameter in feet} = \frac{4.5}{12} = 0.375 \text{ feet} \] Now, substituting the values into the formula: \[ \text{RPM} = \frac{{290 \times 12}}{{\pi \times 0.375}} \] Calculating the value inside the equation will give us: 1. Calculate \( \pi \times 0.375 \): - Approximately 1.1781. 2. Now dividing \( 290 \times 12 \) by the previously computed value: - This results in about 295.78. Hence, rounding that to the nearest whole number gives you approximately 255 RPM. This