1. What is RPM in Machining?

RPM (Revolutions Per Minute) is the rotational speed of the cutting tool or workpiece in machining operations. Proper RPM calculation ensures optimal cutting conditions, tool life, and surface finish.

2. How Does the Calculator Work?

The calculator uses the RPM formula:

Where:

• \( SFM \) — Surface Feet per Minute (cutting speed)
• \( Diameter \) — Diameter of the cutting tool or workpiece in inches
• 4 — Conversion factor (12 inches/foot ÷ π ≈ 3.82, typically rounded to 4 for practical use)

Explanation: The equation converts surface speed at the tool's edge to rotational speed based on the tool diameter.

3. Importance of RPM Calculation

Details: Correct RPM is critical for achieving proper cutting speeds, preventing tool damage, maintaining dimensional accuracy, and optimizing machining efficiency.

4. Using the Calculator

Tips: Enter SFM (from material/tool recommendations) and tool/workpiece diameter in inches. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is SFM in machining?
A: SFM (Surface Feet per Minute) is the speed at which the tool's cutting edge moves across the workpiece surface.

Q2: Why does diameter affect RPM?
A: Larger diameters require slower RPM to maintain the same surface speed at the cutting edge.

Q3: What are typical SFM values?
A: SFM varies by material: 100-300 for aluminum, 50-150 for mild steel, 30-80 for stainless steel, depending on tool material.

Q4: When should I use exact vs rounded conversion factor?
A: For most practical applications, 4 is sufficient. Use 3.82 (12/π) when precision is critical.

Q5: How does RPM affect tool life?
A: Excessive RPM causes heat buildup and premature tool wear, while too low RPM reduces productivity.