1. What is a Speed and Feed Calculator for Lathe?

Definition: This calculator determines the optimal spindle speed (RPM) and feed rate (IPR) for lathe operations based on material, tool, and diameter.

Purpose: It helps machinists and CNC operators achieve efficient material removal while maintaining tool life and surface finish.

2. How Does the Calculator Work?

The calculator uses two fundamental formulas:

Where:

• \( RPM \) — Spindle speed (revolutions per minute)
• \( SFM \) — Surface feet per minute (material-specific cutting speed)
• \( D \) — Workpiece diameter (inches)
• \( IPR \) — Feed rate (inches per revolution)
• \( IPT \) — Feed per tooth (inches)
• \( Z \) — Number of teeth on the cutting tool

Explanation: The first formula converts SFM to RPM based on diameter. The second calculates feed rate from tool geometry.

3. Importance of Proper Speed and Feed

Details: Correct RPM and IPR settings prevent tool breakage, improve surface finish, optimize machining time, and extend tool life.

4. Using the Calculator

Tips: Enter the material's recommended SFM, workpiece diameter, tool's IPT value, and number of teeth. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Where do I find SFM values?
A: SFM depends on material and tool. Consult machining handbooks or tool manufacturer recommendations.

Q2: Why 3.82 in the RPM formula?
A: This constant converts SFM (feet/min) and diameter (inches) to RPM (rev/min): 12/π ≈ 3.82.

Q3: What's a typical IPT value?
A: IPT varies by tool and material. Carbide inserts might use 0.004-0.012", HSS tools 0.002-0.010".

Q4: How does diameter affect RPM?
A: Smaller diameters require higher RPM to maintain the same SFM. RPM is inversely proportional to diameter.

Q5: Should I adjust for roughing vs finishing?
A: Yes. Roughing typically uses higher IPT and lower SFM, while finishing uses lower IPT and higher SFM.