Question 1

How do I convert cutting speed to spindle RPM?

Accepted Answer

Spindle speed is n = Vc × 1000 / (π × D), where Vc is the cutting speed in m/min and D is the tool diameter in mm. For example, Vc = 100 m/min with a 10 mm cutter gives n = 100 × 1000 / (π × 10) ≈ 3183 rpm.

Question 2

How do I calculate the feed rate on a CNC?

Accepted Answer

The table feed is vf = n × fz × z, where n is the spindle speed in rpm, fz is the feed per tooth (chip load) in mm and z is the number of flutes. With n = 3183 rpm, fz = 0.05 mm and z = 2, vf = 3183 × 0.05 × 2 ≈ 318 mm/min.

Question 3

What is material removal rate (MRR)?

Accepted Answer

MRR is the volume of material removed per minute. For milling MRR = ap × ae × vf / 1000 in cm³/min, where ap is the axial depth of cut, ae the radial width of cut (both in mm) and vf the feed rate in mm/min. It indicates how hard the cut is working.

Question 4

What is the difference between feed per tooth and feed per revolution?

Accepted Answer

Feed per tooth fz (chip load) is how far the tool advances for each cutting edge; feed per revolution is f = fz × z for a z-flute tool. Feed rate vf is the feed per revolution multiplied by the spindle speed.

Question 5

What cutting speed and feed should I actually use?

Accepted Answer

The right values depend strongly on the workpiece material, the tool material and coating, and the rigidity of the machine and setup. Treat these results as a starting point and always prefer the tool manufacturer's recommended cutting data for your exact tool and material.

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