Feeds and speeds

Spindle RPM and feed rate for an end mill or router bit from surface speed and chip load.

Inputs

Surface speed

Use the tool maker’s chart first. Carbide in 6061 aluminum is often 600–1500 SFM; hobby routers run lower.

Tool diameter

Flutes

Chip load

Maximum spindle speed

Result

Spindle speed

7,639

Feed rate: 15.28
Actual surface speed: 500

How it’s calculated

Formula

n = \frac{v_c}{\pi D} \quad (\text{revolutions per unit time; RPM} = 60\,n \text{ with } n \text{ in rev/s})

v_f = n \times z \times f_z

With your numbers (converted to SI units)

n = \frac{2.54\,\text{m/s}}{\pi \times 0.00635\,\text{m}} = 127.3

v_f = 127.3 \times 2 \times 2.54 \times 10^{-5}\,\text{m} = 0.006468\,\text{m/s}

What it means

Surface speed is how fast the cutting edge moves through the material, and chip load is how thick a chip each flute takes. Too little chip load rubs instead of cutting and dulls the tool; too much breaks it. If the spindle can’t reach the ideal RPM, keep the chip load and accept the lower feed rate.

Assumptions

Tool maker’s values for full slotting are a safe start; reduce chip load for long, thin tools.

Learn the concepts behind this on resources.simbotics.org · All formulas