Milling Chip Load Starting-Point Chart

What it is

Chip load (feed per tooth, IPT or fz) is how thick a chip each cutting edge takes. Too little and the edge rubs and wears; too much and the tool chips or breaks. Feed rate comes from chip load:

• Feed (IPM) = RPM × number of flutes × chip load (IPT)
• Metric: vf (mm/min) = n × z × fz (mm)

How to use it

Set RPM from the surface speed chart. Pick a starting chip load from the tool maker's data, or use the rough ranges below when none is at hand. Start at the low end, then raise feed while watching chip color, sound and finish. Correct for chip thinning when the radial width of cut is under half the diameter.

Approximate starting chip load, solid carbide end mills (in per tooth)

These are rough slotting-to-side-milling starting points only. Tool makers publish exact values by series, coating and engagement; their data governs.

Chip-thinning factor for light radial cuts

The factor is D ÷ (2 × √(D × ae − ae²)), where ae is the radial width of cut.

Key points

• Chip load scales roughly with diameter. A small tool takes a much smaller chip.
• HSS end mills generally run at lower speed than carbide; follow the HSS data, not carbide data.
• Long reach, poor workholding or a worn spindle call for lower chip loads.
• More flutes give a higher feed rate at the same chip load but less room for chips. In aluminum, 2 or 3 flutes are common for this reason.

Common mistakes

• Feeding too lightly to "be safe," which rubs, work-hardens stainless and wears the tool faster.
• Applying a slotting chip load to a light finishing pass without the chip-thinning correction.
• Counting flutes wrong on a variable-pitch or chipbreaker tool.

Governing standards: None. Tool manufacturer's speed and feed data governs.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.