Feed and Speed Calculator for Brass: Chip Load Chart & RPM
Brass machines beautifully and grabs unexpectedly. It is one of the few materials where the correct spindle speed is lower than most people's instinct, and where cutter geometry matters more than feed.
For brass, the recommended chip load runs from 0.038–0.064 mm per tooth on a 1/8″ cutter to 0.127–0.178 mm on a 1/2″. Typical spindle speeds sit between 8,000 and 14,000 RPM.
Your chip load is 0.1015 mm per tooth, which is within the recommended 0.076–0.127 mm range for brass with a 6.35 mm upcut spiral.
Brass. Brass machines cleanly but grabs. It cuts better at lower RPM than most people expect, and a cutter with no rake will resist snatching into the work.
Upcut spiral. The baseline the published charts assume. Chips are lifted clear of the cut, which keeps heat out of the workpiece at the cost of tear-out on the top surface.
How to cut brass on a CNC router → - the full how-to: which bit, workholding, chip evacuation and reading the cut.
How brass fails when the chip load is wrong
The characteristic failure is the cutter snatching - biting into the work and pulling itself in. Brass is soft enough that a cutter with aggressive positive rake can self-feed, which on a light machine means a sudden load spike and a broken tool.
Setting up a cut in brass
Run it slower than you would run aluminium. A cutter with neutral or slightly negative rake resists grabbing; this is why dedicated brass tooling exists rather than just reusing aluminium end mills. Chips come off as fine granules rather than curls, which is normal.
The thing most people get wrong
Free-machining brass and cartridge brass are very different to cut. If the chips are stringy rather than granular, you are on a higher-zinc alloy that behaves more like copper - expect it to be gummier and to load the flutes.
Chip-load reference for brass
Recommended chip load per tooth by cutter diameter, before any adjustment for depth of cut or bit geometry. Values between the 1/8″, 1/4″ and 1/2″ anchors are interpolated.
| Cutter diameter | Chip load (mm/tooth) | Chip load (in/tooth) |
|---|---|---|
| 1/16" (1.59 mm) | 0.038 – 0.064 | 0.0015 – 0.0025 |
| 1/8" (3.18 mm) | 0.038 – 0.064 | 0.0015 – 0.0025 |
| 4 mm | 0.048 – 0.080 | 0.0019 – 0.0032 |
| 6 mm | 0.072 – 0.120 | 0.0028 – 0.0047 |
| 1/4" (6.35 mm) | 0.076 – 0.127 | 0.0030 – 0.0050 |
| 8 mm | 0.089 – 0.140 | 0.0035 – 0.0055 |
| 3/8" (9.53 mm) | 0.102 – 0.153 | 0.0040 – 0.0060 |
| 1/2" (12.70 mm) | 0.127 – 0.178 | 0.0050 – 0.0070 |
These are estimates derived from published tooling-manufacturer data, not test results. Always prove a new setting on scrap first. Sources are listed on the methodology page.
Other materials
Already running a feed rate and want to know what chip load it produces? Use the chip load calculator.