MakerKiln

CNC Feeds & Speeds

RPM, feed, plunge, depth of cut, and stepover from real chip-load math — sized to your machine. Start at 50–70% and climb.

Your machine

Tool & material

Spindlerpm
—
Feed—
Plunge— mm/min
Cut— DOC · step —

Roughing starting points from standard chip-load tables — your tooling, workholding, and dust extraction will move them. Climb in from 50–70%.

computed in this browser only

Local onlyThe chip-load tables and formulas are JavaScript in this tab. Your machine profile stays in this browser's local storage — nothing is uploaded, and the page works offline once loaded.

Feed-rate numbers from forums never transfer, because a feed rate is downstream of three things that differ machine to machine: spindle speed, tool geometry, and rigidity. What does transfer is chip load — the bite each flute takes per revolution. This calculator starts there: it derives RPM from the material's cutting speed and your end mill's diameter, clamps it to what your spindle can turn, then builds the feed from chip load × flutes × RPM, derated for machine class. Depth of cut and stepover follow the same scaling.

The table covers the hobby-CNC bench: softwood, hardwood, MDF and plywood, cast acrylic, HDPE and Delrin, 6061 aluminum, and 360 brass, across 3018-class machines, Shapeoko-class benchtops, and rigid industrial frames. Every number is a roughing starting point, not a promise — run the first cut at 50–70% feed and climb while the sound stays right.

Questions this tool gets asked

How do I calculate CNC feeds and speeds?

Two formulas do the work. RPM comes from the material's cutting speed and your tool's diameter: RPM = (cutting speed × 1000) ÷ (π × diameter). Feed rate comes from chip load: feed = chip load per tooth × number of flutes × RPM. This calculator applies both, clamps RPM to what your spindle can actually turn, and derates feed for less rigid machines.

What is chip load and why does it matter?

Chip load is how much material each cutting edge removes per revolution, in mm per tooth. Too low and the tool rubs instead of cutting — heat, dull edges, burnt wood, melted acrylic. Too high and it chatters or snaps. It is the number that transfers between machines, which is why this calculator computes feed from it rather than quoting someone else's feed rate.

Why does my small hobby machine get slower numbers?

Rigidity. A 3018-class machine flexes under cutting forces that a Shapeoko shrugs off and an industrial machine doesn't notice. The same chip load that cuts cleanly on a rigid machine becomes chatter and lost steps on a light one, so the calculator derates feed and depth of cut by machine class. Start at 50–70% of the suggestion and climb.

Why is my acrylic melting instead of cutting?

Counter-intuitively, melting usually means you are feeding too slowly, not too fast. When chips are too thin the tool rubs and heats the plastic until it welds back together. Increase feed or drop RPM to thicken the chip, and use a single-flute (O-flute) bit so each chip has room to escape.

What depth of cut and stepover should I use?

A common starting point is depth of cut around half the tool diameter in wood, a third in plastics, and a tenth in aluminum on hobby machines, with stepover around 40% of diameter for roughing. This calculator scales those by material and machine class. For finishing passes, drop stepover to 10% and take a light final depth.

Does anything I enter leave my browser?

No. The tables and formulas are JavaScript in this tab, your machine profile is remembered in this browser's local storage only, and the page works offline once loaded. Nothing is uploaded.

Why does my CNC bit burn the wood?

Burning means rubbing: the chip load is too small, so the edge scrapes and heats instead of cutting. Causes in order of likelihood — feed too slow for your RPM (the classic 'slowed it down to be safe' trap), a dull bit, dwelling in corners, and re-cutting packed chips in a slot. Fix it by raising feed or lowering RPM to restore chip load — the calculator above computes the balanced pair for your machine class.

What RPM and feed rate for a 1/8 inch end mill?

On a Shapeoko-class machine with a 2-flute 1/8 inch bit: softwood ~30,000 RPM at 3,600 mm/min; hardwood ~28,000 at 2,900; cast acrylic ~20,000 at 2,800 with a single-O flute preferred; 6061 aluminum ~12,000 at 700 with lubricant. A 3018-class machine takes roughly half those feeds. All of these come straight from the chip-load math above — set your material and machine and read your pair.

How deep should a CNC cut per pass?

Rules of thumb for roughing: about half the tool diameter in wood and MDF, a third in plastics, and a tenth in aluminum on hobby machines — so a 1/8 inch bit takes ~1.6 mm passes in wood but only ~0.4 mm in aluminum. Rigid machines can push deeper; 3018-class machines should take 30% less. The Cut tile above computes DOC and stepover for your exact bit and machine.

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