CNC milling material selector, machinability compared across 14 materials
Tick the requirements your part actually has, strength, weight, corrosion resistance, temperature, food or medical contact, and the tool ranks candidates by a machinability index anchored to mild steel, not by which material happens to be popular.
Open the material selector A free account opens this tool. The interface is in English and nothing you enter leaves your browser.How it works
Three steps. The order matters: requirements first, machine settings second.
Tick what the part actually needs
Select any combination of strength, low weight, high temperature service, corrosion resistance, electrical conductivity, or food and medical contact. Leave everything unticked for a general overview across all fourteen materials.
Set quantity, budget and the type of machining
These three settings change how the fourteen candidates are weighted against each other. The same material can rank first for a one-off prototype and drop several places for a high-volume production run on a tight budget.
Read the ranked candidates and the comparison table
Each candidate shows its machinability index against the mild steel baseline, tool wear, coolant requirement and any dry-milling warning that applies to it, so the ranking is never just a name at the top with no explanation underneath.
Fourteen materials, one consistent scale
Mild steel is the fixed baseline at index 100. These are some of the materials ranked against it.
Built to separate real physics from catalogue marketing
Most bad material calls are not about strength. They are about heat, chip control and a catalogue number nobody checked.
One baseline, fourteen materials measured against it
Mild steel S235JR/1018 is fixed at index 100 by definition. Aluminium 6061-T6 comes out at 380, free-machining brass C360 at 320, Delrin (POM) at 350, while titanium Ti-6Al-4V falls to just 22, the lowest of the fourteen materials in the table. That is a spread of more than seventeen times in recommended cutting speed between the easiest and the hardest material here.
Coolant requirement stated as four honest tiers, not one blanket rule
Brass C360 needs no coolant at all, it is self-lubricating. Most steels and aluminium alloys treat coolant as a recommendation, dry milling is common practice, not a mistake. Stainless 304, 316 and titanium are different: flood coolant is mandatory, because dry milling there means work hardening, chewed-up tool life and, with titanium, a real fire risk from glowing hot chips. Engineering plastics get their own category, air blast only, because an ordinary oil-based coolant can craze a material such as polycarbonate.
Built-up edge and chip control flagged before they ruin a finish
Built-up edge happens when the material welds to the cutting edge instead of shearing cleanly, a known risk with ductile, low-silicon materials such as 5083 aluminium. Long ribbon chips are a separate hazard, able to wrap around the tool, the part or the spindle. Free-machining grades such as 303 stainless and C360 brass exist specifically to break the chip short instead.
Where the rules core has no answer, the tool says so
The EDi Brain rules core carries 282 records for sheet metal and five general DFAM rules, but checked directly, none for milling, while laser cutting already has 45. Rather than invent a milling rule ID that does not exist, the tool states plainly which numbers come from physical constants, density, thermal conductivity, typical yield strength, published in sources such as the ASM Handbook and MatWeb, and which are a summary of tool manufacturer catalogues, a starting point, not a lab measurement for your machine.
Frequently asked questions
What does the machinability index actually measure?
It is the classical AISI/SAE relative machinability scale, used in engineering for close to a century. Mild low-carbon steel is fixed at 100 by definition. A number above 100 means an easier cut, a higher recommended cutting speed and lower cutting forces; a number below 100 means the opposite. It is not a single official standard measured to the last digit, different tool manufacturer catalogues give close but not identical numbers because they depend on the specific tool, coating and test method.
Why is titanium so much harder to machine than aluminium?
Mostly thermal conductivity. Titanium Ti-6Al-4V conducts heat at only 6.7 watts per metre kelvin, about twenty five times lower than aluminium 6061 at 167 watts per metre kelvin, and nearly eight times lower than mild steel at 51 watts per metre kelvin. Heat generated at the cutting edge cannot move away through the material fast enough, so it stays concentrated right at the tool, wearing it out quickly and creating a genuine fire risk from hot titanium chips without flood coolant.
Why is stainless 316 harder to cut than 304?
The molybdenum that 316 carries, roughly two to three per cent, is what gives it its chloride and seawater corrosion resistance, and the same addition raises the material's toughness, which makes it a slower, more expensive cut. On the index used here 316 comes out at 36 against 45 for plain 304, and free-machining 303, with added sulphur for chip control, reaches 78. It is a classic engineering trade, better corrosion resistance bought with a harder machining process.
Does the tool tell me the spindle speed, feed rate or depth of cut?
No. It recommends a material, not machining parameters for a specific tool. Spindle speed, feed and depth of cut need the catalogue of the actual cutting tool you plan to use, or CAM software with a cutting database, that is a separate task outside what this tool does.
Why do 6061, 7075 and 5083 aluminium behave so differently under the same label?
They are different alloys with different alloying elements. 7075-T6 has a yield strength around 503 MPa, nearly double the 276 MPa of 6061-T6, but the higher copper content that gives it that strength also makes it more prone to stress corrosion cracking. 5083-H116 is a marine alloy with low silicon content, which makes it prone to built-up edge on the cutting tool rather than shearing cleanly, a real problem for fine detail and sharp internal corners, even though its saltwater resistance is excellent.
Can I trust these numbers for a load-bearing or medical part?
Treat them as an honest starting point, not a certificate. The ordinal ratings for corrosion resistance, temperature rating and price class are engineering judgement over published references, a relative ranking among the fourteen materials, not a value measured on your specific batch of raw material. For a load-bearing structure, an implant or a pressure vessel, check the material certificate and consult an engineer.
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