Materials

CNC Machining Materials: Grade Property Data and Selection

Name: CNC machining grade property matrix
Creator: Meco
License: https://www.mecomeco.com/

Density, tensile, hardness, thermal conductivity, machinability index and carbide cutting speed for 33 machined grades, with the tolerance each one actually holds.

Full property matrix for 33 metal grades and 9 resins.

Achievable tolerance and Ra published per material, not one blanket figure.

ASTM, GB, JIS and EN grade equivalents cross-referenced.

Ask an Engineer About Your Material

CNC machined aluminum, steel, stainless and plastic parts in various grades

33 GradesWith Full Property Data

22–300%Machinability Range

±0.005 mmTightest Held, Ground

4 StandardsASTM, GB, JIS, EN

Reading Material Property Data Before You Pick a Grade

Four numbers decide most machining outcomes. Machinability index predicts cycle time and tool wear. Thermal conductivity predicts whether cutting heat leaves in the chip or stays at the tool tip. Hardness sets the cutting speed ceiling. Density converts a per-kilo stock price into a real per-part cost.

Those four explain almost every counterintuitive result on this page. Titanium Grade 5 is only twice the tensile strength of 6061 but costs eighteen times as much to buy and runs at a tenth the cutting speed, because 6.7 W/m·K of thermal conductivity means the heat has nowhere to go but the insert. Copper is soft and still machines poorly, because gummy chips weld to the edge.

The tables below give all four figures for every grade, plus the tolerance and surface finish each material realistically holds in one setup.

Easiest to Cut

C36000 Brass

Machinability 300%, 300–600 m/min carbide. The benchmark every other alloy is rated against.

Hardest to Cut

Ti-6Al-4V

Machinability 22%, 30–60 m/min. Thermal conductivity of 6.7 W/m·K is the reason.

Best Strength to Weight

7075-T6

572 MPa at 2.81 g/cm³. Higher specific strength than 316 stainless at a third the density.

Tightest Tolerance

±0.005 mm

Hardened 52100 or 440C, ground. Turned grades hold ±0.010 to ±0.020 mm.

Swipe for all four

Metal Grade Property Matrix

Every grade we cut, with the property data that predicts cycle time, cost and achievable tolerance. Machinability and cutting speed are the two columns that move your quote most.

Typical published values for the common temper or condition; verify against the mill certificate for your lot. Machinability is expressed as a percentage of AISI B1112 free-cutting steel at 100%; copper-alloy figures are converted from the C36000 = 100 copper scale, so treat cross-family comparisons as indicative. Cutting speeds assume uncoated or coated carbide in turning with flood coolant. Cost index is indicative raw stock cost per kilogram against 6061 at 1.0× and moves with market and section size.
Grade	Density g/cm³	Tensile MPa	Yield MPa	Hardness	Therm. Cond. W/m·K	Machinability	Carbide Vc m/min	Cost Index
Aluminum
6061-T6	2.70	310	276	95 HB	167	190%	300–900	1.0×
6063-T6	2.70	241	214	73 HB	201	200%	300–900	1.0×
6082-T6	2.70	310	260	95 HB	170	190%	300–800	1.1×
7075-T6	2.81	572	503	150 HB	130	140%	200–600	2.5–3×
5052-H32	2.68	228	193	60 HB	138	130%	250–700	1.2×
2024-T351	2.78	469	324	120 HB	121	170%	200–600	2–2.5×
Carbon Steel
1020 CD	7.87	420	350	121 HB	51.9	65%	120–200	0.7×
1035	7.85	550	460	163 HB	51.0	65%	110–190	0.7×
1045 CD	7.85	625	530	179 HB	49.8	57%	100–180	0.8×
Alloy and Free-Cutting Steel
12L14	7.87	540	415	163 HB	51.9	170%	150–280	0.9×
1215	7.87	540	415	167 HB	51.9	136%	140–260	0.9×
1144	7.86	690	620	197 HB	49.0	85%	120–200	1.0×
4140 / 42CrMo annealed	7.85	655	415	197 HB	42.6	65%	90–160	1.2×
4340 annealed	7.85	745	470	217 HB	44.5	55%	80–140	1.6×
40Cr / 5140 Q&T	7.85	980	785	207 HB ann.	44.0	60%	90–150	1.1×
52100 / GCr15	7.81	690 ann.	380 ann.	197 HB ann., 60–64 HRC hardened	46.6	40%	70–120	1.6×
Stainless Steel
303	8.00	620	415	228 HB	16.3	78%	120–200	2.4×
304 / 304L	8.00	515	205	201 HB	16.2	45%	90–160	2.5×
316 / 316L	8.00	515	205	217 HB	16.3	36%	80–150	3.2×
430	7.75	515	310	183 HB	26.1	54%	100–170	2.2×
420	7.75	655 ann.	345 ann.	195 HB ann., to 52 HRC	24.9	45%	80–140	2.6×
440C	7.65	760 ann.	450 ann.	269 HB ann., 58–60 HRC	24.2	40%	70–120	3.5×
17-4PH H900	7.80	1310	1170	40–44 HRC	17.9	40%	60–110	5×
2205 duplex	7.80	655	450	293 HB max	19.0	30%	50–90	4.5×
2507 super duplex	7.80	795	550	310 HB max	17.0	25%	40–80	7×
Brass
C36000	8.50	340–470	125–310	78–99 HB	115	300%	300–600	3.5×
C37700	8.44	360	140	78 HB	117	240%	250–500	3.5×
C46400 naval	8.41	400–600	170–455	55–180 HB	116	90%	150–250	4×
C48500 leaded naval	8.44	385–450	170–365	130 HB	116	210%	200–350	4.2×
Bronze
C63000 / QAl10-4-4	7.58	690–760	345–470	187–229 HB	39	90%	90–160	6×
C93200 / SAE 660	8.93	240	125	65 HB	47	210%	150–300	5×
C95400	7.45	585	250	170 HB	59	180%	120–220	5.5×
Copper
C10100 / TU1	8.94	220–380	70–330	40–95 HRF	391	60%	200–400	4.5×
C11000 / T2	8.89	220–390	70–330	40–95 HRF	388	60%	200–400	4.3×
C12200 / TP2	8.94	220–380	70–330	40–95 HRF	339	60%	200–400	4.5×
Titanium
Grade 2 / TA2	4.51	345	275	145 HB	16.4	40%	60–100	12×
Grade 5 / TC4	4.43	950	880	334 HB (36 HRC)	6.7	22%	30–60	18×

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Two patterns are worth reading off this table before you commit. Cost per kilogram misleads on light alloys: 7075 costs roughly three times 6061 per kilo, but at 2.81 g/cm³ against 316 stainless at 8.00 g/cm³, a 7075 part is often cheaper in absolute terms than the stainless equivalent despite the higher unit price. And thermal conductivity, not hardness, predicts tool life at the extremes. Grade 5 titanium is softer than hardened 440C yet runs slower, because 6.7 W/m·K leaves the heat in the cutting zone.

Grade Equivalents: ASTM, GB, JIS and EN

Our factories sit in Thailand and China, so drawings arrive in one standard and stock is bought in another. These are the cross-references we work to when a print calls out a grade by a different name.

Equivalents are nearest-match, not identical. Chemistry and permitted ranges differ slightly between standards, so where a specification is safety-critical we quote against the exact called-out grade rather than substituting.
Material	ASTM / AISI / UNS	GB (China)	JIS (Japan)	EN (Europe)
Aluminum	6061	6061 / 6A02	A6061	EN AW-6061, AlMg1SiCu
Aluminum	7075	7A09	A7075	EN AW-7075
Carbon steel	1045	45	S45C	C45E, 1.1191
Alloy steel	4140	42CrMo	SCM440	42CrMo4, 1.7225
Alloy steel	5140	40Cr	SCr440	41Cr4, 1.7035
Bearing steel	52100	GCr15	SUJ2	100Cr6, 1.3505
Stainless	304	06Cr19Ni10	SUS304	X5CrNi18-10, 1.4301
Stainless	316L	022Cr17Ni12Mo2	SUS316L	X2CrNiMo17-12-2, 1.4404
Stainless	17-4PH, S17400	05Cr17Ni4Cu4Nb	SUS630	X5CrNiCuNb16-4, 1.4542
Duplex	2205, S32205	022Cr23Ni5Mo3N	SUS329J3L	X2CrNiMoN22-5-3, 1.4462
Brass	C36000	HPb59-1	C3604	CuZn39Pb3, CW614N
Naval brass	C48500	HPb61-1	C4622	CuZn38Sn1Pb
Aluminum bronze	C63000	QAl10-4-4	C6301	CuAl10Ni5Fe4, CW307G
Titanium	Grade 2	TA2	Class 2	3.7035
Titanium	Grade 5, Ti-6Al-4V	TC4	Class 60	3.7165

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The substitutions that cause the most trouble are the near-misses. GB 45 steel carries a slightly wider carbon band than AISI 1045, and HPb59-1 runs a different lead content from C36000, which changes chip behaviour on long automatic turning runs. Where your print cites a standard we are not buying to, say so at quote stage and we will confirm the stock we intend to use.

Plastic Resin Property Matrix

Machined plastic has no shrinkage to design around, so the numbers that matter change. Thermal expansion and moisture uptake, not stiffness, decide whether a part is still in tolerance a week after it ships.

Typical unfilled virgin values at 23 °C. Glass and mineral filled compounds raise stiffness and service temperature while cutting thermal expansion by roughly half, at the cost of faster tool wear. Cost index is indicative stock cost per kilogram against ABS at 1.0×.
Resin	Density g/cm³	Tensile MPa	Cont. Service °C	Moisture 24h	Therm. Exp. µm/m·K	Held Tolerance	Cost Index
ABS	1.04	40	80	0.30%	90	±0.10 mm	1.0×
PC	1.20	65	115	0.15%	68	±0.08 mm	1.8×
PA6 (Nylon)	1.14	80	100	1.6–3.0%	85	±0.10 mm	1.6×
POM-C (Acetal)	1.41	70	100	0.20%	110	±0.03 mm	2.0×
PP	0.905	33	100	0.01%	150	±0.15 mm	0.9×
HDPE	0.95	26	80	<0.01%	200	±0.15 mm	0.9×
PEEK	1.32	100	250	0.10%	47	±0.03 mm	60–100×
TPU	1.20	35–55	80	0.3–0.8%	150	±0.20 mm	2.5×
UHMW-PE	0.93	40	80	<0.01%	200	±0.20 mm	1.4×

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Nylon is the grade that catches people out. At 1.6 to 3.0% moisture uptake it can grow enough across a 100 mm dimension to leave a part out of tolerance days after inspection passed, so a nylon part dimensioned to ±0.05 mm is not reliably deliverable unless it is sealed or dimensioned in the conditioned state. POM at 0.20% and PEEK at 0.10% behave far more predictably, which is why they carry the tightest held tolerances on this list despite POM having the highest thermal expansion of the two.

Choosing a Grade From the Numbers

Start with the constraint you cannot trade away, then read across the property matrix. One requirement usually eliminates most of the list before cost enters the discussion.

Two comparisons settle most decisions. 6061 against 7075: you are paying roughly 2.5× the stock price and dropping from 190% to 140% machinability to gain 85% more tensile strength, which is worth it for a load-bearing bracket and wasted on an enclosure. 303 against 316: 303 machines at 78% against 316 at 36%, meaning roughly double the cycle time for 316, so specify 316 only where the chloride exposure genuinely demands molybdenum.

At the extremes the numbers stop being linear. Moving from 316 stainless to 2507 super duplex costs you roughly 2× the stock price and takes machinability from 36% to 25%, but pitting resistance rises enough to matter in permanent seawater immersion where 316 will eventually fail.

Choosing a CNC machining material, aluminum, stainless steel and titanium bar stock compared

If Your Priority Is	Grade	The Number That Justifies It
Lowest cost, fastest turnaround	6061-T6	190% machinability at 1.0× cost and 300–900 m/min
Highest strength to weight	7075-T6	572 MPa at 2.81 g/cm³, a specific strength of 204 kN·m/kg
High volume turned fittings	12L14	170% machinability, the highest of any steel, at 0.9× cost
Machined stainless at lowest cost	303	78% machinability against 36% for 316, at 2.4× versus 3.2×
Chloride and sterilization resistance	316L	2–3% molybdenum; accept 36% machinability
Permanent saltwater immersion	2205 or 2507 duplex	450–550 MPa yield with PREN above 35
Marine hardware, machined detail	C48500 naval brass	210% machinability with dezincification resistance
Hardened wear surfaces	52100 / GCr15	60–64 HRC after heat treat; finish ground, not turned
Strength plus corrosion, heat treatable	17-4PH H900	1310 MPa tensile, the highest on this page
Low friction, unlubricated	POM-C or C93200 bronze	0.20% moisture uptake; ±0.03 mm held
Continuous service above 150 °C in plastic	PEEK	250 °C continuous, the only resin here that qualifies
Biocompatible, minimum weight	Titanium Grade 5	950 MPa at 4.43 g/cm³; 22% machinability is the price

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What Tolerance Each Material Actually Holds

A single blanket tolerance figure across all materials is a marketing number. Work hardening, thermal expansion, springback and moisture uptake mean the realistic figure differs by a factor of thirty from aluminum to TPU.

Tolerances are what we hold in a single production setup without special fixturing or a secondary operation, on features up to roughly 100 mm. Tighter is available on individual features, quoted case by case. Ra figures are as-machined without secondary finishing.
Material	Held Tolerance	Best Ra µm	Limiting Factor
Aluminum 6061, 6063	±0.010 mm	0.4	Thermal growth on long cuts; 23 µm/m·K expansion
Brass C36000	±0.010 mm	0.4	None significant; the easiest material here to hold
Free-cutting steel 12L14, 1215	±0.010 mm	0.8	None significant at production speeds
Carbon and alloy steel 1045, 4140	±0.013 mm	0.8	Tool pressure and workpiece deflection
Hardened 52100, 440C above 55 HRC	±0.005 mm	0.2 ground	Requires grinding; not achievable turned
Stainless 303	±0.013 mm	0.8	Mild work hardening
Stainless 304, 316	±0.015 mm	0.8	Work hardening and heat at 16 W/m·K
Duplex 2205, 2507	±0.020 mm	1.6	Severe work hardening, rapid tool wear
Titanium Grade 5	±0.020 mm	0.8	Elastic springback and heat at the tool tip
POM, PEEK	±0.030 mm	0.8	Thermal expansion four times that of steel
Nylon PA6	±0.100 mm	1.6	Moisture uptake shifts size after machining
PP, PE, UHMW, TPU	±0.150 to ±0.200 mm	3.2	Deflection under cutting force, creep under load

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If a drawing calls ±0.01 mm on a nylon part, the tolerance is not the binding problem — ambient humidity is, and the part will drift out of print regardless of how it was cut. Tell us the operating environment alongside the tolerance and we will say at DFM stage whether the combination is deliverable. For how tolerance classes are called out on a drawing, see how to choose CNC machining tolerances.

Material Questions the Tables Do Not Answer

Which material gives the lowest cost per finished part?

Not the cheapest stock. Finished cost is stock price × density × volume, plus cycle time driven by machinability. 1045 steel is cheaper per kilogram than 6061 at 0.8× against 1.0×, but at 7.85 g/cm³ against 2.70 and 57% machinability against 190%, the same part is usually cheaper in aluminum. Steel wins back the comparison only when the section is small and the part is turned rather than milled.

What does a machinability rating of 36% actually mean for my quote?

It is the percentage of the cutting speed that AISI B1112 free-cutting steel sustains at equal tool life. 316 stainless at 36% runs at roughly a third of that speed, so a feature taking one minute in B1112 takes close to three in 316, before allowing for extra tool changes. In practice, expect machining cost to scale inversely with the index and to add a further margin on grades below 40% for insert consumption.

Why is 316 so much more expensive to machine than 304 when the strength is identical?

Both list 515 MPa tensile, but the molybdenum in 316 raises the work-hardening rate and toughens the chip, dropping machinability from 45% to 36%. The practical consequence is roughly 25% more cycle time and noticeably shorter insert life. If the part does not see chlorides, 303 at 78% machinability does the same structural job for close to half the machining cost.

Which grades survive permanent saltwater immersion?

Duplex 2205 and super duplex 2507, naval brass C48500, and aluminum bronze C63000. The mechanism differs: the duplex grades resist chloride pitting through chromium, molybdenum and nitrogen, while C48500 resists dezincification through its tin addition. Standard 316 performs well in splash and washdown but will eventually pit under permanent immersion with stagnant flow. We machine C48500 into marine hardware including yacht lighting housings.

My drawing calls out GCr15 or 42CrMo. Can you work to a Chinese GB grade?

Yes, and we buy to GB directly rather than substituting. GCr15 is the GB bearing grade equivalent to AISI 52100, JIS SUJ2 and EN 100Cr6, reaching 60–64 HRC after heat treatment for bearing races and wear surfaces. 42CrMo maps to AISI 4140 and EN 42CrMo4. The full cross-reference is in the equivalents table above, and where the match is near rather than exact we confirm the intended stock at quote stage.

Can you hold the same tolerance in plastic as in metal?

No, and a supplier who says otherwise is quoting the machine rather than the material. POM and PEEK reach ±0.03 mm, nylon realistically ±0.10 mm because it absorbs up to 3% moisture after machining, and soft resins such as TPU and UHMW ±0.20 mm because they deflect away from the cutter. Metals reach ±0.010 to ±0.020 mm depending on work hardening and heat.

How to Get a Material Recommendation

Send the Drawing and the Operating Conditions

STEP or IGES plus a 2D drawing. Load, operating temperature, chemical or salt exposure, required finish and annual volume through the quote form.

Free DFM and Grade Review

We confirm the grade suits the geometry, flag tool access and thin wall issues, check the called-out tolerance is deliverable in that material, and say where a cheaper grade performs identically.

Quote in Under 24 Hours

Itemised piece price, the tolerance we will hold in that specific grade rather than a blanket figure, and one costed alternative where the trade is worth seeing.

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