CNC Material Machinability Chart

Q: What is IPR and how does it relate to IPM?

IPR stands for Inches Per Revolution, which is the feed rate per spindle revolution. IPM (Inches Per Minute) is the actual table feed rate. For turning: IPM = IPR x RPM. For milling: IPM = IPR per tooth x number of flutes x RPM. IPR is useful for comparing material recommendations because it is independent of spindle speed and tool diameter.

Material ▲	Grade / Alloy ▲	Machinability Rating (%) ▲	Cutting Speed SFM ▲	Feed Rate IPR ▲	Hardness ▲	Common Uses ▲
Aluminum	6061-T6	270	600 – 1000	0.004 – 0.010	95 HB	General purpose, brackets, housings, fixtures
Aluminum	7075-T6	240	500 – 900	0.004 – 0.008	150 HB	Aerospace structures, high-strength fittings
Aluminum	2024-T3	220	500 – 800	0.004 – 0.008	120 HB	Aerospace skins, fatigue-critical parts
Aluminum	6063-T5	280	600 – 1000	0.004 – 0.010	73 HB	Extrusions, architectural, heat sinks
Aluminum	5052-H32	200	500 – 800	0.004 – 0.008	60 HB	Marine, sheet metal, fuel tanks
Aluminum	2011-T3	310	700 – 1200	0.005 – 0.012	95 HB	Screw machine products, fittings
Aluminum	MIC-6 (Cast)	250	500 – 900	0.004 – 0.008	65 HB	Tooling plates, fixtures, base plates
Steel	1018 (Cold Rolled)	78	200 – 350	0.005 – 0.012	126 HB	Shafts, pins, general structural
Steel	1045 (Medium Carbon)	64	180 – 300	0.004 – 0.010	179 HB	Gears, shafts, bolts, studs
Steel	1215 (Free Machining)	136	300 – 500	0.005 – 0.015	167 HB	Screw machine products, high-volume parts
Steel	12L14 (Leaded)	170	350 – 550	0.006 – 0.015	163 HB	Precision turned parts, bushings, fittings
Steel	4140 (Pre-Hard)	66	150 – 275	0.004 – 0.008	28-32 HRC	Tooling, fixtures, high-strength components
Steel	4340 (Alloy)	57	130 – 250	0.003 – 0.007	30-36 HRC	Landing gear, crankshafts, heavy-duty parts
Steel	8620 (Case Hardening)	66	175 – 300	0.004 – 0.010	149 HB	Gears, camshafts, case-hardened parts
Steel	A36 (Structural)	72	180 – 325	0.005 – 0.012	119 HB	Structural plates, brackets, weldments
Steel	O1 Tool Steel	45	100 – 200	0.003 – 0.006	58-62 HRC (HT)	Dies, punches, cutting tools
Stainless Steel	303	78	200 – 350	0.004 – 0.010	170 HB	Free-machining fittings, shafts, valves
Stainless Steel	304	45	120 – 250	0.003 – 0.008	201 HB	Food equipment, medical, general purpose
Stainless Steel	316	36	100 – 220	0.003 – 0.007	217 HB	Marine, chemical processing, medical implants
Stainless Steel	17-4 PH (H900)	48	130 – 250	0.003 – 0.007	40 HRC	Aerospace, nuclear, high-strength valves
Stainless Steel	416	110	250 – 400	0.005 – 0.012	262 HB	Free-machining, valve stems, fasteners
Stainless Steel	440C	28	80 – 175	0.002 – 0.006	56-58 HRC (HT)	Bearings, knife blades, surgical tools
Titanium	Ti-6Al-4V (Grade 5)	22	60 – 120	0.003 – 0.006	36 HRC	Aerospace, medical implants, racing parts
Titanium	Grade 2 (CP)	40	100 – 200	0.003 – 0.008	80 HRB	Chemical processing, marine, medical
Titanium	Grade 5 ELI	20	50 – 110	0.002 – 0.005	36 HRC	Orthopedic implants, surgical devices
Titanium	Grade 23 (Ti-6Al-4V ELI)	20	50 – 110	0.002 – 0.005	36 HRC	Biomedical implants, aerospace fasteners
Plastic	Delrin (Acetal/POM)	350	500 – 1000	0.005 – 0.015	R120 (Rockwell M)	Gears, bearings, bushings, insulators
Plastic	PEEK	180	200 – 500	0.004 – 0.010	R126 (Rockwell M)	Aerospace seals, medical, semiconductor
Plastic	Nylon 6/6	300	400 – 800	0.005 – 0.012	R118 (Rockwell M)	Gears, rollers, bearings, wear pads
Plastic	UHMW-PE	320	400 – 900	0.005 – 0.015	R65 (Shore D)	Wear strips, conveyor guides, food handling
Plastic	Polycarbonate (PC)	280	400 – 800	0.004 – 0.010	R118 (Rockwell M)	Guards, lenses, transparent enclosures
Plastic	PTFE (Teflon)	250	300 – 700	0.004 – 0.012	R58 (Shore D)	Seals, gaskets, chemical-resistant parts

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Frequently Asked Questions

What does the machinability rating percentage mean?

The machinability rating is a relative measure based on AISI 1212 free-machining steel, which is rated at 100%. Materials above 100% are easier to machine, and materials below 100% are harder to machine. For example, 6061-T6 aluminum at 270% machines about 2.7 times as easily as 1212 steel. The rating accounts for tool life, surface finish, and cutting forces.

What is SFM and how do I use it?

SFM stands for Surface Feet per Minute. It is the speed at which the cutting edge of the tool moves across the material surface. To convert SFM to spindle RPM, use the formula: RPM = (SFM x 3.82) / tool diameter in inches. For example, machining 6061 aluminum at 800 SFM with a 0.5 inch end mill: RPM = (800 x 3.82) / 0.5 = 6,112 RPM.

Why is stainless steel harder to machine than carbon steel?

Stainless steel work-hardens during cutting, meaning the material gets harder as you machine it. It also has poor thermal conductivity, so heat builds up at the cutting edge. Additionally, stainless is gummy and tends to form built-up edge on the tool. Use sharp tools, positive rake angles, and consistent feed rates to avoid work hardening.

What is IPR and how does it relate to IPM?

IPR stands for Inches Per Revolution, the feed rate per spindle revolution. IPM (Inches Per Minute) is the actual table feed rate. For turning: IPM = IPR x RPM. For milling: IPM = feed per tooth x number of flutes x RPM. IPR is useful for comparing material recommendations because it is independent of spindle speed and tool diameter.

Can I machine titanium on a standard CNC mill?

Yes, but titanium requires a rigid machine setup, sharp carbide or coated tooling, and controlled cutting parameters. Titanium has low thermal conductivity, so heat stays in the cut zone. Use lower cutting speeds (60-120 SFM), maintain positive chip load to avoid rubbing, and use high-pressure coolant. Climb milling is preferred over conventional milling.

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