Which Machining Materials Chart Helps You Pick the Best CNC Material?
A machining materials chart should not just put alloys into tidy rows. It should help you check whether the material fits the part, the process, the tolerance, the surface finish, and the buyer’s budget. If you are comparing CNC materials for sourcing, prototyping, or production, keep this guide beside the Materials section and use it as a working reference, not as a hard rule.
Material choice can look easy when you only read the drawing. Then an M2 tapped hole breaks out, a thin stainless plate bends after roughing, or a titanium job burns through two end mills before lunch. That is why a usable chart needs both published data and shop experience. Public sources such as Sandvik Coromant’s workpiece material guide, the Metals Service Center Institute machinability rating table, ISCAR’s cutting tool guide, NIST material data resources, and ASM machining handbooks all point to the same point: the material name alone is not enough.
What Should a Machining Materials Chart Tell You?
A useful chart starts with the questions buyers and engineers ask before sending a drawing for quote. Can this material hold the tolerance? Will it rust or stain? Will it cut cleanly? Is the stock easy to buy in the needed size? A good chart puts these answers in one place, so you do not choose 304 stainless when 303 would reduce cycle time, or choose aluminum when the thread strength is not enough.
Material Family and ISO Cutting Group
Most cutting tool suppliers sort materials by family. Sandvik Coromant’s public workpiece material guide uses six main groups: P for steels, M for stainless steels, K for cast irons, N for non-ferrous metals, S for heat-resistant superalloys and titanium, and H for hardened materials. This helps because each family tends to damage tools in a different way. Steel often gives steady wear, stainless can work harden, and titanium keeps much of the heat close to the cutting edge.
Machinability Rating and Shop Behavior
Machinability ratings give a quick idea of how a material cuts compared with a reference steel. The Metals Service Center Institute states that its ratings are based on AISI 1212 cold drawn bar at 100 percent. A higher number usually means easier cutting, cleaner chip control, and less tool wear. Even so, the number is only a guide because a small desktop mill and a rigid turning center will not cut the same bar in the same way.
Strength, Heat, and Corrosion Limits
A chart also needs basic notes on mechanical properties and service conditions. Tensile strength, hardness, thermal conductivity, and corrosion resistance affect both machining cost and part life. NIST material data programs and ASM references are useful background sources for these properties. The final choice still needs to match the material certificate, the drawing standard, and the buyer’s real application.
Which Metals Machine Fastest for CNC Parts?
If speed and cost are the main concerns, start with metals that cut cleanly and are available in common bar, plate, or extrusion sizes. Fast machining usually means shorter cycle time, easier burr control, and fewer tool changes. It also makes quoting more straightforward. Most buyers do not want to pay aerospace titanium prices for a simple bracket that could be made from aluminum.
Aluminum 6061 for Quick Prototypes
Aluminum 6061 is one of the safer first choices for CNC prototypes, fixtures, brackets, housings, and test parts. It cuts fast, anodizes well, and gives fair strength for its weight. ASM Handbook machining references treat aluminum alloys as an important machinable family, and NIST’s structural material data work has included 6061 alloy data because it is used so often. For many jobs, 6061 gives a good balance of speed, cost, and stock availability.
Free-Machining Steel for Screw-Machine Work
Free-machining steels such as 1212 or 12L14 are made for high-volume cutting. Sulfur, lead, or similar additions help the chip break and reduce tool load. In machinability charts, these grades often rank high because the reference material itself is a free-machining steel. The tradeoff is simple: you get better cutting speed, but you may give up weldability, toughness, or use in some controlled applications.
Brass and Copper When Chips Behave
Brass is often easy to run for small turned parts, fittings, electrical pins, and decorative components. Chips break well, edges stay clean, and cycle time can be short. Copper is not the same story. It has strong electrical and thermal performance, but pure copper can feel sticky in the cut, so it is worth asking whether a certain copper alloy can improve machining without hurting the electrical target too much.
Which Materials Cause the Most Machining Risk?
Hard-to-machine does not mean the material is wrong. It means the quote should allow for slower cutting, stronger workholding, better coolant delivery, and more inspection time. Many high-spec parts need stainless steel, titanium, hardened steel, or nickel alloy. The problem starts when someone treats them like easy aluminum and expects the same price and lead time.
Austenitic Stainless Steel Work Hardening
Stainless steels such as 304 and 316 resist corrosion, but they can work harden if the tool rubs instead of cutting. Public supplier data often rates 303 stainless around 78 percent compared with a free-machining reference, while 304 and 316 are commonly listed much lower in cold drawn bar charts, often around the mid-40 percent range. That gap matters in real production. If the corrosion requirement allows it, 303 can cut cleaner than 304 for shafts, spacers, and threaded fittings.
Titanium Heat Staying Near the Tool Edge
Titanium Grade 5, also called Ti-6Al-4V, is strong and light, but it does not forgive poor process planning. A 2023 peer-reviewed review available through PubMed Central reported that Ti-6Al-4V is commonly machined at cutting speeds below 90 m/min, while aluminum machining can reach much higher speeds in some cases, even up to 2500 m/min under suitable conditions. The reason is easy to understand from the shop side. Titanium does not conduct heat well, so heat stays near the tool and the cutting edge wears quickly.
Hardened Steel and Nickel Alloy Tool Wear
Hardened steels and nickel alloys bring another kind of machining trouble. They may resist deformation, keep strength at high temperature, or survive corrosive service, but they can push cutting force and tool wear up quickly. ISCAR’s public cutting tool guide lists annealed Ti-6Al-4V at a low machinability value compared with free-cutting steel, and superalloy charts often fall into the same difficult range. For these materials, quote time should include trial cuts when the tolerance stack is tight.
How Should You Read Machinability Ratings?
Machinability numbers are useful only when you know what they are comparing. One chart may use AISI 1212 as 100. Another may use B1112 or a different test condition. The rating can also come from turning tests, tool life, or speed at a set wear limit. So the number helps, but it should not override the drawing, the machine, or the cutter supplier’s current data.
Do Not Mix Rating Systems
If one table says 1018 steel is 78 percent of B1112, and another table bases values on 1212 cold drawn bar, those numbers are not fully interchangeable. AZoM’s public material page for AISI 1018, for example, describes machinability against B1112, while MSCI explains a 1212 basis for its rating table. Use ratings to compare materials inside the same chart first. After that, check the actual tool data before locking the process.
Treat 100 Percent as a Reference
The 100 percent number does not mean the material is perfect. It only means the reference cut was assigned that value. A material rated 50 percent may need lower speed, different tooling, or closer chip control. It can still be the right material if the part needs it, such as a food-contact component that requires 316 stainless. See also: Machines.
Use Ratings to Start, Not to Finish
Use the chart to choose a starting point, then confirm it with tool maker data, part geometry, and first-article feedback. Thin walls, deep pockets, cross holes, interrupted cuts, and tiny taps can all change the result. A 20 mm thick plate is not the same job as a 1.2 mm wall, even if both are 6061 aluminum. This is where early supplier discussion can prevent rework.
How Do Plastics Fit the Chart?
Plastics need their own place in a machining materials chart because they do not fail like metals. They may move with heat, absorb moisture, creep under load, or make long stringy chips. They can also solve problems that metal makes worse, such as weight, electrical insulation, sliding wear, or chemical exposure.
Acetal for Stable Precision Parts
Acetal, often sold under common trade names, is a practical choice for gears, rollers, bushings, and small precision parts. It machines cleanly and holds size better than many general plastics. If you need a plastic that behaves well on a CNC mill, acetal is usually near the top of the list. It is also easier to quote than many specialty plastics because stock is common.
Nylon for Wear Parts With Moisture Notes
Nylon works well for wear pads, wheels, guides, and impact parts. It is tough and useful, but it can absorb moisture and change size. That small point matters for close tolerance holes or press fits. If the part will run outdoors or near water, put a moisture note into the material review before ordering stock.
PTFE and PEEK for Special Conditions
PTFE gives low friction and strong chemical resistance, but it is soft and can deform under clamping. PEEK costs much more, but it can handle heat, strength, and harsh service better than many plastics. For both materials, the chart should remind you to check cost, clamping pressure, burr control, and realistic tolerance limits. These parts often need a slower, more careful setup than the drawing first suggests.
How Can You Choose a Material for Your Part?
The right choice usually comes from narrowing the list, not from picking the strongest material on the page. Start with what the part must do in service. Then remove materials that fail on cost, lead time, corrosion, temperature, weight, tolerance, or surface finish. This simple filter saves time and helps suppliers quote with fewer assumptions.
Start With Function and Failure Mode
Ask what would make the part fail in use. It could be wear, bending, rust, heat, a cracked thread, or a visible scratch. A bracket may only need 6061 aluminum, while a shaft might need 4140 steel. A marine fitting may need 316 stainless or bronze, and a medical or aerospace part may require a controlled alloy, full traceability, and a certificate.
Match the Material to the Machine Route
Turning, milling, wire EDM, grinding, and sheet machining all prefer different material behavior. A round bushing in 303 stainless may be easy on a lathe, but the same alloy in a thin milled plate may still move after roughing. For tight flatness, plan roughing, stress relief if needed, and finishing cuts on both sides. This planning should happen before the purchase order, not after the first parts are rejected.
Ask for a Material Certificate When It Matters
For prototypes, common commercial stock may be enough. For production, safety, export, or regulated parts, ask for grade, standard, heat lot, and certificate data. Charts help you choose a direction, but certificates prove what was supplied. When reliable public data is not available for a niche alloy or filled plastic, it is safer to request supplier documentation instead of guessing.
FAQ
Q1: What Is a Machining Materials Chart? A: It is a comparison guide that shows how common metals and plastics behave during CNC machining, including machinability, strength, corrosion resistance, cost, and typical use cases.
Q2: Which CNC Material Is Easiest to Machine? A: Aluminum 6061, free-machining brass, and free-machining steels are usually among the easiest common choices. The exact answer depends on part shape, machine rigidity, tool type, and tolerance.
Q3: Is 303 Stainless Better Than 304 for Machining? A: For cutting speed and chip control, 303 is usually better because it is a free-machining stainless grade. For welding and some corrosion needs, 304 may be the better choice.
Q4: Why Is Titanium Expensive to Machine? A: Titanium keeps heat near the cutting edge, needs slower speeds, and can wear tools quickly. The raw stock also costs more than common aluminum or carbon steel.
Q5: Should You Choose the Strongest Material Available? A: Not always. The best material is the one that meets the load, environment, tolerance, finish, lead time, and cost target without adding needless machining risk.
