The Xometry app works best with JavaScript enabled!
Xometry Logo
Sign In
Search
CapabilitiesIndustriesResourcesSuppliesBecome a Supplier
Search
Machining Services
Materials
Finishes
Design Guidelines
CNC FAQs
Applications
Customer Examples

What is CNC Machining?

CNC (computer numerical controlled) machining is a widely used manufacturing process that uses automated, high-speed cutting tools to form designs from metal or plastic stock. Standard CNC machines include 3-axis, 4-axis, and 5-axis milling machines, lathes, and routers. Machines may vary in how parts are cut—the workpiece may remain in place while the tool moves, the tool may remain in place while the workpiece is rotated and moved, or both the cutting tool and workpiece may move together. 


Skilled machinists operate CNC machines by programming tool paths based on the geometry of the final part. The part geometry information is provided by a CAD (computer-aided design) model. CNC machines can cut almost any metal alloy and rigid plastic with high precision and repeatability, making CNC machined parts suitable for nearly every industry, including aerospace, medical, robotics, electronics, and industrial. Xometry offers CNC machining quotes on over 40 materials ranging from commodity aluminum and acetal to advanced titanium and engineered plastics like PEEK and Teflon.

    CNC Turning Machine Image

    Why Use Xometry for Custom CNC Machining Services?

    Xometry provides custom CNC machining services to engineers, product developers, designers, and more through our vetted network of 5,000+ suppliers. Our highly qualified ASD9100 machine shops can make any custom design, simple or complex. We offer rapid CNC prototypes, small-batch machining, and high-volume production, with all orders serviced by Xometry from end to end. Upload a CAD file to the Xometry Instant Quoting Engine℠ to get a price, lead time, and design-for-manufacturability feedback on your custom CNC parts. Our CNC service offers metals and plastics and flexible production and shipping options to meet you at the perfect price and product development stage. 


    Xometry guarantees the quality of your parts with our ISO 9001:2015 and AS9100D certified quality management system, ITAR registration, and options to add inspections, hardware traceability, material certifications, and CoCs. We accept technical drawings and have support teams to ensure you get your CNC machined parts at quality and on time.

    CNC machined part, round part image

    CNC Services: Machining, Turning, and Milling

    CNC milling machine machining part

    CNC Milling Service

    CNC Milled Prototypes and Production Parts in as Fast as 1 Day | AS9100D | ISO9001:2015 | ITAR Registered | Free Standard Shipping on All US Orders

    CNC Milling Service
    CNC turning occurring

    CNC Turning Service

    CNC Turned Prototypes and Production Parts in as Fast as 1 Day | AS9100D | ISO9001:2015 | ITAR Registered | Free Standard Shipping on All US Orders

    CNC Turning Service
    CNC Machining Tolerances
    FeatureDescription
    Feature

    Maximum Part Size

    Description

    Milled parts up to 80” x 48” x 24” (2,032 x 1,219 x 610 mm). Lathe parts up to 62” (1,575 mm) length and 32” (813 mm) diameter.

    Feature

    Standard Lead Time

    Description

    3 business days

    Feature

    General Tolerances

    Description

    Tolerances on metals will be held to +/- 0.005" (+/- 0.127 mm) in accordance with ISO 2768 unless otherwise specified. Plastics and composites will be +/- 0.010”.

    Feature

    Precision Tolerances

    Description

    Xometry can manufacture and inspect to tight tolerances per your drawing specifications including GD&T callouts.

    Feature

    Minimum Feature Size

    Description

    0.020” (0.50 mm). This may vary depending on part geometry and chosen material.

    Feature

    Threads and Tapped Holes

    Description

    Xometry can accommodate any standard thread size. We can also machine custom threads; these will require a manual quote review.

    Feature

    Edge Condition

    Description

    Sharp edges are broken and deburred by default

    Feature

    Surface Finish

    Description

    The standard finish is as-machined: 125 Ra or better. Additional finishing options can be specified when getting a quote.

    This table depicts the general tolerances for CNC machining. Learn more about our manufacturing standards.

    Metal CNC Machining Materials
    CNC Machining Aluminum Alloys

    Aluminum 6061

    Aluminum 5052

    Aluminum 2024

    Aluminum 6063

    Aluminum 7050

    Aluminum 7075

    Aluminum MIC-6

    Learn more about aluminum for CNC machining.


    CNC Machining Copper Alloys

    Copper 101

    Copper C110

    Learn more about copper for CNC machining.

    CNC Machining Bronze Alloys

    Copper C932

    Learn more about bronze for CNC machining.

    CNC Machining Brass Alloys

    Copper 260

    Copper 360

    Learn more about brass for CNC machining.

    CNC Machining Stainless Steel Alloys

    Nitronic 60 (218 SS)

    Stainless Steel 15-5

    Stainless Steel 17-4

    Stainless Steel 18-8

    Stainless Steel 303

    Stainless Steel 316/316L

    Stainless Steel 416

    Stainless Steel 410

    Stainless Steel 420

    Stainless Steel 440C

    Learn more about stainless steel for CNC machining.

    CNC Machining Steel Alloys

    Steel 1018

    Steel 1215

    Steel 4130

    Steel 4140

    Steel 4140PH

    Steel 4340

    Steel A36

    Learn more about steel for CNC machining.

    CNC Machining Titanium Alloys

    Titanium (Grade 2)

    Titanium (Grade 5)

    Learn more about titanium for CNC machining.

    CNC Machining Zinc Alloys

    Zinc Alloy

    Learn more about zinc for CNC machining.

    Custom

    We can source additional alloys and tempers from within our network of 5,000 machine shops. If you do not see the material stock you are looking for, please choose "Custom" under the material drop-down in the Xometry Instant Quoting Engine℠. You can then submit your quote for manual review and our expert manufacturing team will reach out.

    Plastic CNC Machining Materials
    ABS

    High-strength engineering plastic used for many commercial products.

    Learn more about ABS for CNC machining.

    Acrylic

    A clear glass-like plastic. Good wear and tear properties. Great for outdoor use.

    Learn more about acrylic for CNC machining.

    Delrin (Acetal)

    Resin with good moisture resistance, high wear-resistance, and low friction.

    Learn more about Delrin for CNC machining.

    Garolite G10

    Constructed of an epoxy resin with fiberglass fabric reinforcement, and also called epoxy-grade industrial laminate and phenolic, this material offers high strength and low moisture absorption.

    Learn more about garolite G10 for CNC machining.

    HDPE

    High-density polyethylene is a moisture and chemical-resistant plastic with good impact strength. The material is outstanding for outdoor applications as well as watertight containers or seals.

    Learn more about HDPE for CNC machining.

    Nylon 6/6

    Offers increased mechanical strength, rigidity, good stability under heat and/or chemical resistance.

    Learn more about Nylon 6/6 for CNC machining.

    PC (Polycarbonate)

    With almost twice the tensile strength of ABS, polycarbonate has superior mechanical and structural properties. Used widely in automotive, aerospace, and other applications that require durability and stability.

    Learn more about PC for CNC machining.

    PEEK

    Offering excellent tensile strength, PEEK is often used as a lightweight substitute for metal parts in high-temperature, high-stress applications. PEEK resists chemicals, wear, and moisture.

    Learn more about PEEK for CNC machining.

    Polypropylene

    Has excellent electrical properties and little or no moisture absorption. It carries light loads for a long period in widely varying temperatures. It can be machined into parts requiring chemical or corrosion resistance.

    Learn more about polypropylene for CNC machining.

    PTFE (Teflon)

    This material surpasses most plastics when it comes to chemical resistance and performance in extreme temperatures. It resists most solvents and is an excellent electrical insulator.

    Learn more about PTFE for CNC machining.

    UHMW PE

    Ultra-high molecular weight polyethylene. A general-purpose material. It offers a unique combination of wear and corrosion resistance, low surface friction, high impact strength, high chemical resistance, and does not absorb moisture.

    Learn more about UHMW-PE for CNC machining.

    PVC

    Polyvinyl chloride (Type 1) is a highly chemical-resistant synthetic plastic, PVC is commonly in environments exposed to liquids or requires electrical insulation.

    Learn more about PVC for CNC machining.

    Custom

    We can source additional CNC machining plastics from within our network of 5,000 machine shops. If you do not see the material stock you are looking for, please choose "Custom" under the material drop-down in the Xometry Instant Quoting Engine℠. You can then submit your quote for manual review and our expert manufacturing team will reach out.

    Slide 1 of 4
    • CNC Part closeup image

    CNC Threads

    CNC Machining Finishes
    Standard (As-Milled)

    The finish option with the quickest turnaround. Parts are left with visible tool marks and potentially sharp edges and burrs, which can be removed upon request. Surface finish is comparable to 125 uin Ra finish.

    Bead Blast

    The part surface is left with a smooth, matte appearance.

    Tumbled

    This is a batch-based process that tumbles vibrating media to remove sharp edges and burrs on machined parts. Tumbling can remove machine marks on exterior surfaces. Parts over 8” may require a manual review.

    Anodized (Type II Or Type III)

    Type II  (MIL-A-8625, Type II) creates a corrosion-resistant finish. Parts can be anodized in different colors—clear, black, red, and gold are most common—and is usually associated with aluminum. Type III (MIL-A-8625, Type III, Class 1/2 "hardcoat") is thicker and creates a wear-resistant layer in addition to the corrosion resistance seen with Type II.

    Titanium Anodize

    A surface finish for titanium per AMS-2488 Type 2 specification. Also called Tiodize, this finish increases fatigue strength and the wear resistance of a part. Titanium anodized parts are common in aerospace and medical device manufacturing. Non-pigmented titanium anodize finishes will dull shine.

    PTFE Impregnated Hard Anodize

    A hard coat anodize process that embeds PTFE to create a self-lubricating, dry contact surface with Type 3 hard coat’s protective properties. This finish can be used on aluminum alloys or titanium and increases the service life of the product. This finish conforms to the AMS-2482 Type 1 Hard Coat Anodizing with Teflon (Non-Dyed).

    Chem Film (Chromate Conversion Coating)

    Provides corrosion resistance and good conductivity properties. Can be used as a base for paint. Can leave surface yellow/gold. Adds very little thickness, about 0.00001”-0.00004”. Chem film will conform to MIL-DTL-5541, TYPE I/II.

    Passivation

    Improves corrosion resistance for 200 and 300 series and precipitation hardened corrosion-resistant steels. Thickness is negligible, about 0.0000001”. Conforms to ASTM A967, AMS-QQ-P-35, MIL-STD-171, ASTM A380, or AMS 2700.

    Powder Coat

    This is a process where powdered paint is sprayed onto a part that is then baked in an oven. This creates a strong, wear- and corrosion-resistant layer that is more durable than standard painting methods. A wide variety of colors are available to create the desired aesthetic.

    Electropolishing

    An electrochemical process cleans steel parts to reduce corrosion and improve appearance, by making the metal brighter. Removes about 0.0001”-0.0025” of the metal. Conforms to ASTM B912-02.

    Electroless Nickel Plating

    Provides uniform nickel coating which offers protection from corrosion, oxidation, and wear on irregular surfaces. The finished part will be brighter. Thickness starts at .0001”. Conforms to MIL-C-26074.

    Silver Plating

    Silver offers high solderability and electrical conductivity but is susceptible to tarnish. Conforms to AMS QQ-S-365D. Thickness is about 0.00002” - 0.0003.”

    Gold Plating

    Gold Plating provides good corrosion and tarnish resistance with excellent solderability. Default application specification is MIL-G-45204 and ASTM B488, CLASS 00, 0, OR 1. Thickness is about 0.00002" - 0.00005."

    Zinc Plating

    Provides uniform zinc coating which offers protection from corrosion, oxidation, and wear on irregular surfaces. Conforms to ASTM B633-15.

    CNC Machining Design Guidelines
    FeatureDescription
    Feature

    Internal corner fillets

    Description

    Design internal corner fillets to be 0.020” - 0.050” greater than a standard drill size for the radii. Follow a drill diameter to depth ratio of 1:6 (1:4 recommended) as a guideline for internal corner radii.

    Feature

    Floor fillets

    Description

    Design floor fillets smaller than corner fillets to allow the same tool to clear material from the interior.

    Feature

    Undercuts

    Description

    Always design undercuts to standard sizes and away from corners so they are accessible by the cutting tool.

    Feature

    Tapped/threaded hole depth

    Description

    Provide tool clearance slightly beyond the tapped hole depth to ensure complete threads.

    Feature

    Complexity

    Description

    Keep the number of small cuts to a minimum to reduce costs; only design in the necessary features to balance function with aesthetic.

    To see more design-for-manufacturing recommendations, view our CNC Machining Design Guide.

    CNC Machining FAQs
    How does CNC machining work?

    CNC machining uses subtractive processes, which means feedstock is machined to its final form by subtracting and removing material. Holes are drilled, lots and pathways are bored, and metal stock is shaped into new material with varying tapers, diameters, and shapes.


    For subtractive manufacturing, shapes are achieved by the subtraction of material. This contrasts with other types such as additive manufacturing — where materials are added, layered, and deformed to a specified shape. It also contrasts with injection molding where the material is injected in a different state of matter, using a mold, and formed to a specified shape.


    CNC machining is versatile — and can be used with various materials, including metals, plastics, wood, glass, foam, and other composite materials. This versatility has helped make CNC machining a popular choice across industries, enabling designers and engineers to fabricate products efficiently and precisely.

    How does CNC machining differ from traditional machining?

    In traditional machining, a skilled machinist operates a machine, removing or forming metal. This is done according to specifications provided by designers and engineers, usually through an engineering drawing or blueprint. They use turn wheels, dials, switches, chucks, vices, and a variety of cutting tools made of hardened steel, carbide, and industrial diamond, then use measurement instruments to ensure all of the dimensions are correct.


    CNC machining performs the same function as traditional machining — metal cutting, drilling, milling, boring, grinding, and other metal forming and removal functions — but it uses computer numerical control rather than manual control by a machinist. It is automated, driven by code, and developed by programmers. It is about as precise the first time of cutting as the 500th. Widely used in digital manufacturing (and sometimes in low-volume production runs), it can be revised and altered for modifications and different materials.


    This type of machining is much more precise and has superseded traditional machining (though not entirely) in manufacturing, fabrication, and industrial production. It uses mathematical coordinates and computing power to achieve the same end with the greatest accuracy. Specifically, computer numerical control uses Cartesian coordinates. These are spatial coordinates — in several dimensions — using coordinates and axes. The automation of cutting tool machines controls its cutting, boring, drilling, or other operation using the numerical control of a computer that reads the coordinates. These coordinates were designated by engineers in the product’s digital drawing and design.

    What industries use CNC machining?

    CNC machining is widely used across industries. It is common in aerospace, automotive, consumer electronics, robotics, agriculture, and other fields that frequently use metal parts. It is also widely used in medical devices, household goods, energy, oil and gas, and other consumer applications. It is one of the most common manufacturing processes in the world.

    What is the history of CNC machining?

    During World War II, the United States was quickly churning out ships, aircraft, and vehicles for the military. And even once the war ended, production kept up as the country experienced a post-war boom in home construction, infrastructure expansion, and transportation. Naturally, engineers and designers needed tools to help them efficiently meet the growing demand for industrial products.


    Enter CNC machining. John T. Parsons, who worked in the production of helicopter rotor blades, was one of the first people to champion CNC machining. He and his colleagues at Wright-Patterson Air Force Base in Dayton, Ohio used interpolation curves, which could be applied to machining with computational methods, to achieve the complex tapers required for rotor blades. As Parsons’ company got called upon to make more and more complex aircraft parts, they turned to computational methods to achieve their desired shapes.


    This was partly the genesis of CNC machining. Building off of Parsons’ innovations, MIT’s Servomechanisms Laboratory later developed a working machine able to use computational methods to fabricate precise machine parts. Their servo-mechanisms were able to use the Cartesian coordinates — the numerical control — to steer the machine and its moving parts, to fabricate with automated precision. Such automation only grew more sophisticated through the rest of the twentieth century and continues to develop today.

    What are your inspection options for CNC machining?

    We offer (6) different inspection options on the Modify Parts window under the Inspection tab in the quoting platform. All machined and sheet metal parts will receive a standard inspection included in the part price and lead time. See more on our inspections and sampling.

    What are your tolerances for machined parts?
    • +.005”/-.005” local tolerances across most geometries in metals, +/- 0.010" for plastics.  Will vary for large parts, specifically when holding flatness over large parts after heat treatment. 
    • Finish requirements for “As Milled” finish will have a minimum 125 surface finish for CNC parts.
    • All fabricated parts have a 0.010” dimensional and 1° angular tolerance.
    • Tapped holes not explicitly called out as Features on the quoted CAD model may be machined to the diameters specified in that model.
    • No surface treatments (e.g. anodize, bead blast, iridite, powder coat, etc.) will be applied unless you have paid for them and we have specifically acknowledged them.
    What are your CNC machining & turning capabilities?

    Xometry has significant capabilities in machining through our shop services and the Manufacturing Partner Network. In general, here are some guidelines for machine size but if you do have a quote that pushes to RFQ please make sure to request a quote review so we can take a look!

    ‣ 5 Axis Machining up to 26″
    ‣ 4 Axis Machining up to 36″
    ‣ 3 Axis Machining up to 60″
    ‣ Dual Spindle Lathes with 32″ Swing, 18″ Max Diameter, and 8″ Chuck
    ‣ Wire EDM with a part depth of 18″

    Advantages and Challenges of CNC Machining

    CNC Machining Threaded Hole
    Advantages of CNC Machining
    CNC Machining Threaded Hole

    CNC milling and turning are highly accurate and repeatable processes. Tight tolerances between +/-0.001″ – 0.005″ can be achieved, depending on specifications. Machines can be programmed to reliably run for 24 hours, 7 days a week if necessary, so CNC milling is a good way of getting parts produced on demand.


    Using standard tooling, CNC machining is particularly valuable for creating custom, one-off parts, i.e., for replacing legacy components or delivering a specialized upgrade to a customer. It is also conceivable to scale single-part production to runs exceeding 10,000 units. Depending on the unit number, size, and complexity, the turnaround for components can be as short as one day. With shipping and delivery, deadlines can be met within a week.


    Another primary advantage of CNC technology is its achievable mechanical properties. By cutting away from bulk material, rather than thermally transforming it as in injection-molding or additive manufacturing, all desirable mechanical properties of the metal or plastic of choice are retained. More than 50 industrial-grade metals, alloys, and plastics can be machined using CNC milling and turning. This selection includes aluminum, brass, bronze, titanium, stainless steel, PEEK, ABS, and zinc. The only material requirement for CNC machining is that the part has an adequate hardness to be fixtured and cut.

    Challenges of CNC Machining
    CNC Machined Part

    One trade-off when taking advantage of the high performance of CNC machining is that geometric complexity comes at a cost. Simple, chunky parts are the best designs for CNC milling and turning. There will always be some design limitations due to tool access, although the degree of this effect is relative to the number of axes on the machine. In other words, the more axes used, the more complex the features can be achieved.

    Another trade-off is that start-up costs for CNC machining can be expensive. It is necessary to have a trained professional perform the setup, tool loading, and programming on CNC mills and lathes. Luckily this cost is fixed, so by taking advantage of the same setup for multiple parts, it becomes more economical. Saving money is also achieved by keeping part repositioning to a minimum. Machining at 5-axis and above can sometimes be more economical on multi-faceted geometries because it eliminates the need to manually reposition the part.


    The wire EDM method of machining can be slow and expensive relative to other processes, and the range of materials that can be used is shortened as they must be electrically conductive.

    CNC Machining Applications

    CNC machined threaded holes

    Rapid Tooling

    Because CNC machining can cut a high variety of fully dense, durable materials like aluminum 5052 and stainless steel, it is perfect for creating fixtures or molds.

    CNC machining - gear

    Rapid Prototyping

    The range of affordable metal alloys (like aluminum 6061) and plastics (like acetal or ABS) combined with the speed of our skilled machinists makes our CNC service a great option for prototyping.

    CNC Machining Services

    End-Use Production

    Performance-enhancing finishes, precision tolerances as low as +/- 0.001”, and certifiable material options make CNC machining an excellent technology for end-use parts.

    CNC machining services at Xometry

    Ready to Get a CNC Machining Quote?

    Examples of Our CNC Machining Work

    Article
    BattleBots Team HyperShock Prepares to Dominate the Battle Arena With Purpose-Built Xometry Parts
    By Serena Ngoh
      5 min read
    Video
    Video: NASA Partners with Xometry to Fast-track Critical Life Support Systems on the ISS
    By Serena Ngoh
    Article
    Case Study: Xometry Helps Zaiput Build Flow Technology for the Global Pharmaceutical Industry
    By Serena Ngoh
      4 min read
    Article
    Case Study: Cal Poly Hyperloop Team SLOs Down with Xometry Brakes
    By Serena Ngoh
      5 min read

    Ready to Get Your Project Started?

    Additional CNC Machining Resources
    How to Reduce CNC Machining CostsCNC Tolerances GuideCNC Lathe ServiceCNC Parts With Undercuts5 Axis MachiningCNC Machining LocationsChoosing Finish for CNC PartsChoosing an Online Machine Shop