Advantages and disadvantages of CNC milling machine

A CNC router is an intelligent manufacturing tool that produces 2D/3D engravings step-by-step by following tool paths created by CAD software through a computerised digital controller. No longer limited to basic prototyping, modern CNC routers can produce complex geometric shapes, with motion capabilities ranging from 3 to 5 axes, covering everything from woodworking to metalworking.

What are the main advantages of a CNC milling machine?

• High Precision and Accuracy

CNC milling machines offer extremely high mechanical and positioning accuracy, with machining precision of up to 0.01 mm, automatically milling CAD designs into high quality finished products without manual errors.

• High Repeatability

Once programmed, CNC routers can reproduce identical parts in batches, which is essential for mass production that meets quality standards.

• Increased productivity and speed

CNC routers can run faster and more continuously than hand-held routers, and can even run automatically around the clock. The automatic tool changer reduces downtime between operations and allows complex, multi-process tasks to be completed in a single setup.

• Complex geometries and intricate details

Ability to cut complex 2D, 2.5D and true 3D shapes that can't be made by hand or would take a lot of time to make by hand (e.g., intricate engraving, fine contours, 3D reliefs). Any fine work can be done with ease.

• Reduced labour costs and operator fatigue

Due to the complexity of manual work, the skills required of operators are lower than those required of master craftsmen (although programming still requires skilled labour). A lead operator can often easily manage multiple machines without the physical labour associated with manual routing.

• Versatility

CNC skeletonising machines can perform a variety of operations such as cutting, engraving, milling, drilling, slotting and chamfering. They can also handle a wide range of materials, from wood to metal, from foam to plastic, and even stone and ceramics (with the right cutter head).

• Enhanced safety

Throughout the machining process, the operator has minimal contact with the tool. Spindles and moving parts are usually enclosed. This reduces the risks associated with manual handling.

• Material optimisation and waste reduction

Automatic nesting software optimises the arrangement of parts on the raw material board, thus minimising waste and increasing utilisation. More accurate cutting means less unnecessary material loss compared to manual errors.

• Rapid Prototyping and Design Iteration

Easily and quickly turn CAD designs into physical prototypes for testing and evaluation. Simply modify the CAD file and cut the modified parts for a faster, more efficient design process.

• Scalability

Achieve scalable manufacturing from individual prototypes to small batches to high volume production by simply resubmitting the programme.

• Consistent quality

Every part produced according to the same programme has the same exact specifications, resulting in consistency throughout the production process.

• Integration with design workflow

Smooth integration with standard CAD (Computer Aided Design) and CAM (Computer Aided Manufacturing) software for a seamless digital process from design to finished product.

What are the main disadvantages of CNC milling machines?

Although a CNC milling machine can bring you many benefits, you must also be aware of its drawbacks. Below is an objective description of its main drawbacks:

• High initial investment

Most entry-level small CNC mills cost at least $2,000, while professional and industrial-grade CNC mills cost even more, ranging from $8,000 to more than $100,000 USD. There are also costs for software (CAD/CAM), tooling (drills), dust collection systems, workholding (jigs, vacuum pumps), and even equipment upgrades (power, space).

• Steep learning curve and high skill requirements

Programming (CAM): Developing error-free, optimised toolpaths is not easy and requires adequate CAD/CAM skills and experience, unlike operating a CNC milling machine. Operating and Setting Up: Setting up a CNC machine (such as tool selection and cutting parameter settings), defining workpiece offsets (especially in the Z-axis), and understanding how to troubleshoot require training, skills, and time. Maintenance: Understanding basic mechanical and electrical maintenance is critical to maximising uptime.

• Long setup and programming times

Not Always Instant: For one-off or small production runs, you may find that the time it takes to design (CAD)-programme (CAM)-tool/material setup and, in some cases, validate the programme, can be longer than the time it takes to get the part to the saw, mill or lathe for production. Complexity = Time: Whether it's a CAD design or part geometry, complex toolpaths require additional programming and machining time.

• High ongoing operating costs

Tools: Tools (end mills, routers) wear out and break. The cost of these tools is high and can be even higher when machining harder materials (metals and composites). Maintenance: Lubrication, calibration, belt and/or guideway replacement, spindle maintenance and repair are all operating costs. Power Consumption: Large industrial milling cutters consume a lot of power due to high torque and high speeds during heavy cutting. SOFTWARE UPDATES/SUBSCRIPTIONS: CAD/CAM software usually requires ongoing paid updates/subscriptions.

• Material wastage during learning and setup process

Trial and Error: Material is often wasted due to incorrect programming, setup, or tooling decisions that result in material damage, which is known as ‘scrap’. 

Fixture waste: Material is used only for workpiece fixtures (e.g., labels and scrap plates for vacuum attachment).

• Limited suitability for certain materials

Hard metals: Machining aluminium/brass is possible, but CNC routers are generally not suitable for efficient machining of hardened steel or heavy steel structures, so CNC milling/plasma cutting is more feasible. Hazardous materials: Machining other materials such as carbon fibre requires specialised or (expensive) dust collection equipment, as well as PPE for handling hazardous dust.

• Safety

High speed cutting: Splashing debris (chips, broken tools) is very hazardous and requires full enclosure and personal protective equipment (safety glasses, hearing protection). Dust inhalation: generates large amounts of fine dust (wood, plastics, composites, metals), requires effective dust collection systems. Moving parts/pinch points: Moving parts of automatic tool changers and shafts can cause tangling/pinch point problems during maintenance and installation phases. Noise: Routers can be extremely noisy.

• Space Allocation

MACHINE FOOTPRINT: Industrial routers have a large footprint and require space for operation and safe handling of construction materials and maintenance. Auxiliary Equipment: The machine requires auxiliary space for dust collectors, air compressors (vacuum pumps/ATCs are required), and material handling and storage equipment.

• Clamping Issues

It is difficult and time-consuming to safely and reliably clamp thin, flexible, irregularly shaped or small workpieces without deforming them. Vacuum clamping tables, while useful, have some limitations.

• Simple cuts aren't always faster

For simple cuts or openings in wood, it is faster for an experienced worker to use a hand-held milling or drilling machine than to write an operating programme and set it up on a CNC machine.

• Maintenance downtime

As mentioned in the downtime discussion, any electromechanical system is subject to failure. Whenever a malfunction or preventive maintenance results in downtime, the production schedule is affected.

• Risk of catastrophic failure

Programming errors (wrong Z-depth), tool damage, and fixture failures can lead to catastrophic damage to the machine spindle, bed, or fixture, which can be extremely costly.

• Considerations

CNC routers have had a disruptive impact on the manufacturing process. With unmatched repeatability, speed, accuracy and consistency, CNC routers can machine virtually any complex geometry. They can dramatically increase productivity, reduce labour and waste, enhance safety, and increase flexibility in materials and applications. While cost and skill requirements are important, CNC routers also offer certain economic benefits that make them invaluable in manufacturing, prototyping and custom production in today's market.

CNC routers are powerful manufacturing tools, but they are not a ‘magic bullet.’ Their main drawbacks are their high cost (initial purchase, operation, maintenance), the need for significant knowledge/expertise (programming, operation, maintenance), time-consuming (setup/programming), and safety/environmental concerns (dust, noise, airborne debris). They are usually limited to specific materials and the complexity of clamping/fixing techniques is limited.

Before making an investment, carefully weigh the pros and cons and weigh them against your unique needs (throughput, part complexity, materials, budget, available expertise). CNC routers are great for complex repetitive jobs, but for simple one-off jobs, a CNC router may be an overkill/unworkable solution.