CNC vs 3D Printing: Which is best for Prototyping?

CNC vs 3D Printing: Which is best for Prototyping?

CNC vs 3D Printing: Which is best for Prototyping?

3D printing and CNC machining are more popular and accessible than ever.

When you're looking to make a prototype, how do you decide which one to go with?

In this article, I show you the strengths and weaknesses of each technology to help you come to a decision.

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Difference Between 3D Printing and CNC Machining

The difference between 3D printing and CNC machining is that 3D printing is additive manufacturing while CNC is subtractive manufacturing. 3D printers have a nozzle that delivers layers of material to produce the parts, whereas CNC machining consists of a cutting tool that removes material to produce the parts.

CNC machines provide the ability to replace the cutting tool to match the intricacy of the application. As a result, CNC machines can be used for producing comparatively more detailed products, with high accuracy.

On the other hand, 3D printers are capable of producing complex shapes, making them ideal for rapid prototyping applications.

But is a 3D printer a CNC machine? The short answer is yes, it is a type of CNC machine that consists of a computer-controlled nozzle to print the material.

However, 3D printing involves heating of the work element, followed by cooling and solidification. This increases the overall machining time required for producing an object.

Apart from this, there are various other differences that differentiate a 3D printer from a CNC machine.

Workflow

When looking at CNC machines and 3D printers from a technical point of view, both these machines are computer controlled.

Interestingly, 3D printers come under the additive manufacturing branch of CNC machines.

types of CNC machines
3D printers are a type of CNC machine

The motion control system on CNCs is responsible for moving the cutting head across the material.

In 3D printers, the cutting head is replaced by a printing head that deposits the material while the controller governs its movement to print the desired shape or object.

Like any other CNC machine, 3D printers also have a similar workflow. The differences arise in the manufacturing process.

A typical workflow of CNC machines and 3D printers includes:

  • Designing the part model on CAD software,
  • Producing toolpath for the CAD design using CAM software
  • Checking the program file for any errors using simulation software
  • Correcting errors in the design or toolpath.
  • Machining or printing the part.

CNC machines use CAD/CAM software to create designs and G-code files that are programmed into the machine for manufacturing.

Most 3D printing applications only require a 3D design file of the part to be printed. It then uses slicing software to generate the part program from the design.

The slicing software used with 3D printers is similar to the CAM software used with CNC machines. They both generate the G-code file used by CNC controllers.

Material Wastage

CNC Metal Milling with air assist
CNC Metal Milling

Material wastage in 3D printing is lower than that of CNC machining. The main reason is that 3D printers only use the needed material to create a part.

Since CNCs use the subtractive manufacturing technique, they continuously cut and sculpt a block of material to make out the desired shape, and this causes a lot of material wastage.

Size and Build

Compared to 3D printers, CNC machines are readily available in larger sizes. Making 3D printers more portable than CNC machines.

Most XXL-rated CNCs have a work area of a few square meters, while large 3D printers can have a maximum work area of 1 square meter.

For example, some of the giant 3D printing machines have a build volume similar to 1500 × 1200 mm. While most industrial-grade CNCs can have a work area of 3,500 X 10,000 mm and more.

Since CNCs remove material from the workpiece by force, it must have a rigid build strong enough to withstand high cutting forces.

The rigid frame is one of the most critical parts of a CNC machine. It is the frame that holds all the other components together.

It also acts as a guide for the cutting tool and provides an accurate path for the tool to follow.

3D printers, on the other hand, use the material in molten or powdered form, thereby eliminating the need for a rigid construction to deliver high force during the printing process.

Supplements

Coolant ON in CNC machine
Coolant pumped in CNC machine

While machining, these machines use certain supplements to provide a suitable machining environment for the tool and material.

For example, CNCs use cutting fluids to lubricate and cool the material-tool contact point. Sometimes they also require dust collectors to keep the work environment clean.

In the case of 3D printers, they use a heated bed to help with the adhesion of the object to the printing surface.

Tools

Threading on a VMC
Threading on a VMC (Source: Seco Tools)

CNCs are versatile machines, they allow you to change the cutting tools to make different types of cuts with varying sizes and finishes.

3D printers lack this flexibility, and the object being printed has a uniform resolution with constant layer thickness throughout the print.

Accuracy and Repeatability

CNC machines can provide higher machining accuracy than 3D printers because of how they work.

The rigid frame of CNCs ensures high repeatability with minimal vibrations, making it feasible for large-scale production, where multiple products with similar dimensional accuracy are required.

On the other hand, 3D printers melt and print the material layer by layer, as a result, the printed parts are prone to slight dimensional inaccuracies.

Surface Quality

3d printed and CNC machined plastic parts
A 3D printed plastic part (left) and CNC machined plastic part (right)

In terms of surface quality, CNC is better than 3D printing. This is because of the wide range of tooling CNCs use.

With different tools like a ball end mill, face mill, sanding belt, etc., CNC can produce workpieces with a high surface quality.

The layer-by-layer printing process of 3D printers leaves behind a rough surface texture on the workpiece.

Today, 3D printed parts are treated with surface finishing techniques such as painting, powder coating, plating, etc., to achieve a smooth surface.

Part Toughness and Tolerance

When compared to 3D printing, CNC machining can produce parts with tighter tolerance and better toughness.

CNCs have a tolerance rating of ± 0.025 mm, while advanced 3D printing techniques like Direct Metal Laser Sintering (DMLS) can only provide tolerance of around ± 0.1 mm.

Also, since CNCs use subtractive manufacturing techniques to sculpt a part from a block of material, it doesn't lose the original toughness of the material.

But a 3D printer adds material layers on top of each other, which are fused together to produce the final product. This reduces the overall toughness of the part, making it prone to breaking.

The minimum line thickness an advanced 3D printer can achieve today is 0.4 mm.

Cost

CNC machines are comparatively more expensive than a 3D printer that provides a similar work area.

Moreover, the need for various accessories such as cutting fluid delivery system, special cutting tools, etc., further increase the maintenance cost of CNC machines.

For small businesses making prototypes, a 3D printer is a cost-effective option as it allows them to create prototypes without needing expensive equipment.

CNC and 3D Printing - The Basics

Additive vs Subtractive Manufacturing

illustraction of additive manufacturing process
Additive manufacturing

Additive manufacturing is a technique that involves the addition of material in a layer-by-layer manner to make the desired part or object. For example, 3D printers work by this principle.

This technique is used for rapid prototyping of parts, production of complex parts, and creation of customized products.

illustraction of subtractive manufacturing process
Subtractive manufacturing

In the subtractive manufacturing process, the material is removed layer-by-layer from a block of the workpiece to create an object.

This is done by using cutting tools and machines such as lathes, milling machines, and routers.

What is a CNC Machine?

Types of CNC machine
Different types of CNC machines

A CNC machine is a computer-controlled tool that can be used for various machining operations like cutting, shaping, and forming different materials.

These machines typically have three axes of movement and can produce complex shapes from raw materials such as metal, wood, plastic, etc.

Numerical control technology has been used in manufacturing for decades. It allows machines to be programmed to perform complex operations automatically.

It is now an integral part of the production process in many industries and can be found in different types of machines.

Some of the common CNC machines include CNC routersCNC mills, CNC lathes, laser cuttersplasma cuttersElectrical Discharge Machines (EDMs), grinders, etc.

What is a 3D Printer?

Printing on a 3D printer
3D printing vase on Snapmaker 2.0

3D printer is a type of automated machine that follows the principle of additive manufacturing and uses numerical control technology to produce the desired part from a CAD file.

These machines create three-dimensional objects by laying down successive layers of material on the work plate until the object is complete.

The most common type of 3D printer is fused deposition modeling (FDM) printers, which work by extruding thin strands of heated plastic, metal, or other materials that cool and harden after being deposited.

Practical Applications of 3D Printing and CNC Machining

The practical applications of 3D printing and CNC machining depend on the material you plan to work with, the kind of part you want to make, the quantity, and how fast you want to make them.

Type of material you plan to use

The materials most commonly used for 3D printing are plastics, metals, and some biomaterials like sugar or wood pulp.

3D printers can also use other materials like ceramics and concrete, but these materials are less common because they require more time and effort to produce than plastics or metals.

Comparatively, CNC machines can cut and mill almost any material. Some popular materials processed on CNC machines are metals, wood, and plastic.

The materials that a CNC machine can cut depend on the machine's build and the kind of cutting tool installed in its cutting head.

PlasticMetal
ABSAluminum
Polycarbonates (PC)Titanium
NylonBrass
Polyetheretherketone (PEEK)Steel

Common types of plastic and metal materials used on CNCs
PlasticMetal
NylonAluminum
Acrylonitrile Styrene Acrylate (ASA)Titanium
Polylactic Acid (PLA)Stainless steel
Acrylonitrile Butadiene Styrene (ABS)Inconel (a superalloy)
Polyetherimide (ULTEM)
Thermoplastic Polyurethane (TPU)

Common types of plastic and metal materials used on 3D printers

Which is best for making metal parts?

A CNC milling machine working on a metal workpiece.
A CNC milling machine working on a metal workpiece.

A CNC machine is best for making metal parts because its rigid build and transmission provide higher precision and accuracy than a 3D printer.

Also, it allows you to make metal parts with high tolerances compared to 3D printers.

What about plastic?

For making plastic parts, both 3D printing and CNC machining are equally good. The better option depends on the number of parts you plan to make.

How many parts are you planning to make?

CNCs are better suited for processing parts in large quantities as they have higher repeatability.

If you are using the 3D printing technique to make similar-looking parts, it can be more costly than CNC machining.

This is because 3D Printers take more time and effort to complete a job, while CNC machines can produce many parts at once or in cycles with little effort.

3D printing is ideal for prototyping applications where fewer parts (less than 10) are to be manufactured, whereas it's better to consider using a CNC machine if you want to make more parts.

For larger objects, consider CNC machining techniques like casting or injection molding, as they are cost-effective for manufacturing parts in large quantities.

Which is best for prototyping?

Though both 3D printers and CNCs can make custom parts or prototypes, 3D printers are much more effective as it allows for multiple revisions at a lower cost.

Therefore, various industries, like engineering, architecture, design, and medical fields, use 3D printers for prototyping.

Will 3D Printing Replace CNC Machining?

Within the short period of the 3D printer's existence, they were able to partially replace CNCs used in the field of medicine, architecture, product design, etc.

Due to their controlled material deposition printing technique and ability to produce complex shapes, 3D printers are now increasingly used for making architectural models and real-life structures.

Medicinal prosthetics applications like dental implants, orthopedics, etc. today use 3D printers to make different parts like never before.

These manufacturing shifts seen in these industries are a clear example of how 3D printers can replace CNCs in the near future.

Even though 3D printers are capable of replacing CNCs in various fields, they still can't replace CNCs when it comes to manufacturing parts with high precision and tight tolerance.

Also, the wide range of materials CNCs can work with is a massive advantage of CNCs over 3D printers.

So, in short, CNCs are here to stay. Even though they have lost importance in some industries, they are the most commonly used machines in the manufacturing industry.

It might be difficult to say whether one will completely replace the other. But in the future, they will be used together to produce complex shapes and prototypes.

In fact, hybrid 3D printers having CNC capabilities are currently used by some industries.

Traditionally, printing and cutting were performed with separate machines, but these hybrid printers or CNCs can perform both tasks on a single machine.

I have reviewed Snapmaker 2.0, which is one such miniature, an early model of hybrid machines.

Final Thoughts - Who Wins?

Since the introduction of 3D printing in the manufacturing sphere, it has taken up some portion of work from CNCs, but they couldn't take it all.

A significant proportion of work is still being done by CNC machines like mills, lathes, routers, and grinders.

CNCs and 3D printers are like part of a puzzle. They both have their places, and both are required to make it complete.

They have different capabilities and come in handy while machining different parts and objects for different applications.

Frequently Asked Questions

Is CNC the same as 3D printing?

Technically yes, but functionally no. Like CNCs, 3D printers are also computer controlled and operate in a similar fashion, but CNC uses subtractive manufacturing techniques while 3D printers use additive manufacturing.

Which is cheaper? CNC or 3D printing?

3D printing is cheaper than CNC because it uses comparatively less raw material when creating an object. 3D printers are also priced less and don't need to use special tooling or setups before starting production.

Is CNC faster than 3D printing?

In general, CNC is faster when compared to 3D printing. This is because the cutter on a CNC can remove materials faster than a 3D printer could extrude and deposit the material.

About John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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John

Hey I'm John. I talk about CNCs and Power Tools at Mellowpine. I'm a CNC hobbyist who has been making CNCs and writing about CNCs for a while. I currently also work as a consultant for business owners and hobbyists setting up their own CNCs. If you have any questions related to CNC, I'd be happy to answer them. Reach me at john@mellowpine.com

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