Manufacturing Transitions: Moving Between CNC Machining and 3D Printing

–  Bailey Hudson

Neither CNC machining nor 3D printing is a new technology. Computer Numerical Control (CNC) has been around since the 1950s, while 3D printing was invented in the mid-1980s. But both technologies are in increasing use today. CNC has become one of the dominant machining methods, with CNC lathes, mills, and routers fast becoming the standard.

As for 3D printing, technology has taken off in recent decades years. With its ability to produce almost any shape, many manufacturers have started to ask about the exact relationship between CNC machining and 3D printing. How do the two technologies work? Can they be used together? Will it ever be possible, or practical, to abandon CNC altogether for 3D printing?

In this article, we’ll look at some of those questions, and suggest some ways that a manufacturer could use both methods in conjunction.

Similar goals, different methods

Both CNC and 3D printing are machining manufacturing techniques, but they take a radically different approach. CNC is a subtractive process whereas 3D printing is an additive process. With CNC, Tto make a cylinder, for example, you might begin with a vaguely rectangular shape, then use a lathe to machine away excess material until the workpiece was cylindrical. The resulting piece will be smaller than the one you began with; you’ve removed material to make the part.

3D printing is the exact opposite. With 3D printing, you begin with no shape at all – simply the printer itself and a metal powder as raw material. The powder is used to slowly build apart from the ground up, adding material layer by layer.

Additive machining manufacturing provides a whole new approach for manufacturers. 3D printing can produce almost any shape, including geometries that might be difficult to achieve through subtractive machining. The potential applications for 3D printing are nearly limitless, with special potential for prototyping and R&D.

Pros and cons

So why not simply abandon CNC subtractive machining-manufacturing and move everything over to 3D printing? Why not stop cutting metal parts (subtractive machining-manufacturing) and only build them instead (additive machining manufacturing)?

Unfortunately, 3D printing does have some drawbacks. First and foremost, the process is quite slow – far slower than the various subtractive machining processes. Large-scale, industrial-sized projects would require a much longer time to build than to cut, particularly if there is a large number of parts to produce. Thus, one of the first questions many manufacturers use to determine the correct method to use is simply to ask, “how many parts do I need?” If the answer is a large number, CNC is likely to be much faster and more efficient. 3D printing also produces parts with much larger tolerances than CNC machining, meaning the parts can be a bit rougher and still in need of finishing. 

Two are stronger than one

The greatest potential for both methods comes when they are used in conjunction with each other. For individual parts, 3D printing provides a way to produce one-off or small runs of parts with geometries that would be difficult to cut on a CNC machine. After the 3D printing is complete, the same part could then be subtractively machined via CNC to finish surfaces, insert threaded holes, or any number of other machining steps.

The two methods can also be used in the overall workflow. 3D printings excel at producing prototypes and models, parts that are often one-off productions or require small numbers, and where the time pressure is not great. Once a part has been prototyped and the design refined, a CNC program can be made that allows operators to produce the part in far greater quantities on a CNC lathe or mill.

Used in this way, the manufacturing process starts with additive machining manufacturing and then moves to subtractive machining-manufacturing, to produce even a difficult or completely new part with tight tolerances.

Back and forth

Using CNC machining and 3D printing isn’t a matter of transitioning entirely from one to another, but of using both technologies at once. In the real world, that means being flexible and deciding on a case-by-case basis which method is best for a given part. 

MJ Engineering Knows 3D Printing!

In addition to their fused deposition modeling (FDM) desktop 3D printer (see 3D Printer Series—Part 1), MJ Engineering also owns a stereolithography apparatus (SLA) desktop 3D printer. The SLA printer from formlabs is used to make parts for test fits and dry runs.

3D printing materials-SLA

The SLA printer uses photosensitive thermoset polymers in liquid form. An ultraviolet (UV) laser beam selectively hardens (cures) the polymer resin, layer-by-layer, through a process called photopolymerization, which creates strong unbreakable bonds. As the part is being built, the build platform rises, lifting the part upward, out of the resin bath.

Is an SLA printer worth it?

Although the FDM printer can make parts that are stronger and more durable, the SLA printer is ideal when high accuracy or a smooth surface finish is desired. The SLA printer excels at tight tolerances, to the tune of plus or minus one thousandth of an inch—10 times more precise than the FDM printer.

3D printing materials-FDM

MJ Engineering’s Markforged FDM desktop 3D printer builds parts using a black thermoplastic filament called “Onyx,” which is primarily used when parts are needed to check form, fit, and function. The Onyx plastic can be reinforced with different continuous fibers, depending on the intention for the part being printed. Some examples of fill materials used with Onyx are:

  • Fiberglass—basic, cost-effective reinforcement material
  • High strength, high temperature (HSHT) fiberglass—to maintain strength in high-temperature settings
  • Carbon fiber—to withstand fatigue and improves stiffness and strength
  • Kevlar—to endure high impact and high deflection applications

To add the reinforcement material, the 3D printer uses two different nozzles. One nozzle dispenses plastic (Onyx), while a second nozzle dispenses the reinforcement material in the locations specified by the software. Typically, the reinforcement material is internal to the part and is enclosed in plastic.

Putting parts together

If a part fits within the parameters of the printer’s build plate and height restrictions, it can be printed as one piece. Otherwise, it can be bolted or glued. For example, as a test for a machine MJ Engineering is working on, a part like the one pictured here can be printed out of Onyx on the FDM printer in two pieces and then superglued. Once the finalized design is determined, the printed part can be bolted to the actual machine. “We can make sure it works the way we want it to and there are no flukes,” says mechanical engineer JC Kraml, “before we send it to our machine shop and spend 100 times more.”

To discover more methods by which MJ Engineering is using 3D printing to improve its projects, parts, and processes, check out Part 3 of our 3D Printer Series.

MJ Engineering’s New 3D Printer Adds Value Every Day

When you design custom machines like MJ Engineering does, things don’t always go as planned. That’s OK. Their engineers are experts at solving problems and improvising when necessary. Nonetheless, making customer design changes partway into a project can cost weeks on the schedule and thousands of dollars in parts. To reduce such risks and be more responsive, MJ Engineering recently purchased a Markforged desktop 3D printer.

How it works

The fused deposition modeling (FDM) printer heats a thermoplastic filament to its melting point and extrudes it through a nozzle, layer by layer, to create a threedimensional object. Precisely following a design in a computer program, it can print production-ready parts that are strong, rigid, and durable.

Is having a 3D printer worth it?

“There are great benefits to using these,” says mechanical engineer JC Kraml, one of MJ Engineering’s resident experts at 3D printing. He praises their new printer for helping avoid project bottlenecks, saying, It’s fantastic at quick fixes and helping move projects along; it’s great to have for that purpose alone.

A few of the 3D printer’s many applications include:

  • Rapid prototyping
  • Concept modeling
  • Making replacement parts

Kraml recently used the printer to build a prototype part for a speaker installation jig. It enables us to fail faster,” he explains, meaning we can quickly solve problems that may arise during the design or assembly process. And we save time and money because we manufacture parts inhouse.

Before purchasing the FDM printer, MJ Engineering relied heavily on their machine shops to make parts. After getting the part, which would typically take weeks, there was still a chance it wouldn’t work, meaning more expense and more waiting.

Our new 3D printer allows us to respond rapidly,” says MJ Engineering President Richard Wand. “If a part doesn’t work, or it doesn’t fit the first time, we can tweak the design, reprint it, and have a new part in a matter of hours.”

Despite its advantages, the 3D printer is not going to replace MJ Engineering’s machine shops any time soon. Larger parts and parts that need to be made of metal will still be fabricated elsewhere, at least for now. In the long term, Wand says the new printer will be good for his company.

It will be good for MJ Engineering’s customers, too. In addition to printing prototype and production parts for their own projects, they can print parts for others who may not have enough need or know-how to make a permanent investment in a 3D printer.

Suffice it to say, MJ Engineering’s new FDM 3D printer adds value with every part it prints!

3D Printing Services

MJ Engineering now offers 3D printing services, and we are proud to show off our latest acquisition—a Markforged Fused Deposition Modeling (FDM) 3D printer.

What is 3D printing?

3D printing, or additive manufacturing, is a process of making three-dimensional solid objects from a digital file. To build the object, the printer lays down one layer of material at a time, precisely following a design in a computer program. The object can be made from a variety of materials, including plastic and plastic reinforced with carbon fiber or Kevlar. It can take anywhere from 45 minutes to 24 hours to print a part—much faster than most traditional manufacturing methods.

Benefits of 3D printing

The number of companies choosing to use 3D printers is adding up! Being able to quickly print a part to solve a problem can be a big time and money saver. Some advantages of 3D printing include:

  • Speed at which parts can be produced
  • Complexity and design freedom
  • Customization
  • Increased flexibility in production flow
  • No wasted material
  • No need to create specific tooling or use several tools

Let MJ Engineering 3D print it for you

Our 3D printer has already revolutionized the efficiency and efficacy of how we do things here at MJ Engineering, and now we want to share it with you. After all, not every company has enough know-how or need for a 3D-printer to justify buying one. No problem! MJ Engineering has already made the investment. Whether you need to rapidly assess if a part will work before committing it to production, or you know the part you want and need it to be produced quickly—we can help. With our 3D printer, we can create parts as needed, much faster than a machine shop. Read a Dunlop Systems case study and how they produce custom tooling for their facility, saving tens of thousands of dollars with their own Markforged 3D Printer. This case study is very similar to the work MJ Engineering is doing with their own Markforged 3D Printer.


Watch our 3D printer at work

Our engineers are always finding new practical uses for the 3D printer; they use it to solve problems practically every day. In fact, it has hardly stopped running since we got it!

“It’s fascinating to sit and watch; it’s a beautiful machine.”
–Richard Wand, President of MJ Engineering