7 Things That Can Not Be 3D Printed

With all the parts, models, and designs available today, you’d think that 3D printers can pretty much do anything. After all, they’re being used by everyone, from hobbyists to prosthetics experts. Still, there are some things that just don’t work – well, not yet, anyway. 

Here are 7 things that cannot be 3D printed: 

1. Perfect spheres without supports
2. Flammable natural materials 
3. Hard natural materials, such as stone 
4. Certain metals, including gold and silver
5. Large and intricate objects 
6. Complicated designs 
7. Completely finished products

Let’s get into the details and talk about why these materials and shapes aren’t always compatible with 3D printing. I’ll also discuss the exceptions to these rules and tell you about some of the newest ways engineers work around the limitations of 3D printing. 

1. Perfect Spheres Without Supports

Spheres and perfectly round objects are among the most challenging things to 3D print. This is because, as with every design and model, there must be a base onto which you print. 

In most cases, there is a flat base that filament is built upon. Without it, anything round would roll away, interrupting the print. 

That said, it is possible, provided you use some kind of support. Unfortunately, these supports will leave residue behind, which needs to be sanded away once the print is finished. 

Check out this video to see how it can be done:

So, if you want to print a sphere, you will need to ensure that you use proper support structures and prepare for quite a bit of sanding and processing to even out the shape.

As of right now, it doesn’t seem like this problem with spheres will ever go away since you will almost certainly need a print bed to print anything, and to keep a globe on the print bed, you will need something flat to stabilize it. 

2. Flammable Natural Materials

3D printers use heat to melt down materials and shape them into objects. As a result, they cannot print using materials that don’t tolerate heat. 

These materials include:

• Paper
• Wood
• Organic textile fibers 

Still, engineers have developed some filaments that contain small amounts of these organic materials. Although they will never compare to the real thing, they often look similar to the original material. 

Wood Filament

Wood filament usually includes about 30% wood particles (sawdust), an exception to the rule of 3D printing with flammable materials. However, this wood usually burns a bit during the printing process. 

The wood particles are also always mixed with another filament such as PLA, making it less durable and lighter-feeling than natural wood. Wood filaments also usually contain something like cork, which is fire-retardant, to keep your printer from going up in flames. 

Textile Filaments

Fabrics, too, are possible to 3D print, but materials such as cotton, hemp, and linen are far too flammable to be used. 

Instead, textile printing experimenters use materials such as flexible TPU and TPE. 

Still, this intelligent option for fabric production hasn’t made it off the runway yet. That’s because the processing time and materials necessary to print these designs aren’t any better than the traditional processes used to make cotton and other natural fabrics. 

In addition, most 3D printed fabrics aren’t tightly knit, which usually leaves TPU and TPE fabrics looking like a holey fishnet. So, right now, making clothing and other fabrics with 3D printing methods isn’t possible. 

Paper is far too flammable to print like wood and other natural fibers. 

So, 3D printing is not the way to go for natural materials. Although 3D printing can make convincing dupes to materials such as wood, fabric, and paper, it can’t manufacture these items efficiently or competently. As a result, the finished product doesn’t often compare to the original. 

3. Hard Natural Materials, Such As Stone

Like the other natural materials on this list, stone is impossible to 3D print. Rock is far too hard and heat-resistant to turn into a filament, so, by and large, you can’t use it in 3D designs. 

However, there are two workarounds:

Stone-Filled Filament

Stone-filled filament usually contains PLA and stone powder, making your models look a bit like concrete. These are generally made with softer stone varieties such as:

• Marble
• Terra cotta
• Concrete
• Granite

These filaments are much like wood ones because they only contain small quantities of natural materials, and the end products still have a plastic-like feel. Likewise, the durability of stone-filled filament prints does not compare to raw, pure stone. 

Stone-Mimic Filaments

Stone-mimic filaments don’t contain any stone particles, but they can give your 3D prints a stone look. Such prints are not fireproof, which makes 3D printing with stone-inclusive and stone-look filaments more of an aesthetic choice than anything. 

As of right now, it is frankly impossible to 3D print something as durable and heat-resistant as stone, and it will likely be a very long time before we can make convincing stone objects with fire resistance and durability using a 3D printer. 

4. Certain Metals, Including Gold and Silver

While 3D printers recently added metal filaments such as aluminum, stainless steel, cobalt, titanium, and nickel alloys to their repertoire, you can’t 3D print with all metals. Instead, you will have to use metal clay or metal powders. 

Metal clay is just what it sounds like – clay with metal powders incorporated into it. Metal powders are usually pure metal fragments. 

Printing With Metal Filament

When you make a metal 3D print, a specialized printer will deposit a layer of hot metal powder or clay onto the print bed. Then, it will use a laser to heat and melt the metal. 

In another printing process called metal binder jetting, the 3D printer deposits chemicals onto the metal powder or clay, which causes a chemical reaction that bonds and hardens the metal to itself. 

Metals That Won’t Print

However, not all metals are compatible with 3D printing. According to metal manufacturing experts at Equisphere, when 3D printing metal objects, you need “a metal with high fluidity, high distribution density, low moisture absorption and high chemical stability for when the laser heats up.” 

Because of these limitations, it is difficult and often impossible to print with materials such as gold, silver, tungsten, molybdenum, and several other common metals. 

3D printed metals also often have issues with structural integrity that make them unsuitable for use in heavy-duty machinery such as manufacturing equipment, automobiles, and airplanes. In addition, metal 3D printed parts usually have high porosity, making them prone to crumbling, cracking, and warping. 

However, you can likely expect metal 3D printing to get much more advanced in the coming years since it is a relatively new invention in itself, with the first metal 3D printer coming out in 1994. 

5. Large and Intricate Objects

3D printers are small, and even the largest of them cannot tackle a project like an extensive and intricate car or a big piece of machinery. 

While they can print large or complex objects, they cannot usually do both. 

Large Printers Need Larger Nozzles

For example, let’s look at the largest 3D printer in the world, a $2.5 million printer at the University of Maine. This printer is massive, with a 100-foot (30.48 m) print bed that is suited for making items such as boats and architectural components. But it is not ideal for creating a working machine. 

A larger printer comes with a larger nozzle, and it will accordingly use thicker filaments, making tiny details harder to print with accuracy. 

Printing a finished product, complete with fine-tuned mechanisms, is impossible right now. With a printer this immense, you could create the casing for a machine, but it’s almost impossible to ensure finer details. 

Instead, you’d need to use a large printer for bigger pieces and several smaller printers for the more intricate parts.

However, the investment in machinery usually isn’t worth it. That’s because the processing time will be longer, the cost of materials will be higher, and the parts won’t be as durable as molded or cast parts. 

Still, with this vast 3D printer comes promise for a more advanced future in 3D printing, and one day, likely soon, we will see printers that can produce seamless, fully-functional machines. 

6. Complicated Designs

Although some complicated designs, from small, humanistic 3D figurines to scale models of ancient artifacts, are possible to 3D print, not every design is feasible. 

Intricate Spirals Need More Structure

For example, I recently read this article, which discusses a specific design for drone propellers. Unfortunately, they found that the design was far too complicated for even professional 3D printing services to attempt. 

This small, round, spiral-shaped propeller, conceived after Leonardo Davinci’s propeller designs from the renaissance, wasn’t anything special at first glance. It had smooth surfaces and a coiling seashell-shaped design. However, the perimeter’s width-to-height ratio, the spiraling shape, and the lack of scaffolding were too much for a 3D printer to produce accurately. 

This model is a perfect example of the limitations of 3D printing. 3D printers often have difficulty printing round objects since each layer of the print builds upon the previous layer. Therefore, the printer will likely struggle to make the layers meet up properly when printing a spiraling tower. 

Pieces With Overhanging Areas Often Won’t Print Properly

In addition, the overhanging edges of the print, which had no support towers or bridges, created areas where the 3D printer could not connect each perimeter. Without any scaffolding, infill, or support, the 3D printer would have failed. If anyone tried to make it, the print would have looked like a shapeless lump on the bottom of the print bed. 

In this case, the drone enthusiast had to make a mold and cast the propeller themself, but they were able to use a 3D printed prototype, complete with infill and scaffolding, to make the mold. 

So, even if something looks simple, that doesn’t mean that it will be possible to 3D print. 

Sometimes, even the most miniature, smoothest design is too intricate for a 3D printer, especially when it comes to overhanging parts, spiral designs, and hollow interiors. 

7. Completely Finished Products

When you 3D print a design, nine times out of ten, you’ll need to finish it by hand. This might include: 

• Sanding off layer lines 
• Waterproofing the object 
• Clipping off support structures 
• Removing rafts depending on your design and the desired use for your product 

Post-processing is something that goes hand-in-hand with 3D printing, and very few printers can create seamless, smooth, airtight models without some manual labor. 

So, when you want to make something once and be done with it without refining your product, 3D printing isn’t your best option. 

3D Printing Isn’t Always Consistent

In addition, though 3D printing is ideal for small parts and homemade objects, when it comes to making reliable, high-quality prints every time, 3D printing isn’t as efficient as other methods. 

Since each part that you 3D print needs some processing before using it, printing large machines, cars, phones, laptops, and other completed items with one design is impossible with a 3D printer. 

For example, if you printed a small gear mechanism with two gears and a crank handle straight from the printer, you wouldn’t be able to sand off the gears. Without sanding, the layer lines could interfere with the smoothness of your mechanism, making it challenging to turn and use. 

For now, we will have to be satisfied printing small parts, smoothing them out, then assembling them later. 

3D Printing Isn’t Always Precise Enough for Manufacturing

This limitation to 3D printing significantly impacts manufacturing, where efficiency is everything. However, when you are printing small parts at home, it likely won’t stop you from making your own designs. 

In a factory setting, finishing a 3D-printed object takes care and time. Unfortunately, in industrial applications, that care and time mean more money, which makes the roughness and unreliability of 3D printed objects undesirable. 

So, in a factory setting, most manufacturers still use tried and true methods such as injection molding to ensure that their products have a seamless, uniform surface without any need for sanding or refinement.