Source: All3DP

Resin vs FDM Printer, Which is Right for You? Read on to get all the most important information about the two main types of printers.

In today's desktop 3D printing market, the two most popular areas are fused deposition modeling (FDM) and resin-based printing. While generalizations and assumptions can be (and are) made about their differences (eg FDM is cheaper, resin is better for detail), there are a few more things you should know before making a decision and to choose one over the other.

In this article, we'll dive into the differences between the two, discussing technology, materials, individual strengths, price ranges, and more.

FDM printing

FDM, also known as layer-on-layer (Source: 3MG Bonev Ltd.)

FDM 3D printing is a specific 3D printing technology that falls under the broader additive manufacturing category of "material extrusion". As the name suggests, each machine falling into this category extrudes material into specific patterns to produce a final shape, with FDM using molten plastic (sometimes combined with other materials) as the extrusion medium.

FDM works much like a hot glue gun: a solid filament is fed into a hot nozzle, which melts it and allows it to flow and be laid in flat layers. In the case of a printer, these movements within a layer are precisely directed (for the most part) along the X- and Y-axes of the Cartesian coordinate system. The first layer is deposited on the printing surface, cooled and solidified quickly. Another layer is then added on top of the last one and the process is repeated, building the 3D object slowly, layer by layer.

Unlike resin printing, where there are different approaches to the actual printing process, in FDM printing, the process of extruding and depositing hot plastic is fairly similar for all machines. This is why all FDM printers technically belong to the same technology. However, there are of course different types of FDM printers, with the most popular style being the rectilinear printer (also known as a "Cartesian" printer, although this can be confusing).

The area where the biggest changes are occurring are multi-material printers, which can print multiple colors and materials in a single print. Additionally, some single-extrusion FDM printers can be upgraded with add-ons such as Prusa's MMU 2S and Mosaic Palette 2S Pro.

Resin stamp

Source: All3DP

"Resin printing" is more of a general term for 3D printing technologies that fall under the category of bath polymerization additive manufacturing.

Most resin printers have a container with a clear, flexible bottom sheet, also called a tub, that is filled with a photosensitive resin that hardens when it comes into contact with UV light. A build platform is then immersed in the bath and a light source beneath the transparent bottom cures the resin to the specifics of the model, bonding the cured first layer to the platform.

The build plate is then moved up to make room for the next layer and allow the new resin to flow between the previous layer and the bottom of the tub. This new layer is then cured by the light source and the process is repeated until the finished 3D object is created.

The differences between the types of resin printers lie in the way the light is generated and applied to the resin. These technological differences mean that each of the following types of resin printing has its own technology.

LCD printing

LCD printers like the Photon S give some fine details (Source: All3DP)

The most affordable form of resin printing is called LCD printing (also known as MSLA printing). The LCD printer uses a powerful UV light source that can illuminate an entire layer at once. This light is selectively blocked and transmitted by a liquid crystal display (LCD) screen located above the UV light. The LCD displays a negative image of the layer to allow light to pass through only where the resin needs to harden.

The use of this technology is said to sometimes reduce print quality, as the resolution of the LCD screen determines the print resolution. In return, LCD is also the fastest type of resin printing. LCD printers are the cheapest types of resin printers and are therefore more suitable for beginners and hobbyists.

SLA printing

The first type of resin printing (and indeed the first type of 3D printing) was SLA, which stands for stereolithography. Unlike LCD

This technology is very similar to LCD printers, but the light source used is a laser. This laser is directed around the tub by a motorized mirror that can change the angle of reflection. The laser outlines the resin in the shape of the current layer, much like a regular FDM 3D printer nozzle outlines a new layer point by point.

This technology is often more expensive than LCD due to the increased complexity and number of moving parts, but usually boasts a high resolution.

DLP printing

The latest popular resin printing technology is DLP printing, which uses a Digital Light Processing (DLP) projector. The technology is quite similar to LCD printing, as an entire layer is exposed at the same time. The difference between the two is how the light hits the resin in a certain shape. Specifically, the projector projects an image onto a series of mirrors, which in turn direct the reflected image to the bottom of the tub without the need for an additional screen to block out unnecessary light.

This printing method is the least common of the three mentioned here, as its print quality is affected by the resolution of the projected image, which often leaves small pixels on the finished print. From a "historical" point of view, DLP printing can be said to have paved the way from SLA to LCD printing.

Materials

Some things are only possible with FDM (Source: ronfoss via Cults)

By the nature of how they work, there are major differences between the materials used for FDM and resin printing. However, there is great diversity within each of the two groups.

FDM

The main requirement for FDM printing material is that it has a thermoplastic base. These materials are available in the form of a long plastic thread with a diameter of 1.75 or 2.85 mm wound on a spool.

The most popular type of material is called polylactic acid (PLA); it is the most used wire because of its ease of use and high quality. The material is also almost odorless and is one of the least environmentally harmful materials for 3D printing. There are many things that can be printed with PLA, including models that can be in contact with food, assuming that one chooses the right certified brands.

Another very popular material is polyethylene terephthalate glycol-modified (PETG). This material, like PLA, is very easy to use, but has much better mechanical properties, such as higher strength and increased flexibility. The main difference is that PETG prints at around 245°C, while PLA prints at around 200°C. PETG is great for a variety of applications, including models that are exposed to various weather conditions or that require more strength or durability.

Different threads have different uses given their properties (Source: All3DP)

Some more advanced FDM materials, such as ABS or carbon-filled nylon, require a special printer and safety settings before successful use. These materials often require higher nozzle temperatures than PLA and a heated print bed to prevent the material from shrinking as it cools.

These advanced materials also benefit from a casing surrounding the print area. Enclosures not only keep indoor air even, but also prevent harmful fumes from escaping. They can have many negative effects, from simply smelling bad to being harmful to the respiratory system. To prevent this, many high-end machines have built-in filtration systems that filter indoor air and remove particles.

The flexibility offered by filaments and the printing technology behind them should not be underestimated: wood, silk, marble, transparent, glow in the dark, color changing and rainbow, just to name a few PLA options, as the abundance of different combinations with carbon fiber, metal, PC, nylon and even recycled filament means that FDM prints can take on many different forms and applications.

It is also worth noting that the thread must be stored properly and may even need to be dried before use, as most are hygroscopic.

Resin

Resin prints start as liquid in a bathtub (Source: All3DP)

With resin printers, the choice of materials is a bit more limited, but still very flexible, ranging from simple plastics to castable, flexible and water-washable ones. All resins are stored in either UV-resistant bottles or pouches, which prevent UV rays from entering and impinging on the liquid, which would harden the resin prior to use.

Different resins will have different print settings such as exposure time – something that can also be affected by the color of the resin.

It's worth noting that while some brands offer a wider variety of colors, to get a multi-color print, you'll need to print the parts individually. Alternatively, one can paint the resin for different results.

The technology used can affect the resin selected. Resins cure differently depending on the wavelength of light and as such proper compatibility must be checked depending on the print setup. SLA lasers typically emit wavelengths of about 395 nm, while LCD and DLP printers have wavelengths of about 405 nm.

Resolution and quality

Resin (left) and FDM (right) prints (Source: Brianhsv via Reddit)

FDM and resin printing generally differ in the quality and resolution of their finished prints. These factors range from overall appearance to the quality of small details, but also include mechanical factors such as strength.

FDM

One of the most obvious differences between FDM and resin printing is resolution. Because FDM printers use molten layers of plastic to create patterns, the results tend to be less precise and accurate, as the material is typically deposited in 0.4mm wide lines. The actual layers are also large compared to resin printing, ranging from 0.1 to 0.35 mm per layer. This layer height creates visible lines on all surfaces and often prevents FDM-printed parts from being used as final models.

To solve the problem of visible layer lines, the finished print can be sanded or even smoothed with solvent vapors. These methods can make FDM prints look perfectly smooth, but they take time and skill to get right and will also fade small surface details.

Another quality of finished prints is their strength. At this stage, FDM usually performs better than resin printing and depending on the material used is affected by certain print settings. For example, using a high infill percentage, an appropriate infill pattern, and increased wall thickness will make the part stronger, but in turn will increase print time.

Resin

On the other hand, resin printers usually create a much more detailed model. For this reason, resin printing is great for miniatures or high-detail models that are worth the extra effort.

Because of the technology, layer heights are incredibly small, ranging from 10 microns (0.01 mm) to 100 microns (0.1 mm). The standard layer height is 50 microns (0.05 mm), about a quarter of an FDM print. The XY resolution is also in this range.

This low layer height allows for incredible detail and high-quality objects to be printed, with finished prints often showing no traces of the layers themselves, but rather looking like one smooth, solid piece of plastic. Finished prints can also be sanded to achieve even greater smoothness, but this step is in most cases unnecessary because the layers are already so small.

When it comes to strength, strong resins produce printed parts that are generally stronger than FDM. However, this is a difficult comparison because it depends on which FDM materials are being compared.

Speed

Smaller layers will mean less imperfections but more time to print (Source: All3DP)

Another big difference between FDM and resin printing is printing speed. This depends on many factors, including the specific technology used and print settings.

FDM

The time it takes for an FDM printer to complete a print depends mostly on the size of the object being printed, as well as the chosen layer height, fill and speed. Simply put, the larger the item and the smaller the layer height, the longer it will take to print and vice versa.

Another setting that affects print time is fill density. The higher the fill density, the more fibers must be laid down by the printer and the longer it takes to print.

Resin

When it comes to resin printing, the printing time is a little simpler. With LCD and DLP printing, layers cure quickly, as the entire layer cures in 2 to 10 seconds, no matter how much resin is cured per layer. With SLA machines, the printing time is significantly longer because the laser has to reach every point.

Other variables that affect print time are Z-axis height, layer height, and the time it takes the printer to move the print bed up and back down for the next layer. Regardless, assuming one is using an LCD printer, it can be said that resin printing is significantly faster than FDM printing in most cases.

Easy to use

Print being prepared with UltiMaker Cura (Source: All3DP)

Ease of use of a 3D printer is an issue for both beginners and advanced users, as more work means more time spent not printing (or doing other things). Different FDM and resin technologies have many advantages and challenges.

FDM

FDM printers are generally easy to use and therefore quite beginner-friendly.

After loading a thread, starting printing is pretty much all that needs to be done. Once the impression is ready, it should be easy to remove and in most cases can be used immediately for its intended purpose. Some prints, such as waterproof containers, may require either very fine adjustments or some form of coating to be fully ready for use. And as mentioned above, post-processing may be necessary to achieve a certain aesthetic.

Naturally, there are still some issues with FDM printers, including stringing, warping, and elephant feet. FDM machines generally require more maintenance and calibration to prevent these problems from occurring.

Resin

Resin impressions are cured with UV light (Source: All3DP)

Unlike FDM printing, resin printing requires a bit more to be safe and successful. First, the resin is toxic, meaning it is not safe to touch, and the fumes are not safe to inhale. Because of this hazard, gloves and masks are required when handling resin and impressions before they are fully cured.

A key feature of all resin printers is that they have a cover that covers the build area and resin tub. These covers are often clear orange or red plastic. Their main jobs are to block UV rays from hitting the uncured resin in the vat and to protect viewers' eyes from the UV light in the printer. In addition, the hood is designed to keep toxic and often smelly fumes from spreading.

Once the resin is loaded into the machine's vat, the printing process is relatively simple. But a print just removed from a printer is still covered in uncured resin. This resin must be washed away using a solvent, in most cases isopropyl alcohol. The print must then be fully cured under an ultraviolet light source such as a special lamp or simply in the sun to bring it to its final state. Once all these steps have been completed, the print can now be processed normally and is no longer toxic.

These extra steps mean that resin 3D printing has a higher learning curve, so it's not necessarily as beginner-friendly as FDM printing. In addition, the general workspace will also need to be larger and equipped with additional supplies and equipment (for curing and washing).

Resin printers have some common issues that lead to failed prints, but these are usually easier to resolve than FDM printers. The biggest point of failure is that the cured layers do not adhere to the build plate.

And as a final and equally important note, proper resin disposal is a must.

Price

Different printers have different price tags (Source: All3DP)

Another deciding factor is the price of both types of printers. Both technologies can be purchased relatively cheaply, with machines available in the $200 range, but as size and quality increase, resin printers become more expensive faster than FDM printers.

As far as FDM goes, there are great options under the $200 , under the $300 , and under the $500 , although the ones with higher build volumes can be a bit more expensive. However, while there are excellent polymer printers out there, the larger ones are at least double the price of the larger FDM printers. For example, the Phrozen Sonic Mega 8K large-scale polymer printer costs ~$2200 with dimensions of 330 x 185 x 400 mm. In contrast, an FDM printer like the Anycubic Kobra Max costs just $570, with a build volume of 400 x 400 x 450mm.

In addition to the printers themselves, maintenance can be more expensive for resin machines. Resin LCD printers require new screens after about 2,000 hours of use, and the cost of screens depends on size. On the other hand, although less common in the hobbyist market, DLP printers offer around 20,000 hours of operation. Meanwhile, the maintenance costs of FDM printers are usually negligible because there are many spare parts available.

Which one?

If you're looking for impressive detail… (Source: All3DP)

Now to the most important question: Who is right for you?

All in all, if you're looking for a machine that you can customize to print a little bit of everything, the FDM is for you. These machines are ideal for printing a wide variety of objects at reasonable quality, from large structural brackets that are strong enough to withstand heavy loads, to smaller, low-detail models and accessories.

But when it comes to small patterns and impressive details—prints that take advantage of the material's transparency, strength, or flexibility, or a venture into jewelry embossing—resin printing may be the way to go. While the learning curve may be a little steeper and the initial investment may be a bit higher, it's still a decent option for hobbyists.

The swing in one direction or the other (if necessary) will basically come down to the following: What do you want to print and what will it be used for?


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