Original Prusa SL1 Review: The MK3S for Resin?

One does not have to be a 3D printing enthusiast to have come across the name Prusa. Few brands have the impeccable reputation and fervent fanbase that Czech-based Prusa Research enjoys.

Creators of the Original Prusa i3 MK3S, which currently boasts All3DP’s Best 3D Printer award, Prusa Research achieved its goal of creating a high-quality open-source 3D printer accessible to the masses. For the SL1, the company has set out to do it again — this time tackling desktop Stereolithography (SLA) printing.

To help them with this massive undertaking, Prusa acquired the Czech company Futur3D, which already specialized in SLA 3D printing and had five years of experience in the field.

“The SL1 isn’t trying to compete with the flimsy Photon or with the ultra-pricey Form,” said Prusa himself, “but instead I want it to be the MK3 of the resin world – have the best print quality, convenient design and features, ease of use and other things, while keeping a price accessible for an everyday hobby maker.”

So, did Prusa succeed? Read on as we review this printer and find out if the master of the maker scene, Prusa, came through on his words – once again.

Verdict

PROS

• Complete ecosystem with the CW1
• Minimal setup
• Comprehensive build guide (if you get the kit)
• Slick design
• Compatible with third-party resin
• Replaceable carbon filter

CONS

• Relatively small print bed, for the price
• Washing turbine (CW1) does not function properly
• Slicer estimated time is inaccurate
• Supports sometimes lose adhesion to bed at fringes
• Bed raising not possible mid-print

It’s no secret that Josef Prusa and his team are striving for perfection. And yes, the SL1 is on the right track, but its also not quite there yet in terms of his own ambition.

Compared to the budget resin printers Prusa has clearly stated he is not competing with, the SL1 does offer a bouquet of convenient features that give users the Prusa-feeling of a well designed and harmonized machine. You can expect high-quality prints with little effort even without any prior 3D printing experience, just as Prusa’s goal is.

However, for the price tag, the downsides of the printer can also not be too easily overlooked.

We think of the SL1 as the MK2 on Prusa’s way to creating the MK3S of the resin printing world.

Much like the DLP process, MSLA effectively cures an entire layer at a time as opposed to the point-to-point technique of traditional SLA printing and can, therefore, achieve significantly faster print times. The downside being, with MSLA, the pixel size of the LCD photomask defines the granularity of a print.

Using a 5.5″ 2K LCD screen, the Original Prusa SL1 offers a possible XY-resolution of 47-microns. Paired with a recommended layer height (Z) of 0.025 to 0.1 mm, the SL1 is capable of incredibly detailed prints.

As is typical for an LCD resin printer, the SL1 features a removable resin tank that uses a transparent FEP film as its bottom. Unique to the SL1 though, is how a motor gently tilts the vat after each layer change, thereby separating the print gently from the FEP film instead of lifting the print vertically and thus significantly reducing the tension exerted on the print inside the resin vat. By tilting the tank, the resin is also continuously stirred, improving the surface finish and overall quality of the print.

Beyond what’s under the hood, right off the bat, the printer’s build quality is noticeable. Especially when assembling the kit, you can see all the parts fitting together neatly; no need for jamming or bending parts into their designated place.

The Original Prusa SL1 boasts a rigid aluminum frame core, with a separate body. The sturdy Trinamic driver — battle-proven from the MK3 — ensures excellent z-axis stability and, with a weight of about 4 kg, the printer is neither too heavy nor too flimsy. When filled with toxic resin, a certain weight is exactly what one wants.

To minimize fumes inherent to the SLA process, the SL1 features a built-in high-quality carbon filter at the back. The fan’s casing can also be removed and mounted with a hose to channel them out the window.

When it comes to print area size, the Prusa SL1 offers a maximum of 120 x 68 x 150 mm, which is in the same ballpark as its budget competition and pretty standard on desktop LCD-based resin printers.

What does give the machine a premium feel, however, is the ease of operation. Gone are the days where you had to twist and turn a knob to scroll through the menu of a Prusa printer. For the SL1, Prusa ditches its distinctive click wheel knob and furnished it with a large color touchscreen that lets you tip-tap your way around the file directory in comfort. During prints, the UI provides you with an ample amount of information including the print time, the amount of resin used, and the total layer-height. You can even get a live visualization of each layer as it is printed.

Furthermore, the SL1 displays a level of thoughtfulness not present on many other machines of its stature. Take the manual fill level indicator, which serves as a maximum fill line and lets you top up without overfilling the vat. Similar helpfulness comes in the inbuilt resin sensor, which informs you if a print is likely to run out of resin mid-print.

All in all, the process of assembling was smooth sailing with only one major incident: connecting the WiFi cable to the circuit board (Chapter 4. /step 19. in the setup guide). Without being dramatic, getting the pinhead-sized connector to stick to the circuit board took us more than half an hour, a stark contrast to the one-click-and-be-done-with-it instruction. It also resulted in some anxiety when first turning on the printer, as circuit boards tend to be somewhat fragile, and any slip of the tools might lead to a premature end to the review.

Thankfully none of these worst-case scenarios happened. As a hint, off-record, to anyone having the kit in mind: Attach the WiFi cable to the circuit board before you screw it in. Then proceed as instructed. It might save you half an hour of frustration.

Apart from this minor hiccup, the setup was a stroll in the park.

Once the machine was assembled, plugged it in, and fired it up, we followed the setup wizard on the printers LCD display for the pre-flight check and calibration.

Prusa advertises the crucial step of calibrating the printer’s print platform and printing bed as being done automatically when, in truth, it should be called something along the lines of assisted calibration. Nevertheless, it’s an easy setup as — again — all instructions are presented not only in the manual but also on the printer’s LCD screen in the form of photographs and illustrations. The whole process takes less than 5 minutes, and once the machine is calibrated, it will stay calibrated for all consecutive prints.

After the assembly and pre-flight calibration are completed, it is finally time to start printing with the Prusa SL1.

As the Prusa SL1 is an open-source machine, you can use any brand of resin you like, as long as it is compatible with the 405 nm wavelength of UV light (the majority of desktop SLA printers are.) So, we tried out some third-party resins we had lying around from former reviews and, after tweaking with the exposure time, the results were also satisfying. In fact, with some trial and error on our part, SL1 performed admirably with a variety of materials.

A typical frustration with bottom-up resin printers such as the SL1 though is that you must wait for the print to run long enough for the print plate to clear the edge of the resin vat before you can see if it’s a success or failure. Especially as with resin printers the critical part of a print is the first couple of layers and if they adhere properly (particularly with third-party resin and changed exposure settings).

Woefully with the SL1, there is no way of taking a peek. While other resin printers allow for the print to be paused, automatically raising for you to take a look, this is unfortunately not possible with the SL1. Although you can pause the print, the plate stays put.

All in all, though, the outcome was satisfying. From the over one dozen prints we solidified during this review, only one print failed, sometime during a night shift, by what we assumed the next morning was a lack of support structures. A somewhat recurring problem we spotted, though, was that the raft beneath the support structures sometimes lost adhesion to the print bed at its fringes. While the prints still turned out flawlessly, and the problem had the handy side-effect of making it even easier to remove the print off the bed afterward, this is surely not the intention of the company.

In general, PrusaSlicer can automatically create an ample amount of support structures where needed, but sometimes it doesn’t hurt to add more manually just in case. This brings us directly to another key feature of the SL1 – the slicer.

The model context menu (right-click on a model) now lets you generate support blockers and enforcers. Support blockers are useful when you’re generally happy with the automatic supports, and you want to exclude some areas which either don’t need supports or might create hard to remove supports. Support enforcers work the opposite way. Turn automatic supports off and select specific parts of your model that will need supports.

Furthermore, the new PrusaSlicer supports material and printer settings for various resins, as well as a layer preview and object clipping.

As frequent Prusa-printer users ourselves, we always liked the company’s slicer for its ease of use. And with the update introducing the SL1 to the fold, it has streamlined its usability even further, including the necessary tools for successful SLA printing in a simplified UI.

But not quite all the crucial features. By default, all SLA prints are printed as a solid block, meaning there is no infill. Hollowing an object lets you use less resin, first of all, but also allows for stabler prints, as a lighter object also needs less support (so there is less chance of breaking off), and a less dense crosssection has an easier to break bond with the FEP film.

At the time of writing, PrusaSlicer does not feature 3D model hollowing, meaning you have to fall back on programs such as MeshMixer or Windows 3DBuilder. Prusa Research has announced it is looking to implement the feature soon.

Another thing we found to be inaccurate when using the slicer was the print time estimation for the SL1 printer. On average, the print took about half an hour longer than the PrusaSlicer calculated. This is obviously not a deal-breaker but can be irritating sometimes, especially when trying to fit prints into office hours.

Apart from that, the PrusaSlicer is a great tool and fulfills (almost) all the checkboxes needed for SLA printing. As Prusa is big about open source, we are confident that missing features will be incorporated rather quickly.

The machine itself is a plug and play and comes fully assembled, consisting of a large steel container with a cover that you need to fill with around two liters of IPA (not included). Inside the container, you’ll place a disk – from the looks of it printed on Prusa’s in-house MK3S farm – with a small magnet attached to make the disk spin and stir the IPA during the washing phase. The lid does feature a handy clip mechanism that fits the print plate, allowing you to wash and cure your prints upside down; especially useful when cleaning small and fragile prints you don’t want rattling around in the basket.

After washing your prints in the IPA bath and removing as much residue from the model as possible, you can take out the container, wash the model off with some water, and then place it on the rotating disk to start the drying and curing stages. The machine has another useful built-in sensor that automatically sets it to washing or curing, depending on if the container is placed inside or not. The standard time setting for each stage is about three minutes.

Two things we came across in our review:

The swirling mechanism, powered by magnets, hardly ever functioned as intended. The turbine you “install” at the bottom of your IPA bucket did not seems to be accelerated by the rotating disk under the basket. We tried to stir it in the right spot with a rod (you don’t want your hands to make contact with that IPA resin mixture) and got it working for a while. The rattling sound it makes when spinning is the indicator.

Since you constantly have to switch between washing and curing, and therefore have to take the basket in and out, the turbine never really stays in place. This might be resolved by simply adding a stronger magnet at the bottom of the turbine to help it take-off; or by adding a frame to the turbine to center it to its intended position.

Secondly – and this is a minor frustration – there is a somewhat unwieldy change between the different modes. If you want to just cure without the drying mode before, you have to click yourself through an unnecessary amount of settings, and vice versa.

Minor irritation at the workflow aside, CW1 still does offer good value for its money. Other, comparable, SLA post-processing machines tend to be in the same ballpark, price-wise, and only consist of a curing station.

The intention of simplifying the post-processing process and condensing all steps into one machine is exemplary, but – at least from our perspective – could be improved. When the turbine is not working, it’s basically just a bucket of IPA where you soak your print in. Obviously, this still works, but not as intended.

Overall it did shorten and simplify the post-processing tremendously, though.

Technical Specifications

Here are the technical specifications for the Original Prusa SL-1

GENERAL SPECIFICATIONS

• Technology: MSLA
• Type: Resin
• Year: 2019
• Assembly: Fully-assembled/kit
• Manufacturer: Prusa Research
• Country: Czech Republic

3D PRINTING SPECIFICATIONS

• Build Volume: 120 × 68 × 150 mm (4.7 × 2.6 × 5.9 in)
• Layer Height: 10+ microns (0.01 mm)
• Resolution: 2560×1440 pixels
• Printing Speed: 6 seconds per layer
• Bed-Leveling: Automatic
• Display: 5.5″ full-color touchscreen
• Connectivity: USB, Wi-Fi, Ethernet
• Built-in Camera: No
• Third-Party Materials: Yes
• Materials: 405 nm UV resin
• Recommended Slicer: PrusaSlicer
• Dimensions: 400 × 237 × 225 mm

Where to Buy

Source: https://all3dp.com/1/prusa-sl1-review-3d-printer-specs/