Upgrading from Prusa SL1 to SL1S

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 A while ago I bought a Prusa SL1 resin printer with a washing and curing unit called CW1, both from Prusa Research. They came as a bundle and while the price was significantly higher than existing cheap SLA printers from China, I bit the bullet and went ahead with a more expensive set that I thought it will be worth it. 

The printer I bought was a kit to be assembled and from the very beginning, I could see there were a lot of quality components and advanced features. All in all, I have used the printer only a fraction of what I use my FDM printers. The main reason being the messy process associated with resin, even if you have a cleaning and curing unit (that helps on that front). The smell of the resin is yet another detail I do not like, though it is not much worse than printing ABS.

But recently I had the opportunity to install an upgrade to my SL1 printer. I have heard of different manufacturers replacing color LCD screens with monochrome ones, that while maybe more expensive, did have a slightly higher resolution and better light transmissivity. So I was expecting the upgrade to be not more than replacing the LCD screen. 


I have been wrong before and I was wrong this time too: The upgrade kit came not only with a new bag of Haribo candy and a new LCD monochrome display but with a lot of other unexpected components such as:

  1. A new print platform (with angled sides on the top)
  2. A new tank with the FEP sheet already mounted 
  3. A new set of FEP sheets (as the new tank is slightly larger than the old one)
  4. A new electronic board (called boosted board, not related to skateboards though :-)
  5. A tiny PCB adaptor for the new display (scarily small pins)
  6. A set of Allen and Torx tools 
  7. A few printed parts for various purposes
  8. A new UV LED panel with a set of lenses
  9. A new brick-shape power supply
  10. A metal bracket for the new power jack and switch.


That was a lot more involved than I initially expected. And what was not visible was a new firmware that would change some of the features of the printer, making UV calibration a thing of the past.


The upgrade

It took me several hours to disassemble some parts of the printer to replace the required components. Luckily, I had built my printer from scratch and I was somehow familiar with the parts. A lot of parts need to be replaced, such as:
  1. The LCD display
  2. The UV light LED panel
  3. The resin VAT
  4. The print platform
  5. The built-in power supply
Some wires need to be added between the new boosted board and the main controller board. The new UV light panel reuses the existing power cable but it was a tight fit. There is a data cable going from the A64 main controller board to the boosted board, there is a plastic part that will fit into a pin header to help you connect the connector properly to the pin header. I managed to make this wrong, so there was a warning message during the upgrade that went away once I set it right. I guess the newer version of that plastic part will make my mistake not possible. 


The software upgrade was otherwise trouble-free and my printer seemed to be happy and ready to rock and roll. 

The first prints

Filling up the tank and firing the first print seemed like a simple task after all the rebuilding and software installed, and what is best, the file could be sent directly from PrusaSlicer software using the wifi connection. One of the benefits of the new firmware is that wifi worked ok in my office while it did not before (signal is so and so). No need to move the USB drive back and forth. 

It all started well, but then boom! some odd sound I was not familiar with occurred after a few layers and then it went away, back to the normal operating noises. I could not see whether it all was working ok or not, but eventually, I could see things were not working properly (it takes a while till you can start to see the partially-printed part as the vat walls block your view meanwhile, transparent walls vats anyone?). 


So it looks as if the print was peeling off in the front side of the platform, but on close inspection, there are a number of layers that are properly attached to the platform all around. It is only after a certain layer that things started to go wrong.

The problem and the solution

For those of you familiar with SLA printers but not familiar with Prusa SL1, it is important to note that SL1 has a rocking/tilting vat. What that means in the resin vat can be tilted horizontally to help to peel the printed layer from the FEP film on the bottom of the resin vat. The printer does that for every layer after it has been exposed to UV light and it raises the platform too. 

Think of it as two independent axes that work together after each layer has been exposed. It seems that at a certain layer, the proper "choreography" was not done properly between these two axes so the printed layers were bumping into the tilting base thus making the Z-axis motor lose steps and/or deviating the print platform from its calibrated position. From then on, the print only adhered to the part of the last layer that was close enough (the side closer to the back of the printer). 


I was using some alpha firmware so the initial fix was to use a custom tilting profile but the long-term fix will be present in the newer firmware that will be distributed once the product is out. My guess is that a slight change is made on how these upward and tilting movements are coordinated to avoided any crash at any layer. It was not a big deal as all this happened and was fixed during beta-testing.

Is it really that fast?

The name of the new printer (after the upgrade and also the new model being sold) is SL1S (where S stands for speed). After all the parts replaced from the original SL1, I expected an increase in the print speed, so the name suits it well.

And once I installed the proper printer profile on PrusaSlicer I could see the prints could go really fast compared to what I have seen before. I am using Prusa Orange Tough resin for my test parts. The 0.05 mm layer exposure time for the SL1 was 6 seconds and it is only 2 seconds for the SL1S. I have read that it can go as low as 1.3-1.4 seconds for transparent resins. 

It is also reported that a layer height of 0.3 mm is possible and that with the proper resin, a full-height print can be completed in less than 1 hour. Of course, the later lines will be very visible in that case, but it is really surprising. I am not printing at these layer heights but I can tell the printer is now 3 to 4 times faster than it was before so I am really impressed.

At the same time, a small increase in the output quality is achieved as the new display lets light go through better and has a slightly higher resolution than the old one.

Is it worth it?

If you own a Prusa SL1 that you built yourself, I can recommend you the upgrade. If you bought the printer assembled I am not so sure as the upgrade requires some skills on different fronts (mechanical, electrical, electronics, software, troubleshooting). 

At $399, the upgrade delivers a lot of new components to increase the printer performance. I do not think it is expensive but I know you can buy a couple of cheap SLA printers for that money too. I prefer not to, as I have no room nor need for more printers and I like the trouble-free print experience I already had with the SL1. Like a car, people not always are buying the cheapest option available and many find a more expensive item worth it if it delivers a higher performance and comfort level. 

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