3d printing has been around since the 1980s, and since then there have been several technologies of 3d printing invented. For home use, though, the two main types of printer are FDM (where the hot nozzle deposits melted plastic filament to build a model) and SLA and DLP printers, that use liquid resin that cures with light (SLA printers use a laser to harden the layer of resin and DLP use a computer screen that shines UV light).
SLA and DLP 3d printers are as fast if not faster than FDM 3d printers, and have much higher quality. They currently suffer from smaller print volumes, and the plastic resin material is messy, unhealthy in the uncured state, and much more expensive than FDM printer filament.
3d printers of all types are becoming cheaper and better all the time. The level of detail achievable on printers today are much superior to what they were only a year ago, and next year we’ll look back and shake our heads at how far we’ve come. Not only are there new printers, but there are new processes that, up until a few years ago, would be prohibitively expensive and only found in the realm of research labs.
I had the typical geek “analysis-paralysis” of trying to decide when to buy a printer and start printing 3d models. What won the day for me was that the current printers are “good enough” for quality and the size of the print area for me to begin. I could wait until next year, and the build area will likely be twice as large in the X, Y and Z directions. I decided that the lessons learned by buying one now (which I could afford) was valuable. I can save for a new printer for next year, and I’ll be better armed with experience and knowledge of what to do and how to do it. So then it was on to which printer to buy, and my choices were SLA- or DLP-style printers. I needed to understand the difference and choose from there.
Stereolithography (SLA) Printers
Stereolithography (SLA) printers started being seen in the commercial market about five years ago, and are coming down in price. They are quite precise, and use a laser to harden ultraviolet (UV) sensitive liquid resin in a bath. Just as in fused deposition model (FDM) printers that add melted plastic from a spool, the SLA printer builds up its print, in layers, but out of a liquid resin bath. The 3d model, as it is being built, seems to emerge from the liquid resin bath, one layer at a time.
The layer heights from such printers can be very thin, as the printer aims light, rather than guides a nozzle, which can be done much more precisely. Many SLA printers can print at layer heights of 25 microns (or .025mm or .001 inch). Most FDM printers struggle to get to 100-micron layer heights, and 150 microns is more typical. As you can imagine, the models can be made with very smooth surfaces and fine details. For those that want to print figurines or small models with high detail, this is just what the doctor ordered.
The downsides, though, are price of the printer, price of the resin material, the speed of the print and the small print area. SLA printers can be quite expensive. They require that the laser light scan across the resin bath to harden the resin for each layer that’s printed. This can make it slow to get your print, but you’re going to love your print when you get it! The quality is very high! Resin can be up to $50 for a liter of liquid resin, and that will print even less than a kilogram roll of FDM filament plastic. The technology can be slow to print, having to scan across the resin bed for each layer, then do it again for the next. It has to hit the resin long enough for it to cure, so it can’t go as fast as possible. It’s constrained by that curing time for the resin (which is very fast, but not instant). Print areas are rather small for this sort of printer, too. You won’t be printing larger scale models or buildings, but you could print figurines up to 40mm scale or vehicles up to 20mm scale with high precision. For me, that’s right in line with what I’m printing. I can rely on a good quality FDM printer with a much larger print volume for larger terrain, buildings or scenery pieces.
The upside, of course, is quality. The prints look very close to the quality of plastic kits, without the mold lines! You may have small bumps or artifacts from where the supports connect to the model, but these are usually easily cleaned up after curing with some fine sand paper, emery board or fine model file. You can control where supports attach to a model, but I’m not yet sufficiently knowledgeable to know where I need a support or where I don’t, so I use the automated build support placement in the slicer and let it do its thing.
Digital Light Processing (DLP) Printers
And what about DLP printers? Technically, they’re a type of stereolithography printers. The printer type uses light to cure liquid resin that’s in a bath, creating layers one at a time. What makes this printer different is that the layer is printed all at the same time. Instead of using a laser to trace the layer and harden the resin, a computer screen is mounted below the resin bath. It is modified to shine UV light up into the bath. Only those pixels that conform to that slice of the model are lit.
Like the SLA printer, the main moving part for a DLP printer is the print bed, that moves up and down along the Z axis. So, like the SLA printer, the print looks upside down when printed, rising out of the resin bath as each layer is cured. The quality of the prints is excellent, but not quite as good as an SLA printer. This is due to the differences in technology. With an SLA printer, the laser’s path is smooth, making smooth hardened surfaces. With the DLP printer, the screen is lit with those pixels that correspond to the layer of the printing model. The screen pixels are square, so you’ve always got those “jaggies” on the surfaces. The jaggies are so small, though, that I can’t see any real-world jaggies on my models. It’s mostly theoretical of a disadvantage. Fun fact: a square pixel in 3d space (one pixel on the screen and one layer thickness high) is called a voxel – a 3d pixel!
Disadvantages or Drawbacks Common To Both SLA and DLP Printers
A major drawback of DLP and SLA printers is the mess involved. Liquid resin is wet, sticky and hazardous. You’ll use roll after roll of kitchen paper towel and Nitrile rubber gloves to combat the mess of spilled or dripped liquid, uncured resin. With a careful workload and the right tools handy, safety can be maintained without too much extra effort and you’ll keep you and your workspace healthy. If you have kids or pets, it’s best to put the printer in a closed space (with good ventilation) with covered garbage cans. You’ll generate garbage that has uncured resin in it or on it, so keeping it out of the reach of others is a good move.
Another drawback is the smell of the resin. It has a distinct, chemical smell that gives some people grief. For me, sitting in a room with the printer for an hour will give me a minor headache. That tells me that there’s something in the chemical not friendly to my sinuses. I get the same headache when I’m around people who vape, so maybe I’m just sensitive.
The smell is vaguely unpleasant, so having good ventilation in the room that you’re keeping the printer is a good idea. Where I live, it’s quite hot in the summer, so opening a window can be problematic. I used to live in Canada, and the winter there can have the same effect (for the opposite reason). Even a fan can help dissipate the fumes and keep the area more pleasant. You may have issues with your cohabitants, too, though. I keep my printer in a closed room so that the smell is contained within the room, but I’m sure that makes it worse in the room itself (unless I’ve got the window open). It’s a consideration, but not a deal-breaker for me.
SLA and DLP printers are such a step up in quality that I’m willing to live with the minor disadvantages that I’m currently experiencing. The toughest drawback is the small size of the print area with my AnyCubic Photon DLP printer. Newer models in the future will likely have much larger build volumes, and the resolution can only improve from here. I’m looking forward to a great future for my 3d printing, but honestly, my present is pretty darned good!
4K DLP Printers
4K DLP Printers refers to the resolution of the computer screen that allow UV light to shine up into the print resin vat. On most home printers, the X and Y axes have a resolution of around 47 microns. The Z axis, controlled by the elevating screw, can have higher resolutions and can achieve 25 microns. 4K computer screens will give an X and Y resolution around 10 microns. See the Phrozen Sonic Mini 4K Mono printer as an affordable example.
Laser SLA Printers
Lasers can have higher resolutions than computer screens, currently, in the technology to shine UV light into the print resin vat. Also, the beam is round, meaning that the edges of a print aren’t jaggy as DLP printers are (due to the fact that they’re shining light in patterns that are square pixels). For home use, I don’t see the difference. The price though, at 3-5 times, is a big difference, and the printer is slower than a DLP printer.
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