3D Printing is something I do periodically. There are several forms of 3D Printing, and some include:

• Fused Deposition Modeling (FDM)
• Stereolithography (SLA)
• Selective Laser Sintering (SLS)

At present, I own a Prusa MK3S, an FDM 3D printer that specializes in plastic models. I've also used SLA and SLS printers in my various workplaces. I've also reviewed a few different printers and done product testing for several 3D printing companies. Not least are Stratasys, Prusa, and the new kid on the block (at the time of writing) Anker.

What's the difference between the various styles of 3D printers?

Fused Deposition Manufacturing (FDM) Printers:

For most hobbyists/home users, many will start with FDM printers, which use plastic filaments, melt them in the extruder, then squeeze it out the nozzle in precise places. These may be the most common printers for several reasons, such as:

• They're some of the cheapest printers to buy and run (although buying the cheapest printer isn't always the best choice)
• They have the best price-to-build-volume ratio. Most printers of this type (outside the designated "mini" models) can usually print any size/shape within a box of 200mm x 200mm x 250mm or something close to that. However, they of course, can go up from there.
• You can use a variety of different filament types:
  • PLA (Polylactic Acid): The "go to" filament choice for many hobbyists because it's so forgiving and let's face it, comparatively cheap to other types. It is also often derived from corn starch, so it's relatively more environmentally friendly, but that also means it's more susceptible to UV, water and other solvent damage. However, there's a lot of variants like PLA "meta", PLA +, PLA MATTE, PLA SILK and there's no consistent difference between brands. There's a lot of vague descriptions about how PLA+ has "superior mechanical properties" to basic PLA like strength, rigidity, and impact resistance, but independent studies seem to show contradictory results. Try some and find which filament type is right for your needs.
  • PETG (Polyethlyene Terepthalate, Glycol Modified): This is my preferred material, but not something I'd recommend to absolute beginners. Whatever improvement PLA+ has over PLA, this is basically a "step up" again... pretty much across every property... except one. Flexibility. The down side of PETG is that it's only slightly more UV stable than PLA variants, and it is harder to work with. In general, if you stray too far from the "sweet spot" near the recommended print settings, you'll have a lot of trouble. Also, if you use supports in your print, PETG is strong, so it's quite hard to remove. If you like PETG as much as I do, and use it for prints needing supports, I recommend that you consider using a dual extruder/multi-material printer where the supports aren't made of PETG... if at all possible.
  • ABS (Acetonitrile Butadiene Styrene): If you like Lego (or ever stepped on a block) you know ABS is strong stuff. Even stronger than PETG, chemically and heat stable, but emits some God-awful and toxic fumes when printing. This can be quite a challenging filament type to use, it's a high-temperature filament, which means warping and stringing is likely if you don't print in a very warm, stable environment (translation: use the heat bed, and an enclosure to slow the cooling process), cooling fans aren't recommended. When finished, some people use an acetone vapour bath (another toxic chemical) to improve the surfaces by melting off imperfections.
  • Nylon (a.k.a: Polyamide or "PA"): Extremely hard wearing, somewhat flexible, chemically stable, abrasion resistant, takes dye jobs easily, and has low-ish friction. This is an even higher temperature material than ABS. Which means all the same problems with warping and stringing and the remedies therein (enclosure, and slower cool down). However, there's another problem. Nylon absorbs water from the air.. and this can lead to poor print quality, with steam bubbles and uneven extrusions. I strongly encourage you to keep your filament in a sealed container with silica gel or other dessicant to slow this down, and even dry the filament in a dehydrator or oven overnight just prior to use. This is not a beginner material, but if you master it, it's an extremely useful material in all manner of moving parts. Often you'll find that Nylon is reinforced with carbon fibre or fibreglass for extra strength and flexibility. This is extremely popular in the FPV drone racing scene. (They crash a lot, and everyone loves tinkering and DIY designing improvements).
  • That's not all: There are a bunch of others, Thermoplastic Polyurethane (TPU) for extremely flexible "rubbery" applications, Acrylonitrile Styrene Acrylate (ASA) for outdoor applications, Polycarbonate (PC) for ultimate FDM printed strength, Carbon Fibre (CF) for excellent strength-to-weight ratio benefits, High Impact Polystyrene (HIPS) for situations where impacts are likely and since it dissolves in limonene, can be used as a dissolving support structure around moving parts that are "printed in place", and Polyvinyl Alcohol (PVA) for completely biodegradable applications and support structures. There are other filaments laced with everything from wood, sandstone, clay, graphene fibres for electrical conductivity, some contain metal dust for a metallic appearance, some are glow in the dark, and others are mixed some magnetic/ferrous materials so they are attracted to magnets..

Down sides of FDM printers:

• They are very slow, but they're getting faster.
• The "quality of finish" is often less smooth than SLA/SLS printers, but that's improving slowly too.
• Lack of detail, compared to the other two.
• Pretty much all the filaments are plastic or plastic-like, with all the limitations and environmental concerns that entails.
• You'll probably need to sand, or smooth surfaces out using filler, as it's never 100% perfect. So there's usually some extra work to do.

Stereolithography (SLA) Printers:

If you thought printing ABS was a stinky, fume ridden experience, then SLA printers can take that to a "whole new level". Because it's all resin based and don't believe every claim that a resin is "low odour" or "non-toxic". SLA printers use lasers to selectively cure a UV sensitive resin. It really is basically printing with an epoxy-like glue. SLA is often faster than FDM printing, and offers substantially better surface finish and detail in the completed prints, although it should be noted that in general, most SLA printers have a smaller build volume than FDM printers, and cost more to buy, and substantially more to print. Despite all this, they can be stronger than FDM prints, and amazingly detailed, which makes it extremely popular in the table top gaming circles, model builders, and general maker communities.

Expect to make a mess! Oh, and you'll need other devices beyond the printer!

Because you're using resins, sooner or later it's going to drip, get into placed that are difficult to clean (especially in cheaper SLA printers) and even once a job is finished printing, it's likely that you'll still need to stick the prints through a wash (to remove any unwanted resin) then cure it in a UV curing station to ensure complete hardening. Often these are additional devices that are not included with the printer, and while some cobble together DIY alternatives, buying a proper device can save time and effort, while improving the odds of success.

Even though the prints are extremely detailed, most SLA printers only do one colour. So many hobbyist SLA printer folks end up painting their prints by hand.

Selective Laser Sintering (SLS) Printers:

These also use lasers like the SLA printers, but instead of resin, they use powdered polymers (plastics) to melt the dust together. This is (usually) a much less fume-ridden experience, and any excess powder can be shaken/brushed off. This makes things like washing and curing stations like those needed with SLA printers unnecessary. However, these are the most expensive printers that are within the reach of small businesses and well-funded individuals. At the time of writing this, they start at around $7000 USD (for a DIY assemble yourself kit) and go up into the five and six figure price range very quickly... even for a build volume comparable to the typical hobbyist FDM range.

SLS printers can (at least from my experience) make some very strong parts. Even stronger than SLA, and much stronger than FDM, but since these devices are getting up into the realms of cutting-edge industrial 3D metal printers including Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) printers, which are incredibly useful, but way out of the price range of ordinary mortals.

Interestingly, at the time of writing this article, Boeing is currently 3D printing (with Titanium no less) key engine components in their 787 range, allowing them to construct parts with inbuilt cooling channels embedded into that could not be done any other way. Meanwhile the fuselage is PRINTED using carbon fibre tape, and wrapped in extremely precise ways to increase the strength while reducing overall weight... it's sort of a mix of FDM and SLA processes. Cool huh!