3D printers

I got pretty into 3D printing in 2022. Here are some things I've learned. Be aware that the industry moves very quickly, and this information is likely to go out of data within a few years. You'll see the word "fusion" a lot, but despite my earnest prayers it never means nuclear fusion.

3D printing methodologies

The printing techniques one is likely to see in personal use are almost all material extrusion (FDM) or vat polymerization (MSLA and DLP). There are numerous other methodologies (see this All3DP article), but these make up the vast majority of printers intended for the home. Sadly, all known methodologies are cursed.

• Fused Deposition Modeling printers push filament (usually thermoplastic) through a hot nozzle to melt it. It is then extruded, where it cools and solidifies. The nozzle is moved in the xy plane until a layer is completed, at which point it begins depositing the next layer. The printing proceeds from the bottom to the top of the model, with the bottom resting on the buildplate (which stays at the same height throughout, or moves down).
• Masked StereoLithogrAphy (sometimes just SLA) and Digital Light Processing printers shine light into a vat of photoactive resin (a photopolymer), using e.g. a laser or an array of LEDs. The original SLA traced each xy layer using a laser and mirrors. DLP likewise uses mirrors, but they form a mask allowing a plane to be drawn as a single unit. MSLA uses an LCD mask, eliminating the need for a mirror layer (the light is blocked wherever the mask is activated; where it gets through, it solidifies the resin). The light source is underneath the mask, which is underneath the vat. The printing proceeds from the bottom to the top of the model, with the bottom attached to the buildplate. This buildplate rises as printing continues, so the bottom of the model ends up the furthest away from the vat (and thus at the highest point of the print).

Note that in both methodologies, problems can arise when a layer occupies part of the xy plane unoccupied by the layer underneath it. In the FDM case, material extruded into such areas is likely to fall to a lower z coordinate. In the case of vat polymerization, if the area is similarly isolated in the xy plane (i.e. disconnected from all elements below it or at the same layer), the solidified material is unlikely to rise along with the rest of its layer, settling instead to the bottom of the vat.

Other methodologies include powder bed fusion (SLS, SLM, EBM, MJF), material jetting (including DOD), binder jetting, and direct energy deposition (LENS, EBAM). Some of these get pretty esoteric. Some of them are practically welding. LENS spot-fuses titanium alloy powder using a multi-kilowatt laser in an atmosphere of inert gas to build jet engine blades. It is not cheap even before one considers the logistics of ensuring a regular supply of bulk-tanked CGA-680 monatomic argon (and avoiding asphyxiation thereby).

Which one is right for me?

Honestly? None. No matter which type of printer you use, it's likely to be semi-regularly fucked. Accept that going in. Your choices are primarily FDM or MSLA. Well-known FDM options include Prusa, Ultimaker, Creality, Anycubic, and about four thousand other options, including the ultra-hip Voron (a kit-only design for which you spend a few weeks sourcing parts, then assemble over the course of several increasingly unhappy days). MSLA has only more recently arrived on the mass market, with Elegoo, Phrozen, Formlabs, and some of the FDM folks leading the way. You can acquire an entry-level FDM or MSLA printer for a few hundred dollars (FDM printers are now sometimes available at the $100 mark), with significant improvements available near $1000. At the professional level, choices begin at several thousand dollars, and go up pretty much without bound. I don't know anything about that world.

Larger build volumes are pretty much always more expensive than smaller build volumes.

Bed alignment is critical for both FDM and MSLA printing. It is ideal for the printer to sit on as even a surface as possible.

Selecting an FDM

The gold standard consumer FDM printer is pretty much the Prusa i3 MK3S+, currently available in a kit at $800 or assembled for $1100. When properly assembled, it's said to be pretty robust. Newer printers such as the Bambu X1 are bringing more advanced software solutions to bear, though their efficacy is not yet generally proven. The open source Voron design spares no expense in achieving the finest possible consumer FDM hardware solution...but millions of people print with cheap Creality Enders and Anycubic Cobras and are pleased with the results. Spending a few hundred dollars more can improve some quality-of-life issues, but it will not free you of the obligation of understanding how your printer works. You will have to perform some configuration and maintenance, you will have to diagnose some print failures, and you will suffer some printer downtime due to jams and upgrades.

Placing the extruded material in three dimensions requires moving along three axes. G-code is sent to the printer to specify this movement. Polar printers spin either the printbed or the extruder in a circle, using polar coordinates r, θ, and z. Cartesian printers use x, y, and z. In CoreXY, and Cartesian-XY printers the bed itself moves along the z axis. Cartesian-XZ printers ("bedslingers") are common, moving the print bed along the y axis. Delta printers use arms, but most rectilinear printers employ gantries to move the nozzle. Gantry implementations include v-slot extrusion, sliding rods, and linear rails. In a great simplification, linear rails moving a nozzle in the x and y dimensions while the print bed moves in the z dimension is pretty much optimal when done correctly, but e.g. gantry misalignment will ruin any system.

Some FDM printers come with an enclosure providing thermal isolation. This is pretty much necessary for reliably printing temperature-sensitive/odorous materials such as ABS, and can reduce noise. Printing your own enclosure is a non-trivial task (they're large), and printing one that looks and functions as well as the manufacturer's is generally difficult.

Assuming reasonable hotend movement, nozzle size defines your resolution. The nozzle is the most exterior part of the hotend. Hotends can be open source (e.g. the MK8 and E3D v6) or proprietary. You can assume you'll pay a heavy multiple for proprietary hotends, so open designs are desirable. The 0.4mm brass nozzle can be considered standard. Larger nozzles can print the same volume more quickly (assuming sufficient supply from the heating element), are less prone to jamming, and have fewer layers per unit height (possibly resulting in stronger prints). Smaller nozzles can achieve higher resolutions in all three dimensions. Nozzle material governs heat transfer and wear resistance, with the latter being particularly relevant for abrasive materials.

FIXME print bed FIXME hot end composition FIXME direct v bowden FIXME firmware FIXME automatic leveling

Filaments

Basic filaments (PLA and ABS especially) are cheap and come in a wide range of colors, and can be effectively printed using brass nozzles in standard hotends.

Selecting an MSLA

MSLA printers are great gifts for enemies, because they fail almost as often as FDM printers, but can also poison you. They're a lot like cigarettes in that way--the worst part is the cancer. Just lifting the top off an FDM printer fills the room with the baleful stink of modern technical death, materials not known at Creation diffusing through your body, binding to various activation sites, inviting proteins into strange and exotic configurations, heralding a death that leaves your corpse too toxic to be burnt. Hah, just kidding, they're fine!