Best open source 3D printers 2021 (with links to designs)

Closest thing I've seen at a reasonable price point: https://docs.v1engineering.com/mpcnc/intro/

I have never used a multi-thousand dollars printer. I own a CR-10 and a Prusa i3 MK3S+ though.

The CR-10 is fun to tinker with. When everything is in place and the printer is properly tuned, it prints well. My main usage for it is less printing parts I care about and more tinkering and learning about the printer itself though, as it's not very reliable (some are, some aren't - I suspect it's cheap because of poor manufacturing and QC).

The Prusa, on the other hand, rarely requires any maintenance apart from the normal stuff -- checking belt tension, replacing nozzles, cleaning the print bed, etc, and with less frequency ensuring that all screws are tight and doing a bit more deep cleaning. That's it. It prints well every time. It's both a pleasure and a bore, since I can just send stuff to it and it will chug away without intervention.

Their support is stellar as well, and everything they do is open source. Most consumer printers you see around are considered i3 clones (from the original Prusa).

I don't know what a few extra thousand $s will give you. I imagine corporate-level support, etc. For the hobbyist, you can't go wrong with Prusa.

They are now taking pre-orders for a larger, CoreXY printer. I'm trying hard to justify not shelling out for one.

I've used some really low price printers, a prusa and then some 10k ultimaker S5 printer. The low price ones can be hit or miss and may require more maintenance every now and then. They might not print as well as a prusa. I've had a prusa for a good year so far and have had to do no maintenance on it. It's basically set and forget and it prints great everytime. The 10k ultimaker had a few extra features like a humidity controller spool holder (which I don't think did much) and some proprietary nozzles. The 10k printer is very much set and forget but it also can break and error out and you have no idea what is wrong. The proprietary nozzles are like $120 each. I'd say the 10k price tag isn't worth it. I've used it in a university environment and I'd rather the school bought 10 prusas than one 10k ultimaker. That way, we'd have more students using them.

Typically support and reliability.

I started on a FF Creator Pro clone, then added an Ender 3, then built (and heavily modified) a SecKit Tank.

I recommend people start with a simple off-the-shelf printer. (Ender 3 on the cheap end, Prusa on the expensive end).

Automatic bed leveling is a huge quality of life improvement IMO (Prusa comes with, can be added to others). Other factors are size, speed, and filament range (temperature range, part cooling, extruder and drive, dual extruders, enclosure, enclosure heating).

I’m a tinkerer and don’t mind modifying printers. If I’m printing a random ABS part, it’s still going on my first printer. If printing a large part, it can only go on the SecKit. For a random PLA part, it’s going on one of the Enders. If I need two filaments (at once), it can only go on the FF, etc.

If you don’t own a printer now, start with an Ender 3 and a PEI spring steel sheet or a Prusa. If you start with the Ender, I’d also add auto bed leveling early on.

If your usage indicates the need for a more expensive printer, it will reveal itself and by the time it does, you can keep the cheaper printer, sell it for 50%, or cannibalize it for parts.

I've used more expensive printers for work (primarily Zortrax), and have owned a cheap Tevo printer and currently own a Prusa. I'm fully of the opinion to just buy a Prusa. FFF/FDM printing is at such a point that there are few performance differences between printers other than speed unless you are printing more exotic materials. More expensive printers aren't any more reliable than the Prusa in my experience, and cheaper printers typically end up as projects to get them printing reliably and safely.