Almost two years ago, the team at Elegoo very kindly sent me a review sample of the Neptune 4 Pro - at the time a recent, budget-friendly, medium specification FDM printer with a good build volume. After some promising initial tests making wargames terrain - some of it truly stunning - a whole lot of life got in the way, and that review got put off - and put off - and put off. Then, the problems started. Now I've got a halfway busted machine, burnt fingers and a broken heart. If you're considering getting your first FDM printer - any FDM printer - here's what I learned from my many, many mistakes.
To be clear, the Neptune 4 pro has produced plenty of great prints, including some wargames terrain still in use at my local games club. Right now it won't. I continue to tinker with it, hopelessly optimistic, like I'm stuck in a situationship with someone who keep promising me that this time, this time, they're really going to change.
I've spent somewhere close to half the machine's cost in replacement parts and extra gear, because I can't shake the hope that I'm just one part swap away from getting it all working again. This time! But if I had paid for the base unit, the amount of money I would have spent is pretty much equivalent to if I'd just bought some Warhammer terrain - maybe from a 3D print farm who actually know what they're doing.
The issues I'm having stem from some fundamental elements of FDM printing which I was completely ignorant of when I started using the machine. If you're a more experienced maker who has built a 3D printer from a kit, none of this will be surprising. For newer 3D printer users with machines with more autocalibration tools and locked-down subsystems, these may be fundamentals you don't ever have to engage with - until the day when something, inexplicably, goes wrong.
At their most basic, FDM printers feed plastic filament from a reel into an 'extruder' where it heats it up until it's soft, and is then deposited onto a build plate. On the Neptune 4 pro, the extruder can move up, down, and left to right, while the build plate moves backwards and forwards (making it a 'bed-slinger'). Between heat, plastic, and three dimensional motion, the machine builds up a 3D object layer by layer. From the very first benchmarking miniature, it's magic.
However, while the description above is true, it's also so simplified that it's fundamentally useless when something goes wrong. An FDM printer involves mechanical, electrical, digital, thermal, and chemical processes, and every one of them can fail or be misaligned. In my case, almost all of them have gone wrong at one point or another. Or at least I think they have, because working out what, specifically, is causing a problem is its own special hell.
Let's start with the most common problem - bed adhesion. The first layer of your print needs to stick to the print bed. If it doesn't, the model can come unstuck from the bed partway through, and you'll return to find miles and miles of plastic spaghetti instead of a finished print. Or worse, hot filament can stick to the outside of the print nozzle, which in turn traps every more hot filament, until you notice the gunky blob of death or something on your machine goes wrong. But what causes bed adhesion problems?
Most likely the nozzle is too far away from the bed, and the first layer of filament is already solid before it touches it so it can't be bond. That can be fixed by recalibrating the Z-offset, the distance between nozzle and print bed. But be careful not to set that too close, or you won't be able to get any filament out of the nozzle - heck, you could even carve a furrow into the top layer of the print bed if you really botch it. And while you're at it, make sure that the bed is completely level for a nice even surface, because one part of the bed may not be level with another. And make sure you heat everything up to operating temperature before you start, since materials expand and flex when heated!
There could be other problems too. If the bed is too cool, filament won't be able to melt onto it for a good grip. Or it could be warm enough, but the environment around it could be so cold that the filament cools rapidly and contracts unevenly, peeling up as it bends. The print bed might have residue from a previous print, which you need to clean off with IPA. Or perhaps the filament has absorbed moisture from the air - it might even have absorbed water while sitting in a warehouse! You need to bake your filament to dry it out, which requires a dedicated heater.
Or something could have broken. One failed print coated my print nozzle in an orb of plastic doom, which also fried something electrical, stopping my extruder from being able to detect how close it was to the build plate. That might have been the Z-sensor, but it could also have been the extruder's micro circuit board, or simply the wire between the two components, so rather than replace one piece at a time I ordered a whole new extruder. I kept the old one for spares.
That proved to be a good move. Some time later I wanted to swap out the nozzle to see if that would fix a problem. That requires the extruder to be powered on and heated up, since any cold plastic inside the nozzle makes it all but impossible to move - and I wanted to remove part of the casing to make it easier to get a wrench around the nozzle. Like an idiot, I attempted the disassembly while the extruder was powered on. There was a flash, a puff of smoke, and with that I burnt out both the extruder's circuit board and the cable connecting it to the motherboard.
That little balls-up came about because I had lost patience trying to troubleshoot another pernicious issue. Sooner or later into a print the filament would stop flowing, and the extruder gears would start to make a skipping noise, indicating that they were trying and failing to push the filament forward. And the fun part is that I don't know why.
Most likely I'm just getting clogs. Since FDM printers work by heating up cool plastic, every system has a place where hot and cold meet. Heat wants nothing more than to creep up into the cool parts of the system - but hot filament in a place that's supposed to be cool will deform and form little plugs in any available crevices, and those jam the feed. But other issues are possible, and even if clogs are the culprit, which cluster of mechanical, electrical, machine calibration, slicer file configuration, and filament properties are ultimately to blame?
An update - literally as I was putting this article into the website, I had a print that went perfectly with nary a clog in sight. My most recent changes? I opened up the casing of the extruder and dusted some tiny plastic dust out of the feeder gears; flipped a small plastic tube inside the extruder upside down because hey, maybe I'd flipped it the wrong way during some previous strip and rebuild; and left the build plate and nozzle to preheat for a very long time before starting the print. Then, forty-five minutes into the print time, this utterly perfect print popped right off the build plate, because the bed adhesion wasn't quite good enough. I can change her.
With these experiences, I clearly can't recommend the Neptune 4 Pro. However, I can't call this an expert review, since it's clear that I didn't know anywhere near enough about 3D printers when I started using it. Experienced 3D printer users should look elsewhere for an informed opinion. But if you're a novice like I was or an amateur like I now am, this is an experience you might have. The printer worked well to start with, so I had no reason to send it back to Elegoo. Then it stopped working well, and I'm still trying to work out why.
Really, the message I want to convey isn't specific to the Neptune 4 Pro, because the printer itself isn't the biggest problem here - my ignorance is. If you plan to get an FDM printer, and I mean any FDM printer, do your homework. Join the online community of people already using it, read the documentation, work out what other tools you'll need to troubleshoot it, and find a local makerspace with experienced 3D printer users who can help you put all that into practise.
Several professional terrain makers have told me that specific models will "simply work" right out of the box - and if Bambu wants to send me a P2S to test after they've read this diatribe against the whole concept of FDM printers, I will gladly try one. But having stared into the abyss as long as I have, I don't believe that any FDM printer will remain faultproof forever - some may just be easier to care for, and may go longer before they need TLC. They're marvellous, complicated machines. Expect them to behave accordingly.
If you're a miracle doctor who has had my exact problem with a Neptune 4, a relationship therapist who can tell me what's wrong with me, or simply want to share commiserations, come and join me in the Wargamer Discord community.