The first thing to note is that resin printers with good settings will produce better looking parts than FDM printers pretty much every time. Resin 3D printers use a different process than FDM printers that is simply able to produce smoother parts.
That said, sometimes you want to 3D print a large part that won’t fit on an affordable resin 3D printer, and the surface finish you can get on FDM printers is good enough. For cases like those, you’ll use a FDM 3D printer, and this guide will tell you what you need to know to do that as well as you possible. There are primarily four things you can do to make FDM parts look good: 1) level your print bed, 2) use high quality filament, 3) use the right print settings, and 4) upgrade your 3D printer.
Level your bed
A level bed is essential in 3D printing for a variety of reasons. Without a level bed, you may end up with Elephant’s foot (where the first layer is smooshed and fat). Future layers can also be a little smooshed and an unleveled bed can cause inconsistent extrusion throughout the print. How you level your bed depends on your 3D printer, but you want a first layer that looks like what you see above.
Use high-quality filament
Low quality filament mixes in copolymers and additives that cost less but result filament that strings, clogs, extrudes inconsistently, doesn’t adhere to the bed, and is just generally harder to print with. If your supplier makes filament without drying the resin first, or if they produce it with bad process settings, your prints will not turn out how you want them to. You may think you’re saving money by buying cheap filament, but once you consider the headaches, replacement parts, and failed prints, you will find out that cheap filament is actually very expensive. PLA filament is the easiest type of 3D printer filament to make high-quality prints.
Adjust printing settings
Tweaking your printing settings can have a big impact on the quality of your parts. Most imperfections can be eliminated by preventing oozing and stringing, lowering the layer height and line width, dialing in your support setting, using a cooling fan on full for PLA, and printing a little slower.
Preventing oozing and stringing is already covered thoroughly in this guide, so you should read that if you think oozing and stringing are your problem. You may also want to check out how to fix blobs and zits that leave ugly marks on your print.
Besides what’s covered in those two articles, you can improve a 3D prints appearance by lowering the layer height of your prints. Lowering the layer height will make the print take longer, but it will also decrease the visibility of layer lines. You can’t make the layer height too small though. Generally, your printer will start to have extrusion issues if the layer height is below ¼ of your nozzle’s diameter. This means that you shouldn’t go below 0.1mm layer height with a 0.4mm nozzle. For many printers, even 0.1mm is too small. Additionally, you can go down to about 1x the nozzle diameter (0.4mm for a 0.4mm nozzle) for the extrusion width (also called line width).
You can also dial in your support settings to minimize any scarring left behind after the support material is removed. In particular, you should dial in the support X/Y and Z distances. A good initial guess is an X/Y distance of 0.7mm and a Z distance of 0.1mm. Tree support will show less scaring as well, because it build straight off of the print bed without using the print as its base. Reorienting or redesigning the print so that support material is not required is a great idea when possible!
Printing slower can also help with quality. Many quality issues are related to print speed. The 3D printer has better extrusion control at lower print speeds, and slower printing gives layers enough time to cool before the next layer is added on top. Additionally, slowing the print speed reduces the dynamic response of the printer as it flings around the print head and print bed.
There are innumerable settings in slicers these days, and this is not an exhaustive list of settings options that are available to you. Also, the number of ways a print can fail is practically innumerable. You need to look at the issues you see in your 3D prints and find solutions that are specific to the problem you are facing.
Upgrade your 3D printer
The last option available to you is to upgrade your 3D printer. Upgrading a 3D printer is daunting to someone new to the hobby, but it actually extremely common. Stock 3D printers are often missing simple upgrades and fixes that were invented years ago, but never quite made it into cheaper 3D printer models.
For good looking parts, you are primarily interested in making your printer control extrusion extremely well, so the first things to consider upgrading are the extruder and the hot end. If your 3D printer does not have a dual gear extruder, I would recommend upgrading to that immediately. The extruder is usually the issue in inexpensive 3D printers. After that, you should consider upgrading the hot end to one that eliminates heat creep, provides sufficient heating (> 40W), and preferably makes it easy to replace the nozzle. Several hot ends from Slice Engineering or E3D fit the bill. Finally, in a hot end, you should find one with cooling ducts that hit the part from all sides. Otherwise, you'll see that one side of the print is droopy while the other looks great.
By following these steps, you can achieve high-quality 3D printed parts with few imperfections and a smooth surface finish. It may take some experimentation and fine-tuning to find the right settings and processes for your specific application, but the end result will be worth it.