Basics: How to post-process your 3D prints!

A few simple steps can turn your 3D prints into something useful and special!

When 3D prints come off the printer, more often than not, they are not really finished yet. So here are a few things that you can do to get your 3D printed parts looking and working even better.

AprintaPro reached out to me for this sponsored videos series to be featured on their PrintaGuide platform, home to 3D printing tips, tricks and guides. Check out AprintaPro and the PrintaGuide site at the links in the video description below!

Before we start, a few safety tips: When using a knife or other sharp object, always cut away from your body and any fingers you’ve got holding the part. Yes, that’s going to make gripping the part a bit harder, but it’s better than slicing off a fingertip. Use a vice to get the part held in place properly. Also a good idea: Gloves with a bit of resistance to getting poked and some safety glasses against bits that might fly off..

Next up, chemicals, we are going to cover some solvents like acetone, and while these aren’t super toxic, you should still take care not to get them on your skin or breathe the vapors. Most of them are also flammable.

What’s definitely no joke, is epoxy – while it’s a very common structural adhesive, if it gets on your skin or you breathe dust from sanding it, it can quite easily sensitize your immune system to the resin and hardener. And after that, good luck ever using epoxy again when you end up with an allergic reaction every time. So make sure you don’t let it come to that, wear gloves when handling uncured epoxy, a respirator when sanding it and just avoid any exposure. It’s really easy to do and it can save you a lot of headache – literally – for the rest of your life.

So starting with the part right off the printer, the first thing i’ll often do is just to give that area where the print made contact with the build plate a bit of attention. If you’ve set the zero position a bit too low on your machine, for example to get a bit extra adhesion, you will end up with a this tiny lip or burr on the bottom of your part. This lip can end up quite sharp and, most importantly, keep your parts from fitting well together. Or you might have used the brim feature on purpose. What i’ve found to work really well with a bit of practice, and particularly for concave and inside parts of your print is just to grab a boxcutter and use the back of the blade to guide it around the contour. For convex shapes, this doesn’t work that well and while ABS and copolyesters cut really easily, if you are using a PLA that is particularly brittle, then cutting just won’t work at all. So for those, i simply grab a file and give them a quick pass. Protip: These small needle files always come in handy for finer details and aren’t even that expensive – links in the video description! When using files on PLA, always go a bit slower than you think, since PLA will easily turn into a gooey mess if you get it too hot.

Next up, functional geometry. Obviously, if a part doesn’t fit then you can always file them to size, and most 3D printed plastics can also be milled and sawed if you really have to. Drilling and reaming also works, but you shouldn’t just take a plain surface and make a through-hole or screw a wood screw into it when you don’t have the proper geometry in your file already. Not having the extra material from the extra walls will really limit how strong those connections are going to end up. What you can definitely do is using machine threads with your parts. First off, what a lot of people don’t realize is that you can actually tap printed parts and create reliable connections with that. Just give it bit more thread length to engage, about twice your screw’s diameter is a good start. You can find tables to the tap drill sizes online – just design those into your parts and you’ll be able to tap a good thread into it right away. As always, keep an eye on the heat you’re generating, as PLA and copolyesters can easily soften up and melt during tapping. If you’re not confident with plastic threads, you can also grab a few of these brass inserts and melt them into your part. Again, you should have a suitable bore in your printed part already and then you can simply grab a soldering iron, set it to a low temperature and press the insert into your part, preferably from the opposite side your screw will be pulling from.

So what if you’ve got multiple parts to join and don’t want to go with screws? Well, adhesives are always an option. So PLA and ABS-like filament are incredibly easy to adhere together. Pretty much anything works, including CA glue aka. superglue, Epoxy resin or contact cement. PET and Nylons are a bit trickier to adhere, and while many adhesives will sorta stick, they often don’t have the same strength as with other materials. For decorative purposes, it’s probably ok, but roughing up the surface with some medium grit sandpaper often helps as well. What you can also do for ABS and quite a few PLAs is solvent-welding the parts with acetone, as i show up here. That creates extremely strong bonds and you can even get specific welding agents for PET if you want to.

But what if you’re not going for mechanical parts? I know, sorry, i just have that engineering background and that’s sorta what i do, but there’s definitely potential for modelmaking and art pieces. By the way, if you want to get your mind blown on what you can do with 3D-printed and non-3D-printed models, check out Punished Prop’s channel, they’re pretty awesome.

So what to do to get 3D prints looking even better? Well, if you have the option, start with a finer print setting with lower layer heights, that’s going to save you a bunch of work already. Then i’d recommend giving your parts a light sanding, it doesn’t have to be perfect yet. Next up, if you have the option to vapor-smooth your part, that’s always a good idea and really simple to do as well. While you can get some nasty chemicals for PLA and PET, i’m not going to name or recommend those to you, but acetone for ABS, ASA, HIPS etc. always works.

So at this point, you either have a roughly sanded part or one that is already slightly smoothed. Let’s get that perfect. Almost all materials can be painted. Nylon, again, being the one that sorta sticks out, and PET won’t give the paint that much grip, but as long as you’re not hammering the part, you should still be ok. Starting with a filler/primer, the standard autoparts rattlecans are actually a pretty good choice here. After each filler pass, you should give it enough time to cure and then sand it down until you can see the base plastic poking through. Wet sanding is a good idea to help with cooling the surface and to a better surface finish. Repeat until satisfied and then move on to your regular painting process. If you’ve got larger blotches to cover up, or want to do a bit of sculpting, a two-part filler compound will give you a hand there as well, but as always, you will need to sand it down afterwards to get it perfect.

So if you do it right, you might just get yourself some parts that really don’t look like they were 3D printed at all, or, using the tips for mechanical parts, massively improve the usefulness of your prints!

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And that’s it for today, thanks for watching, and I’ll see you in the next one.

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