Why Side Holes Fail in 3D Printed Parts

Added: 2026-05-31

[00:00:00]What's up, mold breakers? Today, we're going to be talking about how to do holes, but not just any holes, but holes that actually go into the side of any given 3D print. Because the rules for designing a hole going into the side of a print are different from if you were designing them going into the top of the print. As we all know, 3D prints are made up of a whole bunch of layers, and the way those layers interact with your features change how you wanted to design those features. So, let's just go ahead and dive right in. So, if you just have a standard part where you just have a hole straight into the side, the first thing you want to do is make sure you make the brick correctly. Make sure you round the vertical edges on all these sides. If this yellow brick is the the bed, we need to go ahead and round all of these corners right here. And then, of course, chamer the bottom. This eliminates any sort of overhang issues, any sort of elephant footing issues, and make sure that you have a nice crisp, perfect, high tolerance cube regardless of what you're doing. Okay, now that we've got that going, we go ahead and put the hole inside of there. Again, you're going to fill at the outer reg ridge of the hole in order to make sure that you don't have any bang bang scenarios. These are all the most basic rules of designing a 3D print. But now, let's get to the hole. As we said, the issues with designing holes into the side rather than ones that come in from the top are really about how you interact with the layer lines cuz you have the layers going straight across the hole like this, which means that you have two main problems. You have splitting that wants to happen straight out of the sides of the hole, which is something that you always want to try to avoid cuz you want your parts to be strong and reliable. We're going to design these so that there's no way they can possibly split out, but we'll get to that a little bit later on. The other issue that you have is the overhang on the top. The top of a circle is not a perfect overhang. You have basically a flat area where the slicer and the resolution that you're using will create a situation where the part basically kind of sags at the top and you end up with a hole that even though it was designed in CAD to be perfectly circular, ends up looking a little bit squashed. So, let's go ahead and just start with that overhang first because that's the simplest thing to fix and has a few of the simplest solutions about how to fix it. The very first thing that you could potentially do is just not print it in this orientation. Now, I don't mean go ahead and rotate the brick up like that. That would be silly. But you can get basically the same situation without having to worry about the s of the layer lines. Right now, it's printed like this. You certainly don't want to print it on its side. That's the same thing. You'll have the same problems.

[00:02:11]Upside down doesn't do anything. Putting it down like that doesn't do anything.

[00:02:14]But what if you went ahead and took it and printed it at a diagonal? This is something that is really, really useful because you might notice that on this brick, you have a bed surface and then all of the other surfaces and a top surface. So you have two faces that look completely different from the other sides. But if you go ahead and angle it just like this, then you can now get this hole much crisper than it would have normally been. You can see right here, this is oriented like this. This was printed like this. But now side by side, you have a much crisper, rounder hole. Why was this? because we gave the bottom chamfer a 2mm chamfer so that you have enough contact area with the print bed. Put it right there and then designed a support rib underneath it right here. Now, the support rib has two small tiny tines which ultimately can be cut off with flesh cutters and that kind of stuff if you're really processing quickly. You can also make them smaller, but that holds it up so that it can be printed just like this. And now, not only do you have a crisper hole because at this angle, you don't have a sag anymore because there's no overhangs inside of there, like when it's printed like this, you also get a stronger hole because since the layer lines are going like this, they're effectively looping around the hole every time. So now you don't have a situation where you're splitting through the layer lines. you have a situation where you have to split through an actual solid loop which is almost impossible especially compared to something like injection molding. You get a part that is just as strong as molding because you have solid monolithic features around it. Okay. Now designing this actual rib the main thing with that is make it pretty darn thin.

[00:03:38]Write one I made this one about a millimeter wide and then you make those tines about a half a millimeter in direct in any direction. That makes them pretty easy to remove and you can do some other things to make them more invisible. Right here I just designed them as is. We've got another video where you can learn about grip fins and that'll show you how to design these way more effectively. The last thing is we actually made a round base for it so that it sticks to the print bed. You want a nice simple first layer whenever you're designing a first layer. So ultimately you end up with a brick like this that prints like that. And now you get a really strong hole that's really crisp. And that's the very simplest solution of solving it. Good. Done.

[00:04:12]We're totally finished here. Well, actually we've got a few more versions of these here. Um sometimes you cannot change the orientation. you just have a hole in the side of the part and it can't be printed at an angle or something like that. So, what you need to do is just compensate for that. So, if we're looking at the overhang on top first, let's just go ahead and look at the very simplest solution, which is to just compensate for that a little bit.

[00:04:32]This is basically drawing another circle on top of the main hole and extruding that. So, you cut it up a little bit so that it has a little bit of a roof. That creates the compensation that you generally are sort of looking for and that creates a rounder hole. But now you're dealing with tolerances and material settings and we don't want to deal with that. You never want to deal with material settings or the specific printer that you're doing. You want to design a part that can be printed anywhere. This is why it's so important to learn how to design for 3D printing.

[00:04:57]But with all the things that we can show you in this video, you can design a part that will print on any machine at any resolution in any material and will still come out well and reliably. So that's what we're going for here because then you can upload it to a service like Teleport. Teleport is our 3D print on demand service that connects directly into your Etsy store. When you get an order, a thousand 3D printers will fire up automatically to print that item, process that item, and ship it straight to your customer for you. This means that you get a thousand machines on tap for your business. No more changing filament out in the middle of the night.

[00:05:28]No more figuring out what the latest machines are. All you have to do is design a really good part, upload it, and then when you get an order, it is printed and shipped directly to your customer for you so that you can focus on designing more good parts and taking care of your customers and not worrying about how to run a factory on. in addition to running your regular business. So check out teleport today over at slant3d.com. All right, so that compensates for the top, but that's not a very good way of compensating for the top. There is a really common way that people teach, which are just this little point where you literally put a roof on top of it all. And when you look at it like this, you get something that's pretty darn good and decent and reliable. But the way you design this is you just have two tangential lines on the circle and then you have them intersect at the top. And wherever that is that makes you feel comfortable, that's fine. Literally all you're doing is changing a round filleted space into a chamfer. This is an excellent demonstration of why we use uh chamfers rather than fillets because you have a nice gradual layer line coming up there to where no there are no actual overhangs. But the problem with this is that you've just created a lot of slop in your hole to where whatever rod you stick into there can go back and forth however you want to. It's just not a very reliable or a very high precision way of doing this. So, I'm not a big fan of it personally. A much better way is to literally just get away from the round holes. The problem with this is that the round hole is segant. Why do you have to use a round hole? Nobody said that holes had to be round. You can do whatever you want to with them. They can be whatever you happen to be looking for. So why not just go hexagonal? What does a hole need to do? Well, it needs to have the threads inside of it so that you can bind with it and then you can move on with life from there. Those are all the things that you have to worry about. That's all there is. But if you are designing just a standard hole there, then why not just have the roofs be everywhere. Now with a hexagonal hole, you have no overhang, straight edges. And if you design it to be circumscribed, the inner part of this is binding with the screw if you have something that bites into the actual filament itself. So when it's printed like this, you end up with a really reasonable hole, but then you also have relief features in it. So as the screw is binding into it, it doesn't have to spread the hole out. any excess material that it grinds off of these faces that it's interfacing with can then fall into the corners. So, you can get a really good bind, but not so tight that you're now splitting out the outer layers. This is a really good way of designing a part without creating any sort of situations where you build up so much stress that it wants to split. Cuz if you put a screw into the circular hole, it is definitely pressing outward on that. But if you do this, then it's only pressing out into the materials that it's biting into. And that reduces a lot of the internal stresses while still allowing the hold of the screw to bind reliably.

[00:08:02]But say you don't want to use hexagonal holes. You need a perfectly circular hole, but you want to make sure that it has a little bit of room to give so that you can have a high tolerance uh friction fit hole and you don't want to have to worry about splitting out.

[00:08:13]Because again, whenever you have these layer lines going across here, those layer lines want to split. Well, what you can do is have a vertical relief here. What this does is it allows the hole to spread sideways so that it doesn't build up the stress to where it'll split wherever it gives, which is along the layer lines. So, these two vertical slots do two things. They get rid of the internal stresses so that this whole thing is a little bit compliant and will press outwards so that your screw can go and fit inside there or your rod or whatever it happens to be. And they also get rid of that overhang cuz we have effectively cut off this area that was sagging and given it an overhang. You can make this slot pretty darn small. You can technically make it like 02 mm if you want to. It could be almost invisible. In fact, you could actually place it behind the wall here so that the main body of the hole is looks like a regular hole, but behind it is this slot so that it's completely covered over right there. But ultimately, it's just a way to give some leverage to the screw so that it can spread that wall those walls apart if it needs to get inside of there. Okay. But these top slot features have another feature. If you're designing a threaded side hole, well, the threads are going to sag and you're going to have all the problems of a standard round hole. But if you take the threads and then just cut out the top and the bottom, you eliminate that entire seging problem, but you still have the threads on the side. So you have a part that is high precision and you have high precision threaded parts inside of there that will be able to screw together reliably, but you eliminate the seging at the top that would mess with your dimensions. Many people will leave threads just generically there, but then you have the seg that changes how your parts bind and that kind of thing. Whereas if you just cut out the top and cut out the bottom, technically just the top, but the bottom eliminates retraction and other sorts of problems. So it just cleans it up. But if you cut those both out, then you have only the side features, which are limited by the size of your nozzle. Like you can only make threads that are 4 mm thick, which means that you're pretty darn chunky at that point. But when designing those side threads, you can do it, and then you can move into there.

[00:10:02]The other option is is if you need threads, but you don't want to just bite directly into your 3D print, but you want the threads to have purchase, you can apply a little bit of texture or just small ripples there on the inside so that the tiny threads like an M3 nut threads have something to bind into.

[00:10:17]They have hills and valleys that'll get into their threads, but they do not create uh the same precision as actual modeled threads inside of there. You're just creating roughness so that there's more material for the threads to bite into. Those are ways of dealing with super small threads and then large threads that are up to point4 mm in size cuz that's the size of a nozzle. Just cut out the top and the bottom and that eliminates any sort of precision problems that you have. But what if we just need it to be stronger? We want something that will last for a long time outside where heat freezing and cooling and small continuous cyclical stresses are going to be interacting with this part. It's going to end up splitting along the layer lines. If you have it loaded at all inside of there, the layer lines will eventually fatigue and then cause failure straight along there. So, how do you reinforce this hole and make it so strong around the outer edges and along these layer lines that they don't actually cause any sorts of issues?

[00:11:07]Well, the very simplest way are micro features. Micro features are very small cuts or holes or something else that you would put into the part. Right here, I designed a hexagon around the outer part of the hole. And in this case, I made it 0 2 wide. This is literally dependent upon the slicer that you're using. Most slicers will close gaps that are 0.05 mm in width. They basically fix that inside of the SDL and just close them.

[00:11:30]That's like the default inside of Orca Slicer. But again, you want the slicer independent. So generally you want to go up to 0.1 maybe even 2 mm for these sorts of micro features to make sure that they actually appear when the part is sliced because they can be closed by STL fixers, all kinds of things. But you make them large enough to where they're present but small enough to where they basically don't create other sorts of problems. This very first version is basically just putting walls on the outer side of the hole. So this is inducing more walls around the hole.

[00:11:57]Plus, it creates a secondary protection cuz if there is a split outside of the hole, well, it will only go to this outer edge and then it'll stop. Now, that will release the tightness of the screw so that maybe it could rattle out or something, but it doesn't have catastrophic failure. It will not run all the way through your part and cause the entire part to split off like you're putting wedges into a piece of wood. But this is a very simple extrusion. You can take it the full length of the hole if you want to, but I don't recommend it. I mainly recommend just on the outside because again, it's a starting point and it's a control point so that you know where the fractures will happen. It will happen right there, but it'll never go any further. Cuz if a fracture does happen right there with these thickened walls, you can move it out. One addition that I would make even to this design is I would actually move it out almost 2 mm away because the vast majority of walls are 1 millm thick. So you can go double distance away and instead put this slot out 2 mm away from the hole and then you have maximum amount of walls around the part in order to hold it together. Now there are multiple ways of doing these sorts of micro features based on what you're trying to do. Another simple way is to just do circular holes around the outside. And we'll actually probably pull up the CAD here so that you can see what this looks like. But you can see just those little divots, just those little holes right there. These are all inducing walls around the part. And again, probably should have brought them out a little bit further so that you have the walls into the hole as well.

[00:13:11]But again, it depends on what you want because now we have solid walls coming out all the way to here, 1 millm from the outer part of these small holes. So these micro features induce the slicer to place walls where you otherwise wouldn't. That means you can put strength around certain areas that you otherwise wouldn't have if you were just using default slicer settings. This prevents you from having to do something silly like say, "Oh, I need six walls or something like that." No, you can just upload this to any slicer and your part will come out strong and reliable, which is a super useful skill to have because then it can be manufactured and made at any time, anywhere. You can share files and people can make sure that it prints reliably and you're not communicating 3MFS between one different proprietary system or another. So, these types of micro features can be really useful. But ultimately, what you want to do is you're just trying to prevent it from splitting along these layer lines, right? Well, if you split along these layer lines, then why not just reinforce straight here along the plane where it's going to split? Well, that's what we went ahead and did here. Right here, you can see we get to the thickness out to about here, which is pretty darn good, and you have some redundancy, but why not just prevent it from ever splitting?

[00:14:11]Just make that part stronger. So, what we did was go ahead and just add a solid plane straight across here and straight across there. And that ensures that you can't split along this place where it wants to split. You reinforce it as far as it can possibly go. But there's a trick to this. If you do this by using micro features, you're cutting a slot into this part. Right here, I've got a 2 mm plane that you can just barely see those two little lines that I tried to make it more prevalent for you for cuz it was actually invisible the first time we did it. But these two little lines, I filled it out so that they kind of show up. But you can see that they're below center. If you put them dead center, if you put a plane straight through dead center, then it could be the zipper. it might not fully adhere together and then you can end up with a zipper straight across your reinforcing feature which isn't very useful. But if you go ahead and put it down a little bit low and then cut that plane through at an angle like this, now you have much of the same reinforcing function, but there's no way for it to go fully through it all the way and have it serve as a zipper cuz it's operating on different layers. So angling it like this makes sure there's no way for it to fully split through the whole thing. gives it much more reinforcement all on all sides of the hole and creates a more reliable feature. And of course with all of these, I made this visible so that you can see where the origin was, but it's probably better to take a look at it inside of the CAD, but you can put it behind this front face so that all of these micro features that we've talked about are just invisible and just exist right behind the front face of the part.

[00:15:32]So they don't have to cut out through the part, obviously, but this is an excellent way of reinforcing stress concentrations completely in a way to where they can never really break at all. This is all great, but what if we want a hole to actually vary in size? 3D printing can sometimes have kind of lower tolerances to where if you want a really really high precision fit and a perfect friction fit every single time, regardless of material and regardless of machine or resolution, then what you want to do is have this part be very, very blatantly compliant. Of course, we showed you all the slots and those kind of things to have the part adjust and move and grow and shift, these types of things to where the screw can bite into it or the hole can spread a little bit so that the screw can get in there. But if you really want a good precision fit and a very specific sort of tightness, maybe it's something that you want to go in and out of a bunch of times, then you'll want to design compliant features. Grip fins. Now, grip fins we've all talked about before, but they've always been about holes in the top of the part. But looking here at the side, this is how you design grip fins here. It's pretty much the same. A grip fin has to flex along the layer lines of the part. So here, literally what you all do is you just design the hole and then you do cutouts on either side of it that create these two fins, these two flange points that are now able to flex back and forth just a little bit. And you can see that motion right there.

[00:16:45]They have a spacing of 2 mm on the top and on the bottom. That way they can break free. And I put about a millimeter of space behind them, but it all depends on how hard you want them to bite. In order to make them bite harder, you make these fins thicker on the outside or you can make them shorter. Both of those will work. In this case, I made them about half the distance of the hole. So, going down here about this far. And actually, I should be hold showing it to you like that. These fins give you the ability to make a hole that adjusts in size so that if you want a particular fit over a long period of time, you have a hole that's never a friction fit or never too loose. It always holds it at a constant pressure as you're going in and out of it. But this also serves as a way again of protecting fracturing because now you're not creating high amounts of stress inside of here and split along these outer layers is not a big of an issue. And this creates something that is very compliant, very reliable. And then you can put a screw in there to hold it, or you can have other sorts of functions and features if you're wanting to plug together. These can act as snap fits. They can do all kinds of things.

[00:17:40]So that is how you design holes that are going into the side of a part. Again, with 3D printing, you have a nonisotropic piece. The top is different from the bottom is different from the side because you have different dynamics. And while you can slant them in order to make it kind of holistic throughout the entire part, the main thing you need to be aware of is where is the stress? Where is it going to want to split? And then you can reinforce those areas or introduce compliant features so that that stress is relieved. Those are the biggest things to do. But with designing holes in the side, you just want to be aware of how the process works so that you can design for that process and get exactly the results you want every time you're designing here. So this is how you do holes. Hope you enjoyed. Like and subscribe down below and check out our other videos about how to design these sorts of features. And of course, if you're looking to start up a 3D printing business or making 3D printing products, I recommend checking out Teleport over at slant3d.com.

[00:18:31]Have a great day, everybody.