Attaching 3D printed parts together is something you’ll probably run into sooner rather than later if you’re 3D printing often.
A lot of the time its because elements are just too large to fit on a print bed, meaning you need to print a full model in segments. Other times, you may be printing an object which simply cannot be printed as a single 3D model.
However you’ve come across the issue of how to attach 3D printed parts, you’ll need to find a solution. And that solution can come in many forms, as there are a few tried and tested techniques when it comes to attaching 3D prints.
The best options for attaching 3D printed parts
There are two primary approaches when it comes to attaching 3D printed parts together, gluing and snap-fit. Let’s take a quick look at the two options, and then I’ll look at both methods in more detail.
Technique 1 – Gluing 3D printed parts together
Gluing 3D printed parts together is possibly the most common form of 3D model assembly. When done correctly, a glued 3D model can look very professional with very little evidence of the glue or seam.
Gluing involves a process similar to smoothing your 3D model, where you’ll spend the majority of your time preparing your model. Once you’ve spent some time prepping, you can then form a really strong, and almost seamless bond with the glue of your choice.
There are a variety of different methods to gluing your model together, which I’ll cover in more detail below.
Technique 2 – What is a 3D printed snap-fit?
If you are assembling a complex or move-able 3D object, then gluing just isn’t right. Instead you should look at printing a joint into your model. A joint will allow the model to join together without any outside influence such as gluing.
One of the most common form of 3D printed joints are snap-fits. These joints kind of do what they say on the tin. They snap together thanks to part of the joint being flexible. And once attached, they’re very sturdy and stable.
Essentially, one part of your 3D model will have a hook or rod built in. While the other part will have a hole or slot where the hook fits in to. You then snap them together to complete your object. The flexibility of the hook allows it to bend in to the join, while “snapping” in to place to lock the model together.
Let’s look at both methods in more detail, starting with the gluing technique.
Gluing your 3D printed parts
Gluing is one of the most accessible methods of 3D print assembly. And it can be one of the most effective. When done correctly, a glued 3D model can be sturdy for years, and it can be very hard to see the seam. But how do you achieve this level of finish?
Gluing step 1 – Prepping your 3D model
Gluing a 3D model is essentially the method of joining two parts together along a seam. Therefor that seam needs to be prepared correctly to allow the bond to be as strong as it possibly can.
As I mentioned in my overview above, prepping your model is very similar to smoothing. If you want to learn how to smooth your 3D model, read my complete guide to smoothing here.
The main difference for prepping a model for gluing rather than smoothing completely, is that you will want to stop part way through the full smoothing process.
Essentially you will want to use sand paper to rough up the areas which are going to be joined together, just like we do when smoothing. However, you will only want to sand the join with a fairly large grit sandpaper.
The idea is to create a visibly roughened area. This will allow the glue to bond to the surface better, in turn forming a much stronger bond.
Once you have sanded your edges, make sure you clean away any excess dust. You will want to make sure the edges are as clean as possible before applying the glue.
Gluing step 2 – Choosing a glue
There are a few different types of glue that you can choose from when it comes to gluing a 3D model together. One of the most accessible is superglue, and most 3D print materials such as PLA and ABS both adhere well to superglue.
If you are using a print material which has more flex to it such as TPE, you may want to look at a different adhesive.
Superglue
Superglue is a great choice of adhesive for assembling 3D printed parts for many reasons. It’s easy to use, cures quickly, drys clear and most people have it in the house already. If you don’t, it can be very cheap to pick up.
For those reasons it is one of the most popular adhesives within the community. As I mentioned, many materials lend bond well with superglue, ABS, PLA and PETG to name a few.
When using superglue, you should absolutely stick to my prep technique above. Use a medium-large grit sandpaper to rough up your edges. You can always use a finer grit if you find the edges appear too rough. Remember, you just want enough roughness to allow the glue to grip.
Once you’ve finished sanding, ensure you fully clean the surfaces and clean away any dust or dirt. You can do this with a rubbing alcohol such as isopropyl. Make sure you let the areas dry fully before applying any glue.
Top tip: Use disposable gloves when applying superglue as it is extremely fast curing. If you get any on your hands you could easily become a little unstuck (pun intended!).
Solvent
Rather than using glue to attach your 3D printed parts, you can actually fuse them together by slightly melting them. This may sound counter-intuitive, however if you use just the right amount of solvent, you can create a strong and invisible seam.
The best part about using solvent as a bonding method, is that once your 3D print is bonded together there is absolutely no glue left behind. All you have is your 3D printed parts, and a very tidy seam.
Solvent, such as Acetone, works by ever so slightly melting the edges of your parts. Then while in a melted state, you hold your parts together, clamping them for a few hours or over night. Once the plastic has hardened, the two parts will have bonded together.
Solvent is a great technique to use on ABS, and some PLA materials as well. It could be well worth experimenting with this method if you are becoming tired of sanding away excess glue.
Top tip: Apply using a natural brush for more control over your placement. If your parts don’t sit flush together, you can mix some excess filament to your acetone to create a thicker texture. This will allow you to essentially mold your solvent solution to fill any gaps.
Heat
Using a similar technique to solvent above, you can use heat on its own to create a bond. This method involves absolute precision as you will be using a heat gun or soldering iron to slightly melt part of your 3D printed part.
It can be tricky with heat, to direct it to the area you intend, so I would recommend trying both methods above before moving onto heat.
However, if you fancy giving this a go, it can be very effective. Similar to acetone, you wont get any residue or third party substance left on your parts after bonding. so you can create a seamless bond if done correctly.
The method involves directing heat using a soldering iron, or a hot air gun to the edges of your parts. And then as the parts start to harden, hold them together with a clamp, and they will form a good bond.
Top tip: Speed is crucial with this method, as you will need to heat all edges that will form a bond evenly. This can be hard because as soon as you remove the heat source the part will start to harden.
3D Printing Pen
Another technique of forming a bond is using a 3D printed pen. This is a good technique to add to the list if you don’t want a visible bond to show. By using the same colour and material as your 3D printed parts, you can create a completely seamless bond.
Essentially, this method involves you drawing along your edge line in the same material used to print your parts. And then fixing your 3D printed parts together for a few hours while the new filament hardens.
You can achieve some very good results using this method, however the bond generally isn’t as strong as using glue or solvent.
Top tip: Only use this technique on decorative or non functional models, as the bond can break away over time. Match the material colour to create an almost seamless bond. And ensure you clean your edges thoroughly before applying for maximum strength!
Epoxy
Using epoxy to bond together parts is another efficient method, and is very similar to using any form of glue. Epoxy is extremely strong once cured, meaning your bond should hold up very well.
It can also be used as a filler, similar to the method I mentioned above with solvent. So if your edges aren’t a perfect match, epoxy can sit in any gaps that appear.
The main downside of using epoxy is that it requires much more preparation than using other forms of glue. Generally epoxy comes in two tubes, which then need to be combined to form the final epoxy.
One of the benefits is that you can get some extremely quick curing epoxy, minimising your clamping time.
Top tip: If you melt down and mix in some filament, into your epoxy, you can create a filler material allowing you to fill any uneven surfaces.
Printing 3D joints and snap-fits
Designing your models with an in-built joint is one of my favourite ways to create larger, more complex 3D prints. It allows for moving mechanisms, and it looks extremely mechanical and interesting.
If you design the joints in the correct way, they can provide both flexibility and strength to your model.
It is also a fantastic way to save time assembling your model. Just think, gone are all of those hours of preparing your edges, gluing, clamping, curing and finishing your edge. All of that assembly can take up to 24 hours! And most of that time vanishes when using snap-fit joints.
If you are printing multiples of the same object, either for manufacturing or retail purposes. That time can quickly add up!
Can you use any material for 3D printed joints?
You can use almost any method of 3D printing to create snap-fit joints. This includes all popular methods such as FDM, SLA and SLS. However your mileage, strength and accuracy may differ depending on your method.
FDM printed joints
As we know, FDM printing is less accurate than both SLA and SLS, but is much more accessible. You can still print snap-fit joints with FDM, however using regular PLA might not be the best material choice.
You should look to opt for a more stress resistant material like ABS, as this will hold up much better under the strain of movement.
SLA printed joints
An SLA 3D printer will produce a much more accurate fit when it comes to printing joints. However, the resin itself isn’t designed to be repeatedly moved, meaning it isn’t the strongest. You can get specific durable SLA resin which will fair much better than regular resin.
SLS printed joints
SLS printing is similar in many ways to SLA. They both use a laser to essentially build your 3D print. However the material is much different. An SLA 3D printer uses liquid resign, which hardens under the laser. And a SLS 3D printer uses powder which is fused together.
The latter is more costly to produce, but is great to prototype strong 3D printed joints. SLS 3D printing is my preferred method of printing snap-fit joints which are designed to last.
Top tip: You can always use the other methods to quickly prototype your joints, before committing to the costlier SLS method. SLS nylon is a fantastic choice for printing joints.
The two main types of snap-fit
There are multiple types of snap-fit joints, however there are two which are much more common place than others. They are cantilever and annular snap-fits.
Cantilever snap-fits
Cantilever is by far the most common form of snap-fit joint, and works in a very similar fashion that I mentioned at the top of this guide. One part will have a hook, and the other part will have a slot for that hook to snap into.
You connect the two by pushing the hook into the slot or cut-out and it will “snap” in to place. The two elements will lock together forming a strong join.
Annular snap-fits
When thinking about annular snap-fits, think about a pen cap, or a push-pull bottle cap. With annular joints, you can push one part of your model over the other forming a seal. This seal can be waterproof.
The method can only be applied to circular parts, and uses grooves on both parts. You build in a groove into your main 3D printed part, and then the exact same groove but inverted into your secondary part.
As you push the parts together, the grooves will interlock forming your seal. Annular joints are much more specialist and have much fewer applications.
How to design and implement snap-fits
Now we’ve run through exactly how snap-fits work, lets look at a few top tips on how to design strong and sturdy snap-fits.
The most important things to remember when designing snap-fits is to ensure you create a strong joint. One which will last multiple uses and wont bend or snap under stress.
To achieve this, you need to design your joint correctly. Ensure that your joint fits flush with your slot once attached, and that the joint isn’t in a constant state of stress. Meaning your snap-fit should return to its original position once attached, and shouldn’t remain bent or distorted while in position.
You can also look to widen your joint itself to distribute the stress better. Widening your joint isn’t always possible, but I’d recommend doing so if your design allows for it.
Also look to fillet your corners. Filleting any corner, especially at the base of your cantilever, distributes stress much better than a harsh 90 degree corner.
Look to implement an easy method of removal if your planning on using your joint often. You can implement holes allowing you to push your hook away from the build when disassembling.
Finally, try to build your cantilever in the correct direction. Building it vertically will inherently weaken your part due to the way that anisotropic method that 3D prints construct objects. Try to print your cantilever horizontally where possible.
Conclusion
Designing 3D printed parts to be joined shouldn’t ever be a tricky task. There are a multitude of ways to bond together multiple parts effectively, both to form a solid object, and a move-able joint.
Hopefully the guide above will help alleviate any potential stress that you may have with assembly. And provide you with a few techniques to experiment with. Happy 3D printing!
