How to 3D Print Connecting Joints & Interlocking Parts
3D printed parts can be improved by using connecting joints & interlocking parts within the design, but they can be tricky to 3D print dimensionally. After having some failures with 3D printing these parts, I decided to write an article on how to 3D print them correctly.
To 3D print connection joints & interlocking parts, you should ensure your printer is calibrated properly so it isn’t under or over extruding, allowing for better dimensional accuracy. You want to leave an appropriate amount of space and clearance between the two parts. Use trial and error for best results.
Furthermore, to print these parts successfully, you’ll also need to follow some important design tips if you are creating these models yourself.
This is the basic answer on how to 3D print connecting joints and parts, but there are more information and design tips that you’ll find helpful in this article. So, keep reading to find out more.
What Are Joints?
To best explain what joints are, let’s lift this definition from woodworking. Joints are a spot where two or more parts are joined together to form a larger, more complex object.
Although this definition is from woodworking, it still holds water for 3D printing. This is because we use joints in 3D printing to join two or more parts together to create a larger object with more complex functionality.
For example, you can use joints as the point of connections for assembling several parts in an assembly. You can use them to join parts too large to be printed on your 3D print bed as one object.
You can even use them as a means of allowing some motion between two otherwise rigid parts. So, you can see that joints are a great way to extend your creative horizons in 3D printing.
What Types of 3D Printed Joints Are There?
Thanks to 3D artists that keep on pushing boundaries of design, there are many types of joints you can 3D print.
We can loosely divide them into two categories; Interlocking joints and snap-fit joints. Let’s look at them.
Interlocking joints are popular not only in woodworking and 3D printing but also in stonework. These joints rely on the frictional force between two mating parts to hold the joint.
The design for an interlocking joint calls for a protrusion on one part. On the other part, there is a slot or groove where the protrusion fits into.
The frictional force between both parts holds the joint in place, usually reducing the movement between the two parts, so the connection is tight.
The box joint is one of the simplest interlocking joints. One part has a series of box-shaped finger-like projections on its end. On the other part, there are box-shaped recesses or holes for the projections to fit in. You can then join both ends together for a seamless joint.
Below is a great example of an interlocking box joint that you would find very hard to pull apart.
The Dovetail joint is a slight variation of the box joint. Instead of box-shaped projections, its profile has more of a wedge shape resembling a dove’s tail. The wedge-shaped projections offer a better, tighter fit due to the increased friction.
Here is a dovetail joint in action with the Impossible Dovetail Box from Thingiverse.
Tongue and Groove Joints
Tongue and groove joints are another variation of the box joint. We can use this joint for connections that need a sliding mechanism and other movements in one direction.
The profiles of their points of connection are just like those in box or dovetail joints. However, in this case, the profiles are more extended, giving the mating parts relative freedom to slide among each other.
You can find an excellent implementation of these joints in the very popular Modular Hex Drawers called The HIVE.
As you can see, the orange compartments slide inside the white containers, producing a tongue and groove joint that has a purpose for needing the directional movements.
It makes sense to 3D print sliding parts for certain designs, so it really depends on the project and operation as a whole.
Snap-fit joints are one of the best connection options around for plastics or 3D printed objects.
They are formed by snapping or bending the mating parts into a position where they are held in place by the interference between interlocking features.
So, you have to design these interlocking features to be flexible enough to withstand the stress of bending. But, on the other hand, they must also be rigid enough to hold the joint in place after connecting the parts.
Cantilever Snap Fits
The cantilever snap fit utilizes a hooked connector on the end of a slender beam of one of the parts. You squeeze or deflect it and insert it into the created gap to fasten it.
This other part has a recess that the hooked connector slides and snaps into to create the joint. Once the hooked connector slides into the cavity, it regains its original shape, ensuring a tight fit.
An example of this would be many snap fit designs you see in Thingiverse like the Modular Snap-Fit Airship. It has the parts designed in a way where you can snap the parts into place rather than needing to glue them.
The video below shows a great tutorial on creating easy snap fit cases in Fusion 360.
Annular Snap Fits
Annular snap joints are commonly used on parts with circular profiles. For example, one component can have a ridge protruding from its circumference, while its mating part has a groove cut into its rim.
When you press both parts together during assembly, one part deflects and widens until the ridge finds the groove. Once the ridge finds the groove, the part deflecting returns to its original size, and the joint is complete.
Examples of annular snap fit joints include ball and socket joints, pen caps, etc.
The video below is an example of how a ball joint works.
Torsional Snap Fits
These types of snap-fit joints utilize the flexibility of plastics. They work in a manner to a latch. A hooked connector with a free end holds the two parts together by latching onto a protrusion on the other part.
To release this joint, you can press the free end of the hooked connector. Other notable types of connections and joints that you can 3D print include hinges, screw joints, gutter joints, etc.
Maker’s Muse goes over how to design 3D printable hinges.
How Do You 3D Print Connecting Joints & Parts?
Generally speaking, you can 3D print joints and parts in two ways. These include:
- In-place printing (captive joints)
- Separate printing
Let’s take a better look at these methods.
In-place printing involves printing all the connected parts and joints together in their assembled state. Like the name “captive joints” says, these parts are joined together from the start, and most are often non-removable.
You can 3D print connecting joints and parts in place by using a small clearance between the components. The space between them makes the layers between the pieces in the joint weak.
So, after printing, you can easily twist and break the layers for a fully moveable joint. You can design and print hinges, ball joints, ball and sockets joints, screw joints, etc., using this method.
You can see this design in practice in the video below. I’ve made a few models that have this design and it works very well.
I’ll get more into how to design in-place joints in a later section.
You can also print them by using soluble support structures. After printing, you can then remove the support structures using the appropriate solution.
This method involves printing all the parts in the assembly individually and assembling them afterwards. The separate method is usually easier to implement than the print in-place method.
You can use this method for torsional, cantilever, and some annular snap-fit joints.
However, it lacks the design freedom the print in-place method offers. Using this method also increases printing time and assembly time.
In the next section, we’ll see how to properly design and implement both of these methods for printing joints.
Tips for 3D Printing Connecting Joints and Parts
Printing connecting joints and parts can be fairly complicated. So, I’ve put together some tips and tricks to help you make the process go smoothly.
A successful 3D print is dependent on both the design and the printer. So, I’ll be dividing the tips into two sections; one for design and one for the printer.
Let’s dive right into it.
Design Tips for Connecting Joints and Interlocking Parts
Select the Right Clearance
Clearance is the space between the mating parts. It is vital, especially if you are printing the parts in place.
Most experienced users recommend a clearance of 0.3mm for starters. However, you can experiment within the range of 0.2mm and 0.6mm to find what works best for you.
A good rule of thumb is to use double the layer thickness you are printing with as your clearance.
The clearance can be understandably small when printing interlocking joints like dovetails that do not permit relative movement. However, if you are printing a part like a ball and socket joint or a hinge requiring relative movement, you must use the proper tolerance.
Selecting a proper clearance accounts for the material’s tolerance and ensures all the parts fit together correctly after printing.
Use Fillets and Chamfers
Long slender connectors in cantilever and torsional snap-fit joints often come under a lot of stress during joining. Due to the pressure, sharp corners at their base or head can often serve as flash points or focal points for cracks and fractures.
Thus, it’s good design practice to eliminate these sharp corners using fillets and chamfers. In addition, these rounded edges provide better resistance against cracks and fractures.
Print Connectors with 100% Infill
As I mentioned previously, the connectors or clips in some joints experience high stress during the joining process. Printing them with 100% infill gives them better strength and resilience to withstand these forces. Some materials are also more flexible than others, such as Nylon or PETG.
Use a Suitable Width for the Connecting Clips
Increasing the size of these clips in the Z direction helps increase the stiffness and strength of the joint. Your connectors should be at least 5mm thick for the best results.
Don’t Forget to Check Your Clearances When Sealing
When scaling a model up or down, the clearance values also change. This can result in a fit that ends up being too tight or too loose.
So, after scaling a 3D model for printing, check and return the clearance to its proper values.
Tips for 3D Printing Connecting Joints and Interlocking Parts
Here are some tips on how to configure and calibrate your printer for the best printing experience.
Check the Tolerance of Your Printer
Different 3D printers have different levels of tolerances. So, naturally, this influences the size of the clearance you’ll choose in your design.
Furthermore, the printer’s calibration setting and the type of materials you use during printing also determine the parts’ final tolerance and fit.
So, to avoid poor fits, I recommend printing a tolerance test model (Thingiverse). With this model, you’ll be able to determine your printer’s tolerance and adjust your design accordingly.
You can get the Makers Muse Tolerance Test from Gumroad also, as shown in the video below.
I’d recommend checking out my article on How to Calibrate Your Extruder E-Steps & Flow Rate Perfectly to set you on the right track.
Print and Test the Joints First
Printing connecting joints is pretty hard and can be frustrating at times. So, to avoid wasting time and materials, print and test the joints first before printing the entire model.
In this situation, using a test print will enable you to test the tolerances and adjust them accordingly before printing the final model. It can be a good idea to scale things down for testing if your original file is quite large.
Use the Right Build Direction
The layer direction determines the strength of FDM-printed parts to a large extent.
For the best results, print the layers of the connectors parallel to the joint. So, instead of building the connectors vertically upwards, build them horizontally across the build plate.
To give you an idea of the strength differences that occur with orientation, you can check out the video that 3D prints bolts and threads in different directions.
That’s all I have for you on printing connecting joints and interlocking parts. I hope this article helps you print the perfect joint and expands your creative range.
Good luck and happy printing!