3D printing embedding

A Guide to Embedding Components in 3D Printed Parts

Markforged Mechanical Features [MMF] is a series of blog posts detailing best practices for designing common traditional engineering parts and mechanical features for composite reinforced 3D printing with Markforged printers.

Last week, we explored overprinting nuts as a method for strong connections within your industrial strength 3D printed parts. In this post, we’ll take it a step further: by using overprinting to design multi-material parts when different materials are needed in different components of a part. As a brief overview, the process for overprinting is fairly simple. You start a print, pause it midway, embed components into the 3D print job, and then resume the print, allowing it to 3D print over the components you have embedded.

‍Just take the build plate off, drop in the nuts, and continue the print.

This could be used to develop a more integrated product, with electronic components embedded in 3D printed parts, it could be used when two materials are needed in the same component for desired material properties, or, in the case I will be explaining below, can be used to prototype parts to be made with more expensive manufacturing processes before committing to large batch quantities. For this post, I’ve designed a pair of 3D printed pliers with customizable jaws and an ergonomic grip.

For this pair of pliers, I wanted a stiff body, but comfortable grips. The Onyx is a bit rough for grips but pretty stiff (especially with fiber reinforcement), so I used Onyx and fiberglass to 3D print the body of the pliers and jaws of the pliers and a comfortable, tough nylon 3D printed grip.

‍The CAD model of a pair of 3D printed pliers with custom jaws and an overprinted grip.

Designing for overprinting fundamentally branches from design for assembly: how can you make putting components together easy and fast? Because you are embedding components mid-print, and the printer needs a flat surface to print on and the print head must not intersect with the part being embedded, designing for overprinting thus comes down to designing a good cavity. So here’s a guide on modeling and 3D printing parts with embedded components.

Designing the Void:

When designing for overprinting, as I mentioned before, you will be embedding parts in a void. When you start your part design, you should think about which face the part will print from right from the beginning, as you’ll need to know this in order to properly embed a part. For this part, I want to embed the main body of one side of the pliers into the grips. All these parts happen to be 3D printed, but only the grips have to be for this case. If you are overprinting a part, you may need it to entirely fit within the printed piece, or like in the case of this set of pliers, you may just want to place a section of the part in, in which case you will need ribs or some other sort of feature to keep the part constrained, as shown below.

‍These 3D printed pliers have ribs on their handles for secure overprinting mounts.

To create the void, you’ll need a good CAD model of both the part you will 3D print and the part you will embed, then creating the void is as simple as creating a boolean operation: subtract the part you will embed from the 3D printed part. If the part you are embedding has filleted or chamfered top edges, those features will need to be removed from the part you are 3D printing – a flat ceiling is necessary.

‍Subtracting the model of the part you want to embed from the part that will be printed to create the cavity.

In CAD, you will also need to check for is features in the embedded part that will intersect the build plate or the extruder head. If a section of the part you are embedding extrudes up above the cavity, there is a chance the build plate will hit it. To account for this, you either should try to ensure that the part you are embedding has a flat top surface, or that the extrusion is far away enough that there is no chance the extruder head will hit it, taking into account all the movements of the extruder head, including zeroing and dislocation checking. On the Mark Two composite 3D printer, the plastic nozzle is about 35 mm from the front of the print head, so anything features in your embedded part closer than that may get hit by the print head In these cases, you must orient your part such that the embedded part is jutting out toward the front of the printer. If it juts out of the side or back, the print head has a higher chance of knocking into it because of the way the print head zeros and runs dislocation checks. For example, in the pliers I designed, the jaws are raised higher than the flat the grips will be printed around. The jaws were spaced to clear the extruder head, at just over 35 mm.

‍If there are any components with extrusions above the surface the overprinting will take place, make sure they have at least 35 mm clearance from the printed part.

A really important step to remember when designing your 3D printed part is accounting for tolerance. After you’ve performed the boolean operation, you’ll need to offset each face by about .08 mm on every face to ensure that you will achieve a surface flush with the layer this part will be paused on. This also applies to the walls of the cavity – if you can’t fit your part inside the cavity because the cavity is just slightly too small, then you won’t be able to fix it unless you print a new one! Better be safe than sorry and design the cavity a bit oversize.

‍Oversizing your cavity is important to ensure your part fits well – in Autodesk Fusion 360, I offset all the internal cavity faces by 0.

08 mm.

If your top surface is an odd geometry, you’ll need to design a secondary insert to add to the cavity to ensure a secure fit that forms to the top surface of the embedded part. This process is explained in the latter half of my embedded nuts blog post from last week, and the exact same process can be implemented for other components. If you would rather not do this, one way to get around this involves angling the ceiling of the cavity above the inserted part, but then that means the component, depending on it’s geometry, may be loose within the 3D printed part.

‍This cross section shows a square nut embedded at an angle, with a triangular piece to fill the gap.

Usually, when designing for overprinting, I try to avoid the use of support material. However, in some cases it it necessary to the design, and that’s not a problem: support material can be easily removed from the cavity before placing in the embedded component.

Adding pauses in Eiger:

In Eiger’s internal view menu, you can easily add a pause after a selected layer, making it easy to embed parts into your 3D printed components. Find the layer just before the roof of the cavity starts to print, and click “Pause After Layer” At that layer, you can note the time it will take to get to the pause and use that to determine when to check in on your print job.

‍Select “Pause After Layer” to add a pause after the printer finishes the selected layer.

Remember, if your parts do not require support material, it is a good idea to turn supports off. If they do, however, that’s fine! You’ll be able to remove them, as I’ll explain later.

An Eiger screenshot of the 3D printed grips I’ll be printing.

When you orient your part on the build plate, keep in mind the accessibility of the part. You’ll want to be able to quickly pop the part in and resume the print, so orienting your part so that you can easily get to it. For this part, I placed it all the way up by the front so I could easily snap in the body of the pliers.

‍Set up your part in Eiger so it is easily accessible once the print pauses.

Adding the Part:

When it comes time to add the part to the print, timing and speed are key. As Markforged printers are FFF (Fused Filament Fabrication) machines, the plastic is heated, extruded, and cooled. When it cools, it shrinks slightly, which, if the print is paused for long enough, can cause much weaker layer adhesion on that plane. When placing a part into a print job, you want to do it as quickly as possible to reduce this risk. Using Eiger, you can estimate about when your printer will pause, so you can show up on time and be prepared for when your printer pauses.As I explained earlier, support material may be necessary due to other features in your design. For example, this grip requires supports because it has a complex bottom surface. In my case the void that I designed will fill with supports, but it’s not a problem – if this happens you can just pull them out before inserting the part.

‍You can easily pull supports out of a cavity before inserting an embedded part.

Now it’s time to place the part into the print. This is why tolerances are so important. You need to make sure that the embedded component is perfectly flush or slightly below the layer that the print is paused at. If it is slightly raised, your print head will jam against the embedded component and mess up the entire print, or the filament will jam when trying to print over the component.

‍embedding the 3D printed handle in the ergonomic grip.

When a print pauses on the Markforged 3D printer, the print head moves out of the way, allowing you to easily remove the build plate from the printer and add your part. The kinematically coupled build plate ensures the print bed will snap right back in place when you want to continue.

‍The build plate snaps into place with 10 micron accuracy.‍The 3D printed grip continuing to print over the handles of the pliers.

If you are adding a component that is not a Markforged 3D printed part, then you will need to add a layer of glue to the top surface of the part. This glue is normally put on the build plate at the beginning of a print to help with build plate adhesion, and in this context we are using it for the exact same reasons – the nylon will stick better to the top surface of the part.

‍The completed print job for these 3D printed custom pliers.

And after printing two of these and snapping in a small pin at the joint, I now have a pair of 3D printed pliers with customizable, swappable jaws and ergonomic grips!

‍The finished set of 3D printed pliers.‍After printing, the pliers can be easily assembled, and you can make modular grips for the jaws!

If you want to make these yourself, here are the files:

Pliers and pin MFP (requires Onyx and fiberglass)

Grips MFP (requires Nylon)

Custom JAW MFP (requires Nylon)

Pliers STL

Pin STL

Grip STL

Custom Jaw STL

Other Applications:

The applications of overprinting range far and wide because it allows you to create fully integrated assemblies that could not have been created any other way. While this example represents embedding a section of a component to create an ergonomic grip, you can also embed whole components and the same rules apply. For example, you may want to prototype a part that will eventually be overmolded, or you may want to create a part with embedded electronics for an integrated electromechanical system. You may want to embed hidden nuts or bearings into a 3D printed part, or create a multimaterial build with a single plastic extruder 3D printer. If you have tried out overprinting and embedding components in 3D printed parts, please share with us on Twitter, Instagram, or Facebook!

Embedding Nuts in 3D Printed Parts for Hidden Fastener Strength

We’ve covered how to get around this previously by adding some metal to your 3D printed plastics with heat-set threaded inserts. The insert melts and reflows the plastic around the part, making it stronger and more secure. However, this may not always be a good option – while inserts do work, they have a few design constraints. The insert must be on the face of a part and its pullout strength cannot be further reinforced beyond the material properties of the plastic surrounding the insert.

‍Putting a heat-set insert into a 3D printed part.

There are workarounds for this, however, in the form of overprinting. This technique goes by a few names: overprinting, co-processing, and embedded printing are just a few. The technique is similar to over-molding in injection molding and casting procedures, in which parts are placed into the mold and the plastic or rubber is cast around them. One example would be how scooter wheels are made — the rubber tires are actually cast around the metal hubs.

‍A pair of Razor scooter wheels. The polyurethane tire is cast around the plastic hub of the wheel. (source: Razor)

Overview

We can take advantage of this technique in 3D printing as well – by embedding external components into a print during a pause. This process allows you to make some neat impossible-to-manufacture assemblies. By embedding nuts into 3D printed parts, we can add more material between the bolt and the nut than would be possible with an insert to both hide the nut and increase the pullout strength. We can even reinforce the layers sandwiching the nut further with fiber, allowing for strong, hidden bolt connections within your industrial-strength 3D printed parts. The basic design process for this is designing a cavity the size of the embedded nut you want to add into the 3D printed part, pausing the print just before the top layer of the cavity is printed, adding in your component, and allowing the print to continue.

Design Guidelines:

Tolerances: When embedding components into 3D printed parts, the biggest thing to remember is the tolerances of your printer. On the Mark Two, leaving a .05-.08 mm gap on all sides gets you a pretty nice close fit for your part. This should be of the measured dimensions of your part, just to be safe. The reported dimensions from a manufacturer will always have their own tolerances! A cavity that is too open won’t engage with the outside of the nut, so you won’t be able to thread a bolt into it. A cavity that is too small, well, you won’t be able to fit the nut into it.
The Top Surface: The top surface of the part you are embedding is pretty important as well. If the top of the part you’re embedding has a flat face, you’ll probably want to design your part such that the printer will print right on top of it, in which case you may want to lay down some glue on the top of your part. If the top of the part isn’t flat, you’ll need to design a cavity that doesn’t touch the top of your part when printing. Either way, the top surface of the part you are embedding MUST be below the print head as soon as it is placed into the 3D printed part, or else the print head will be sad and may run into it. One of the most important things to remember when designing your part is what face it will be printed from and where the pause will be.
Support Material: Ideally, you don’t want to use supports when embedding parts because they will get in the way. However, if you have to due to other features in the part, you’ll need to remove them during the pause before you put the nut in, and ensure that no supports will be printing over thin air or on top of the nut once it has been embedded.
Selecting Nut Type: When it comes to embedding nuts in your designs, square nuts are actually much more suited for this application because they are less likely to strip the inside faces of the cavity if you torque them too hard. However, hex nuts are much more common and well known, so in this guide I’ll primarily be using hex nuts because likely that is what you are familiar with. If you really want to get into this, square nuts would be a good investment.

Embedding Nuts in the XY Plane

1. Designing the Cavity: Designing the cavity for your nut is fairly simple. Once you have your bolt hole designed, measure the dimensions of the nut you are embedding, and CAD in the cavity using the bolt hole as a centerpoint. Usually, I will make a construction plane at either layer that the cavity will begin or end and create a sketch on it.

‍The plane I’ll make a sketch on for the nut cavity.

Next, measure the nut you’ll be embedding and sketch out the cavity. In this case, I’m using an M5 hexagonal nut with a width of 7.85 mm and a height of 3.85 mm. I measured this directly with a set of calipers instead of using the spec sheet, which says it is 8 mm x 4 mm. Instead of entering in the nut dimensions directly, account for tolerances – about .05 mm on each side (so add 2 x 0.05 to get 0.1 for the full diametral tolerance) gives a pretty close fit. That’d give me 7.95 mm width and 3.95 mm height, but I want to play this one safe, so I’m going to give myself a bit more wiggle room and round up to 8 mm width and 4 mm height anyways.

‍Sketch the nut profile, with tolerances included, on the plane.

After that, extrude the sketch up by the calculated height dimension and now the cavity is done. You don’t want to fillet or chamfer any of the edges internal to the cavity because that will affect the fit of the part and where the print nozzle goes – for example, if you fillet the ceiling edge of the cavity, once the pause comes, you won’t be able to fit the nut into the cavity!

‍Extrude the sketch to make the cavity.

‍A cross section of the nut cavities for the bracket.

2. Adding a Pause: In Eiger, you can add a pause after a given layer. First, ensure that you have turned off supports (unless you really need it). You can do this under “Advanced Settings”.

‍Turn off supports under advanced settings.

Next, find where in the sliced file the ceiling of the cavity begins, and scroll to the layer BEFORE that. There, you can click “pause after layer” to add the pause.

‍Add a pause with the “Pause After Layer” feature.

3. Adding Fiber: To increase the pullout strength of your nut, you may choose to add fiber to your part. You’ll want to add it on the layers above or below your part. This really depends on the direction your bolt will be coming from and how it will be loading the nut. For more info on laying out fiber effectively, check out this series of posts. In the image below, I’ve added fiber to either side of the nut cavities to strengthen the bracket. Fiber can also be added to the layers that make up the sides of the nut to reinforce the walls of the cavity. Stronger walls means a more secure nut that will be less likely to twist itself loose.

‍Add fiber above and below the nut for increased pullout strength.

4. Printing the Part: Now it’s time to hit print. fortunately, you can figure out when the printer will pause by looking at the layer details in Eiger, so there’s no need to wait around. Once the pause occurs, just slip your component in and resume the print. If you are concerned about the nylon or Onyx no sticking to the top of the embedded component, just add some of the build plate glue we provide to the top face before you resume the print (however, be careful not to get glue on the print itself – this can cause layer delamination). If you have some nuts that are hard to reach from the front of the printer, no worries! fortunately, the kinematic couplings on the bottom of the build plate snaps back in with 10 micron accuracy, so you can just take the build plate off and pop it back in place once you’ve embedded all of your components.

‍Just take the build plate off, drop in the nuts, and continue the print.‍The 3D printed part with embedded nuts in view.

5. Dealing with Support Material and more complicated geometries (if necessary): If you need to use support material because of other features in your part, then when the print is paused you can pull it out with a pair of needle-nose pliers. However, this only really works if your cavity has a flat ceiling. If you are embedding parts with more complex top surfaces, you may not be able to use support material. You’ll either need to rely on arched or angled overhangs to keep the internal cavity clear, or print a secondary piece to embed with a flat top surface to make removing support material easy. This process is explained below.

Printing Secondary Parts to Embed Nuts on Other Planes

Adding embedded nuts on other planes is possible, but a bit more design consideration is involved so that support removal is easy and so that the nuts remain constrained within the part. To do this, a secondary component must be designed. As an example, I would like to embed a hex nut into this piece such that its axis is parallel to the build plate, as shown in the cross section below. A square nut would be the simple solution to this, because it provides a flat surface to print on, but I am going through for the sake of example. If I leave this cavity as is, the filament will not be able to bridge the gap very well, and any support material in that area will need to be removed.

‍With a pure flat overhang, the sides of the ceiling are unsupported.

I could incorporate an angled overhang into the cavity, but that still means I can’t use support material as it will fill in poorly above the nut, and it means the nut will be able to slide within the cavity, making it much harder to secure when threading a bolt through it.

‍With an angled overhang, the nut will spin inside the cavity and will be hard to fix.

Instead, I can add a secondary part to print, a feature that will secure the nut and provide the printer with a flat top surface to print on. To do this, I make a nut cavity with a flat top:

‍With a bit more space in the cavity, we can integrate a secondary part to secure the nut.

And then create a small piece that fills in the remaining space in that cavity, leaving a bit of tolerance on the top and sides just to be safe.

‍With a secondary component, the nut can now be secured within the cavity.

This can be printed alongside the main component, so that when the print pauses, I can add in the nut and the secondary component in during the pause, and then the print can continue over the flat top of the secondary printed part, like with this angled square nut below:

Using the same method you can embed nuts at other angles, too, but you need to make sure you have room to slide the nut in. In the cross sectional image below, the small, triangular piece secures a square nut in place at an angle within the printed part:

‍This cross section shows a square nut embedded at an angle, with a triangular piece to fill the gap.

‍By adding secondary inserts, you can make bolts come out at all sorts of angles.

This technique can allow you to secure nuts at any angle on any plane in 3D printed parts, and it isn’t limited to just nuts either – figure out how embedding nuts and other components is most useful to you, and don’t forget to share it with us on Twitter, Facebook, or Instagram!