# 3D printing
## Lesson for Open Hardware Academy

Date: 29-08-2022

## Introduction
In this lesson you'll be introduced to 3D printing; how it works, when to use is, how to get started with 3D printing, and some tips and tricks. It contains exercises to teach you how to make a digital 3D model and how to prepare that model for printing.

This requires you to some specific software. We’ll use “slicer” software Cura, [download that here](https://ultimaker.com/nl/software/ultimaker-cura) (free). And we’ll ask you to make models in CAD software. If you are already familiar with CAD software and you prefer to use that, please do! If not, we recommend TinkerCAD as an easy start. It’s web-based but you do need to make a (free) account, [which you can do here](https://www.tinkercad.com/join).

This lesson is an amended version of a presentation originally held in February 2022. It will go over 3D printing by answering a few main questions: What is 3D printing? When should you use 3D printing? And how do you 3D print an object?

:::info
**By the end of this lesson you will**
- know what 3D printing is
- know when 3D printing can be used as a production technique, and when it's a bad idea
- be able to make a simple 3D model
- be able to prepare your print in slicer software to create the right print for your application

**Learning objectives**
- Basic understanding of what 3D printing is and when you can use it.
- Be able to use 3D printing as a prototyping or production technique for your project
:::

This is the goal: You know how to model simple products such as a keyhanger and know how to print it.

## 3D printing: what?
### Different 3D printing techologies
There are multiple forms of 3D printing. 3D printing, or additive manufacturing, is an umbrella term for production techniques in which a model is gradually build. Consequetive layers of material are gradually added on to each other to physically create a model that was designed digitally. Each of the bullet points below links to external in-depth information.

 • [Stereolithography](https://formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing/) (SLA): Selective hardening of a liquid resin by light
 • [Selective Laser Sintering](https://www.hubs.com/knowledge-base/what-is-sls-3d-printing/#how-does-sls-3d-printing-work) (SLS): Fusing powders together in a shape with a laser
 • [Multi Jet Fusion](https://all3dp.com/1/multi-jet-fusion-mjf-3d-printing-simply-explained/) (MJF): Fursing layers of powder with two selective liquids
 • [Material Jetting](https://all3dp.com/1/what-is-material-jetting-3d-printing-basics/): Tiny droplets of various materials are sprayed and solidified with UV light.
 • [Direct Metal Laser Sintering](https://www.3dsystems.com/how-does-metal-3d-printing-work) (DMLS): SLS but with metal powders
 • [Electron Beam Melting](https://www.3dnatives.com/en/electron-beam-melting100420174/) (EBM): SLS but with an electrobeam instead of a laser
 • [Fused Deposition Modeling ](https://all3dp.com/2/fused-deposition-modeling-fdm-3d-printing-simply-explained/)(FDM): extruding thin lines of molten plastic

.. and more. But in this lesson we'll focus on FDM printing because it is the most widespread and cheap technology. For small scale Open Source production and prototyping, this is the most obvious choice.

### How FDM printing works
FDM printing is the printing you'll think of when someone says "3d printing", the techology you'll see most at universities and maker labs. A thermoplastic string on a spool, the 'filament', is slowly fed to a heated moving head, the 'extruder'. In the extruder the plastic melts and is pushed through a small hole, the 'nozzle'. The molten plastic is deposited on a 'print bed' or on previously deposited layers. The plastic solidifies and slowly a shape grows.
*Credits for the image to [ISD-soft](https://isd-soft.com/tech_blog/oh-3d-printer-office-fdm-printing-basics/).*

Generally the extruder moves slowly upwards and moves horizontally in the x direction while printing one layer. The print bed moves horizontally in the y-direction. The printer is told how these parts should move by a code called the 'Gcode'. This code is created in software called 'slicer' software, in which all kinds of settings can be adjusted. The 'slicer' first needs a 3D model of the part that you want to print, before you can adjust the settings. This 3D model is commonly imported in .STL format, it can be produced in a lot of different programs called CAD software. In this lesson you'll learn how to make a model in CAD and prepare a print in a slicer.

*Credits for the gif to [3D Currax Solutions](https://www.3dcurrax.com/technology)*

## 3D printing: when?
### Benefits & drawbacks
3D printing has a number of benefits over other production techniques:

* It has low start-up costs. You don't need many tools, an expensive mould, or highly skilled laborers. Only a printer and filament.
* You can easily create complex shapes, Much easier than through milling or moulding for instance
* You can make quick iterations because you don't need a mould and produce directly from a digital 3D model
* Printed objects can be detailed with high accuracy, depending on your printer and your printer settings

But it has drawbacks as well:
- Production time per item is long
- this makes production too slow for large batches
- and makes production of large volumes expensive

### When to use 3D printing
This combination of benefits and drawbacks makes 3D printing suitable for a number of aplications:
- A fun technical hobby. It doesn't always have to be serious or professional.
- Small production series
- Personalisation. Items that are customized to a specific user. This can be regarded as an extreme small production series.
- Prototyping or testing of parts of the product during the design
- Decentral production, which are again small production series spread over different locations.

The last four points are all related to Open Source Hardware design.

#### When not to use 3D printing
Not only is 3D printing too expensive and slow for small production volumes, the energy and material consumption is too high to be wasted on '[stuff](https://www.thingiverse.com/groups/pokemon/things)', [figurines](https://www.thingiverse.com/groups/star-wars/things), and [unnecessary](https://www.thingiverse.com/groups/tanks/things) [models](https://www.thingiverse.com/search?type=things&q=&sort=popular&posted_after=now-30d&category_id=107&page=1) (author's opinion).

## 3D printing: how?
### Step by step
When 3D printing, you'll always go through 8 basic steps:
1. **Idea**. Come up with what you want to print. Let's say a keyhanger.
1. **Sketch on paper with basic sizes**. You make a sketch of how it should look. Specify the sizes.
3. **Find the basic shapes**. Look for the basic shapes to build you design from such as a rectangle, tube, and ball. Most non-organic shapes can in essence be brought down to a combination of basic shapes.

5. **Design in CAD.** Build your digital 3D model by combining the previously foud basic shapes. Most CAD software is based on this principle.

7. **Set printer settings in slicer software.** With slicer software you decide how the printer converts the digital model to a physical part. You can adjust how fast, detailed, strong, and beautiful the result will be in the slicer software.

9. **Check layers.** Allways check you layers! In a virtual simulation of the layers printed by the 3D printer, you can see check if no weird things might happen during printing.

11. **Print.** Send the G-code to the printer, let the printer do it's thing.
13. **Post-processing.** No always needed, but sometimes you need to sand your model a bit, cut away supports, or smoothen surfaces or drill holes.

Do not all of the above words make sense? No worries, we will get there.

### Slicing a model

We'll leave the chronological order now. To better understand how to design good 3D printable parts later, we'll first cover the slicer software and printer settings.

A slicer is software in which you can import a 3D model and 'slice' it in to layers that can be printed by the 3D printer. In the slicer you decide how the virtual 3D model is translated to a plastic printed model. For instance, how thick the layers are, how many layers are printed on the outside of the model, and kind of structure the inside is filled with.

There are many different kinds of slicers. We'll use Cura for these execises. It's free, it's open, it works well.

[Download it here.](https://ultimaker.com/nl/software/ultimaker-cura)

This is how it looks:


**A first video explanation of the basics is needed**

There are good Cura tutorials on YouTube.
Here's a good [complete one](https://youtu.be/l_wDwySm2YQ?t=345) (best to start at 5:45).
{%youtube l_wDwySm2YQ %}

But if you're impatient here's a [good short version](https://youtu.be/eUNTlb5pEWA?t=328) (start from 5:28)

### Slicing exercise
:::warning
**Exercise 1 (beginner)**: Download [this cable holder](https://www.thingiverse.com/thing:2798023/files) and create a Gcode for as many copies at once as you can, within these constraints:
- Printing time is under 1 hour
- At least 2 solid layers on all sides
- Use a infill that looks stiff enough


**Exercise 2 (advanced)**: Download [this astronaut](https://www.thingiverse.com/thing:230305/files) and create a Gcode for a good looking print. Think what additional parameters and settings you need to change in CURA to be able to get a correct and nice looking print.

:::

### Creating a 3D model in CAD
#### CAD software
CAD is an abbreviation for Computer-Aided Design. This is software used to create and analyse all kinds of designs. It's safe to say all of today's products and machines are first modelled in CAD software. Consequently, a lot of different types of CAD software exist. We've listed a few:

**[TinkerCAD](https://www.tinkercad.com/) & [BlocksCAD](https://www.blockscad3d.com/)**: Free web-based modelling application in which you can create simple parts by combining and adjusting shapes with your mouse. Ideal for starters and kids.

**[Google SketchUp](https://www.sketchup.com/) / [FreeCAD](https://www.freecadweb.org/) / [Fusion360](https://www.autodesk.eu/products/fusion-360/overview?term=1-YEAR&tab=subscription)**: More advanced modelling software. SketchUp and Fusion360 are again web-based. All three are free to use, Fusion360 only for non-commercial use. They have more extensive options to create parts and assemblies of parts, detail and adjust dimensions.

**[Onshape](https://www.onshape.com/en/)/ SolidWorks / CATIA / Rhino /AutoCAD / etc**: The professional stuff. AutoCAD and Solidworks are the market leaders in CAD software for professional engineers. Rhino is especially used to create more organic shapes by product designers and artists. Onshape is a webbased application that is limitedly useable for free for non-commercial applications, and the preferred software of the author.

**[OpenSCAD](https://openscad.org/)**: An odd one in this list since it is script-based modeling software. You have to code your shape, this creates parametric designs that can be easily adjusted by changing parameters in the design. Preferred by the older and more accurate designers in the Delft Open Hardware community :).

#### Getting started with CAD
If you are already familiar with CAD, why are you reading this? Don't make life hard, use the software you know. If you've not used CAD before, we recommend to use [TinkerCAD](https://www.tinkercad.com/). You don't need to download anything, it's free, it's just not open and you need to register (but that's not a hassle).

It looks like this:

The best way to learn designing products in TinkerCAD is to just start messing around. However, you need to know something about the controls and where to find which button. This 9 minute [tutorial](https://youtu.be/gOs6Mdj7y_4?t=71) will explain all you need to know (start at 1:11).

{%youtube gOs6Mdj7y_4 %}

### Modelling exercise
:::warning
**Exercise 1 (beginner)**: create a name tag for yourself or a loved one. It doesn't have to be one as [the example](https://hackmd.io/pVnRQfivSkOsd6ixdPiq6A?view#Step-by-step) used before. Go nuts if you want to.

**Exercise 2 (advanced)**: create a spool or other item to wind up head phone cables. Your product should prevent the cable from unwinding in your pocket and keep the earbuds safe.

*If you are a regular CAD user, don't worry about the exercises. Put the time in developing your project.*
:::

### Design guidelines for 3D printing
This chapter should actually be called *"Design considerations to make the best models and be able to print them (using FDM) and fit your application best"*. But that's a long and boring title. The truth is that there are no universal design guidelines for 3D printing.

It is important to keep in mind that a printed part is build in stacked layers of molten plastic and each layer needs to be printed on a previous layers a cannot be printed mid-air. Further than that, the considerations that you have in your design are based on multiple factors,

* Most considerations have to do with the structural integrity or looks of the print
* ... but it depends on you how much you care about these
* A lot of things are possible if you don't mind how long your print takes
* ... or how much material is used
* ... or if you have to do some manual post-processing to your piece
* Some printers can print more accurate parts than others, just changing the width of the nozzle can already make a huge difference
* And some 'mistakes' in the design can be fixed with the right slicer settings if you are willing to spend time on that.
* Different materials require different settings such as print speed, temperature, and minimal nozzle size

**However**, some guidelines can be given if we assume that you are trying to make an average prototype print for your project, that you have a decent mid-price range printer using a 0.4 mm nozzle. You are patient but economic with material and want to do as little extra work as possible. Does that sound like you? Yeah, thought so.

**1. Overhang: do not print mid-air**
You can't print in the air, the molten filament needs something to be printed on. But you can print the next layers halfway over the previous layer. Like in the simplified cross-section below.
* This means that you can print slopes of about 45°

And if your extruder is moving fast enough between to supported parts, you can 'bridge' some plastic in the air between the two supported ends.
* You can bridge gaps of about 20mm

These sloped overhangs and small bridges can be seen in the example below.The top part was printed upside-down. That's why the overhang was needed. Click on the image to enlarge.
[](https://i.imgur.com/HZKGuf1.png)

* But you can also use ‘support’: scaffolding under your overhang, that is printed in previous layers. But this requires more material, costs more time, and requires post-processing to remove the supports.
* Or you can lower your print speed + use a higher fan speed + lower print temperature + and pick right infill. But this requires trial and error.

Below is are an example of a lot of 'support' used to support overhang, and what happens if you use too long bridges. Again, click to enlarge.
[](https://i.imgur.com/J2QhN0Q.jpg) [](https://i.imgur.com/7PuH2Jy.png)

**2. Strength is in horizontal print direction**
You print is at the weakest between to printed layers at the cross-section of your print. Take into account in what direction your model is going to be loaded. Choose the printing orientation accordingly or strengthen your part.
[](https://i.imgur.com/zko3dIG.png)
[](https://i.imgur.com/8PAXEX7)

**3. Minimal wall width**
What is the thinnest single wall that you can print, that will stay straight? That depends on how high you want to print.

* For small shapes (few layers high), the wall can be as thin as you set ‘Line Width’ in your slicer. But you should keep ‘Line Width’ within 75%-125% range of nozzle size.

In the example below the designed wall is so thin that it can't be printed.
[](https://i.imgur.com/e0CPF5p.png) [](https://i.imgur.com/JfoFLBJ.png)

* For large shapes (many stacked layers), the minimal wall width is 2x the line width. So, 0.5-0.8 mm.

In the example of a card holder below, a thin straight wall was needed, it is 2 lines thick.
[](https://i.imgur.com/r5z2bFb.png) [](https://i.imgur.com/ZfwTB3v.png)

* You can use thinner walls, if your 3D printer has very accurate stepper motors + a fine driving belt, you use a small nozzle, and you use slow print speed.

**4. Tolerance for fitting pieces**
If you want two or more pieces to fit well into each other, if one should slide of grip into the hole of another piece, what is the tolerance on your pieces? This should be about 0,1 mm on each side. In the example below this means that the pin should be 0,2 mm thinner than intended, and the hole in the ring 0,2 bigger than intended.

### Model & Slice exercises
:::warning
**Exercise 1 (beginner)**: Create and 'phone stand' in which your can place your phone to hold in an angle so you can watch a video on it. Prepare the print in Cura and try to use as little material as possible and minimize printing time.

**Exercise 2 (advanced)**: Create a bracelet with an intricate design. Use arches, stars, diamonds, whatever, be creative. Than prepare it for printing in the slicer. One critical requirement: your bracelet has to be able to be printed in 30 minutes.
:::

## Further reading
https://www.hubs.com/knowledge-base/key-design-considerations-3d-printing/
https://www.hubs.com/knowledge-base/enclosure-design-3d-printing-step-step-guide/
https://all3dp.com/1/types-of-3d-printers-3d-printing-technology/

## Thanks to
This lesson is made possible by:
Jannes Nelissen and Andjela Tomic

## Contact
Link to [Academy website](https://www.openhardware.academy/)