07 : Computer Controlled Machine

1. Summary

Hero Shot

Tensegrity Shelf

Learning Outcomes

What did I learn this week ?

• CAD :
  • Fusion 360 extrusion from .svg
  • Manual dogbones joints in Fusion
• Fusion to G-code :
  • Fusion workflow to generate G-code
• CAM :
  • How to use Linux CNC
• Machining
  • Tools properties
  • How to safely use a CNC machine

Lecture Content

Christophe, one of our local instructor is in charge of teaching how to use the CNC machine. He prepared a special (intense) course for us. He thaught us how to use Fusion 360 for machining, explained the safety rules of our local machine and showed us how to start it.

Fusion 360 for machining

A CNC machine requires instructions as G-code file. As for 3D printing, we could directly write the G-code but it can rapidly become too complex. Therefore one must use a software (often with a GUI) that generates Gcode from more user-friendly written instructions.

We will use Autodesk Fusion. Christophe prepared a 3D file containing quite complex shapes and we had to follow and reproduce step by step what he did to generate the G-code.

Before anything else we had to open the given fusion file (.f3d) in the software :

Posage

The first step is to define a new Posage which are instructions for the machine to understand the size and position of our brut material and where it will have to cut. In the french version of Fusion, select FRAISAGE > POSAGE > Nouveau Posage :

Built-in "documentation"

If you are not sure what a thing is in Fusion 360, you can let your cursor a few seconds on the thing and a window explaining what it is will open. You can see an example on the picture above. It can be really helpfull !

After selecting Nouveau posage, a box will open on the right containing three tabs. The most important are the two first ones.

The first tab Posage allows one to define the coordinate system of your object. The second one Brut defines the shape and position of your brut material.

Once the posage is defined, one must use different built-in functions to cut the different parts of the piece. However one must first tell Fusion what tool will be used to cut.

Defining the tool

To define the tools you will use to cut, go to GÉRER > Bibliothèque d'outils :

A window will open containing all your defined tools. To add one, select the + and then your tool type.

A new window opens and allows to define the tool properties as the cutting length, the cutting diameter or the body diameter. One must also define the desired tool motion by defining the cutting speed, the free speed, the rotation speed, etc. These latter properties also depends on the material you are using. One must check its tool datasheet to define all of the required properties.

Be carefull !

One must carefully do these steps. A bad tool definition could lead to a broken tool.

2D Cutting Functions

Now that the posage and the tools are defined, one may start defining the cutting instructions by using the built-in functions.

Each time you select an operation, a box opens on the right side of the window in which you can edit the operation's settings.

The box contains different tabs :

• Tool
• Multi-axis
• Geometry
• Heights
• Passes
• Linking

The Tool tab contains your selected tool properties. One should not modify anything if its tool was correctly defined previously.

The Multi-axis tab concerns multi-axis machining which we will not cover this week.

The Geometry tab is where one select the cutting location.

The Heights tab ...

The Passes tab controls the number of passes to cut the desired part.

The Linking tab ...

Face Operation

If the brut material is thicker than the desired piece, one should use the face operation to remove the extra material on the whole brut material surface.

Poche Operation

Adaptative Operation

Alliesage

Contour

2. Assignment

This seventh week's assignments are :

• Group :
  • Do your lab's safety training
  • Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
• Individual :
  • Make (design+mill+assemble) something big (~meter-scale)
• Extra :
  • Don't use fasteners or glue
  • Include curved surfaces
  • Use three-axis toolpaths

Below you will find the achievement of the latter.

2.1. Safety Training

The CNC machine of our Fab Lab is a High-Z S-1000/T by CNC-STEP (software : LinuxCNC) and is covered by a large case for safety reasons :

The first thing to ask is where is the emergency button, it is just on the right side :

The basic safety and usage rules are written on the doors :

• Wear protection glasses
• Make sure you leave the space clean for the next user

Patrick then showed us how to remove and install a tool. You first have to unscrew the aspiration :

Once unscrewed, you should be able to put it away :

You can then unscrew the tool base :

Once removed, you get two pieces : the collar and the tool.

Keep the colar and install the new tool in it.

You can then follow the previous step in the opposite order.

To complete the training, Christophe asked us to design a simple and small piece in order to cut it quickly to teach us the safety rules before starting the group and individual assignments.

Using the Fusion 360 built-in functions, I designed a "FOG" sign for the fog generator.

I screwed my brut wood plank to the CNC work plane and launched the milling. Everything was working correctly but I was a bit wooried about the sawdust quantity. Christophe told me it was not a problem but showed me anyway how to pause the machine to clean it.

We have a portable vaccum cleaner for that.

All you need to do is to pause the milling in the software,

then turn of the engine,

then clean,

and finally you return on the engine and press the pause button again of the software.

The result was quite satsifying.

I unscrewed the brut plank and I had to break the fasteners with the tools below,

Once my sign was detached of the brut, I had to sand it in order to make it smooth.

I used a sandpaper

and the result was indeed smooth :)

2.2. Group Assignment

For the group assignment, each one of us was in charge of a different task. Check Michel and Fabio websites for the other tests !

I was in charge of the kerf test therefore I simply milled two 5 cm squares. One with a Poche function and another one with a Contour function.

The first one has a negative 0.5 mm error.

The second one has a negative 0.4 mm error (indeed with a 6mm tool, we should measure 62 mm).

Fabio was in charge of the brush test but since I was with him when he did, I also took pictures. The brush was a bit rough so we smoothed it with sandpaper.

The measurement shows a negative 0.2 mm error on the middle hole.

However by forcing a bit, the middle holes formed a good joint.

Nevertheless it was hard to separate them after joining them, the largest joint is better.

2.3. Individual Assignment

At first, the goal of my individual assignment was to do a tensegrity stool.

I got inspired by this video from Aribabox YouTube channel who did a CNC cut tensegrity stool. It seemed a bit ambitious to make something functional but I really wanted to try it !

Aribabox Video

I designed my own version using Inkscape and while designing it I decided to make a high shelf instead. It would be nice if I could put a plant on it ! I did a round "70's" design.

I imported the .svg file in order to extrude it but the .svg importation is a bit weird in Fusion. It scales it down a bit... Therefore I measured the imported size of the square and scaled up everything by the required factor to get a 40 cm square.

I extruded the design to make it 3D and defined the cuts as explained in the lesson part.

I forgot to take more pictures of the process... but here are the resulting pieces !

I then had to assemble everything with strings... It seemed complicated but hopefully, in the Aribabox video, he shows a special knot that is quite easy to do and that allows one to adapt the tension in the string !

Aribabox Video

It is called a Prusik knot and he found it on Netknots. Below are the Netknots instructions to do it but I had a hard time trying to understand them hence I just copied what he did in the video.

Prusik Knot

Here is the almost final result, it lacked stability so I modified a but the strings tensions.

It is better but still a bit unstable...

I can put light stuff on it but defenitely not a plant !

Here is a vidoe showing this weird force balance. It really seems to float !