7. Computer Controlled Machining (CNC)¶
Overview¶
This week was all about Computer Controlled Machining (CNC) — getting to understand how a digital design turns into a real, physical object cut by a machine that follows nothing but code.
During this week I learned:
- what a CNC milling machine actually is and how it works
- the complete CNC workflow, from CAD file to finished part
- the role of Aspire 9.5 in generating toolpaths
- the role of UGS CNC (open-source software) in talking to the machine
- the importance of machine axes, cutting tools, feeds and speeds
- and most importantly, the safety rules around CNC machines
Safety was something I paid extra attention to, mostly because my final project is also a safety system, so thinking carefully about risk and protection felt very close to home this week.
Group assignment¶
Our group assignment was carried out together with my classmate Ani Petrosyan, and at Fab Lab Gyumri together with instructors Rudolf Igityan and Mkhitar Evoyan. As a group we went through the CNC fundamentals, safety procedures, and machine workflow together, then tested it on the OLSK CNC at Fab Lab Gyumri.
For more details, you can check out the full group assignment page.
Machine Overview¶
For this assignment we used the OLSK Large CNC V1, the large format CNC mill available at Fab Lab Gyumri. It’s an open source design by Daniele Ingrassia of InMachines Ingrassia GmbH, part of the Open Lab Starter Kit (OLSK) family of open source digital fabrication machines.
Specs of the machine:
- Milling volume: 2500 × 1250 × 300 mm
- Frame: steel pipes combined with CNC milled solid aluminum and profiles
- Motion: 25 mm ball screws, rack and pinion
- Guides: 25 mm linear rails
- Motors: NEMA 34 steppers
- Spindle cooling: air
- Homing: inductive sensors
- Power: 220V
The machine moves along three axes:
- X — left/right
- Y — front/back
- Z — up/down
We controlled it with Universal G-code Sender (UGS), an open-source program that sends G-code to the machine, lets you jog the axes manually, and shows job progress in real time.
Safety Rules¶
These safety rules were clearly explained by the instructors at Fab Lab Dilijan during the Fab Academy program, and honestly, after seeing how powerful these machines are, none of them felt like overkill.
A CNC machine moves fast, spins hard, and doesn’t know the difference between wood and a careless hand. So before anyone touches the machine, the basics have to be second nature.
Personal Protective Equipment¶
- wear safety glasses
- tie long hair back
- avoid loose clothing
- remove jewelry
Material Fixing¶
The material has to be firmly fixed using clamps or screws before the spindle ever turns on. A loose piece of wood at high spindle speed is not something you want to find out the hard way.
Tool Check¶
Before machining starts, the tool itself needs to be checked — properly seated, properly tightened, and the right tool for the job.
Emergency Stop¶
Always know exactly where the Emergency Stop button is before you start. You don’t want to be looking for it once something goes wrong.
What is a CNC Milling Machine¶
A CNC milling machine (Computer Numerical Control) is a computer-controlled fabrication machine used for cutting and shaping materials with high precision.
Instead of a person guiding the cutting head by hand, the machine follows instructions written in G-code — basically a list of exact coordinates and movements that tells the spindle where to go, how fast, and how deep.
Material is removed using a rotating cutting tool called an end mill, which physically carves the shape out of the stock material, layer by layer if needed.
CNC milling machines can process a wide range of materials, including:
- Wood
- Plywood
- MDF
- Plastics
- Foam
- Aluminum
What makes CNC machining genuinely useful in a fab lab context is that it’s accurate and repeatable — once the toolpath is right, you can cut the same part ten times and get the same result ten times, something that’s basically impossible by hand.
CNC Workflow¶
The whole process, from idea to finished part, follows a clear chain:
FreeCAD → Aspire 9.5 → G-code → UGS CNC → CNC Milling
1. CAD Design¶
Everything starts with a digital design, built in CAD software. This is where the actual geometry of the part gets defined.
2. CAM Toolpath¶
Once the design is ready, it gets imported into CAM software, where the toolpaths are generated — basically the path the cutting tool will physically follow.
A few parameters matter a lot here:
- cutting depth
- feed rate
- spindle speed
- tool selection
3. G-code Generation¶
After the toolpath is set, the CAM software translates everything into G-code, the actual instructions the machine will read.
4. Sending File to CNC¶
The G-code file then gets sent to the machine using UGS CNC, which handles the communication between the computer and the CNC.
CNC Software¶
This week we worked with two important programs.
Aspire 9.5¶
Aspire 9.5 is the software we used to prepare machining operations and generate toolpaths from the design.
With Aspire we can:
- define material thickness
- select the cutting tool
- define feed rate and spindle speed
- generate toolpaths
- export G-code
UGS CNC (Open-Source Software)¶
UGS CNC (Universal G-code Sender) is an open-source program used to communicate with CNC machines — it’s the bridge between the G-code file and the physical motors.
With UGS we can:
- send G-code to the machine
- control axis movement manually
- monitor the job in real time
- start or stop machining
CNC Cutting Tools¶
CNC machines use different cutting tools, generally called end mills, and each one is suited to a different kind of cut.
Flat End Mill Used for flat surfaces and general cutting.
Ball Nose End Mill Used for curved surfaces and 3D machining.
V-Bit Used for engraving.
Compression Bit Used for cutting plywood with clean edges on both the top and bottom surface.
Feeds and Speeds¶
Two parameters that can make or break a job:
Feed Rate — the speed at which the tool moves through the material. Spindle Speed — how fast the tool itself is spinning.
Get these wrong, and the consequences show up fast:
- tool breakage
- burned material
- poor surface quality
Individual assignment¶
After learning about CNC machining and going through the safety procedures, I moved on to my individual assignment.
The design was created in FreeCAD.
My goal was to design a chair assembled entirely using press-fit joints — no screws, no glue, no extra hardware. Just the geometry of the parts holding everything together.
This meant the joints had to match the exact thickness of the material, since even a small mismatch would make the parts too loose or too tight to assemble.
Chair design in FreeCAD.
G-code Generation¶
Once the model was finished in FreeCAD, I imported the design into Aspire 9.5.
In Aspire I:
- defined the material thickness
- selected the cutting tool
- created the toolpaths
- generated the G-code
Figure 18 — Toolpath generation.
CNC Machine Setup¶
Before starting the actual machining, the machine itself had to be prepared.
Steps included:
- installing the cutting tool
- preparing the machine bed
- setting the X, Y, Z origin
Milling Process¶
Once setup was complete, the G-code was loaded into UGS CNC and the machining process began.
Final Result¶
After machining, the chair parts were finally ready — and seeing the press-fit joints actually click together without a single screw was genuinely satisfying.
The parts were designed using press-fit joints, allowing the whole chair to be assembled without screws or glue.
Final CNC cut parts.
Learning Outcome¶
During this week I learned:
- CNC machine fundamentals
- the digital fabrication workflow from design to physical part
- Aspire 9.5 toolpath generation
- UGS CNC machine control
- cutting tools and machining parameters
- CNC safety procedures, both individual and on a much larger machine in Gyumri
This week helped me understand CNC machining as a complete digital fabrication process connecting design, software, machine control, and physical manufacturing — and seeing both a small-scale and a large-format machine in the same week made it clear how much these principles scale, even when the hardware itself looks completely different.