Computer-Controlled Machining¶
This week’s goal was to complete lab safety training, test the design rules and machining parameters of our CNC machines as a group), and individually design, mill, and assemble a meter-scale object.
Introduction¶
CNC machining is a widely used manufacturing process in which material is removed from a workpiece using computer-controlled cutting tools. In contrast to additive manufacturing methods such as 3D printing, CNC machining belongs to the category of subtractive manufacturing.
Instead of building an object layer by layer, the desired geometry is created by removing excess material from a solid block.
Modern CNC machines translate digital design files into precise tool movements along multiple axes. This allows complex geometries to be manufactured with high accuracy and repeatability.
Because of this precision and reliability, CNC machining is commonly used in prototyping, industrial manufacturing, and engineering applications.
For this assignment, the focus was not only on producing a part but also on understanding the workflow from digital design to machine operation and the physical limitations that influence the manufacturing process.
Subtractive manufacturing introduces several challenges that must be considered already during the design phase. Since the material is removed using cutting tools, the geometry of the tool directly limits which shapes can be produced.
Internal corners, for example, cannot be perfectly sharp because milling tools have a circular cutting edge.
Another important constraint is tool accessibility. The cutting tool must be able to physically reach every area that needs to be machined. This means that deep cavities, narrow slots, or complex undercuts can be difficult or impossible to produce depending on the available tooling and machine axes.
Material properties also influence the machining process. Hard materials require slower feed rates and can increase tool wear, while softer materials may deform or produce unstable cuts if machining parameters are not chosen carefully.
Because of these limitations, good CNC design requires a balance between the desired geometry and the practical constraints of the machining process.
Energy-Aware Manufacturing¶
In CNC machining, Energy-Aware Manufacturing can involve optimizing tool paths, reducing unnecessary machine movements, and selecting appropriate machining parameters.
Shorter machining times generally result in lower energy usage because the machine spindle, motors (and cooling systems) operate for a shorter period. Efficient toolpath strategies can therefore reduce both production time and overall energy demand.
Material efficiency also plays an important role. Since subtractive manufacturing removes material from a larger block, a significant amount of waste material can be produced. I therefore positioned the parts as closely as possible on the stock material and planned the machining layout carefully to minimize material waste. Careful planning of the initial stock size and machining strategy can help minimize this waste.
In the context of this assignment, the main focus was on the machining workflow rather than performing a fully optimized energy analysis. However, the concept of Energy-Aware Manufacturing highlights the importance of considering efficiency and sustainability when planning manufacturing processes.
Toolpath generation and CAM workflow¶
After designing a 3D model of the desired part, the next step is to prepare the machining process using the CAM environment in Autodesk Fusion. In this step, the digital geometry is translated into machine instructions that define how the cutting tool moves through the material.
Fusion allows different machining strategies to generate toolpaths depending on the geometry and the desired surface quality. Each strategy follows a specific logic for removing material, for example clearing larger areas, finishing surfaces, or machining contours.
During this stage, parameters such as tool type, spindle speed, feed rate, and step-over distance are defined. Based on these settings, the CAM software calculates the tool movements and generates a simulation of the machining process.
Once the toolpaths are verified and optimized, they can be exported as G-code, which contains the commands used by the CNC machine to perform the machining operation.
After importing the tool libary and post processor, the first step in the CAM workflow is creating a Setup.
In this step the workpiece and the machining environment are defined. This includes selecting the part that should be machined, defining the size of the raw stock material, and placing the coordinate system.
The coordinate system determines the origin point from which the CNC machine interprets all movements. Therefore, it is important to place it in a logical and accessible position, typically on a corner or the top surface of the stock material.
Once the setup is defined, different toolpath strategies can be selected. Fusion provides several categories of machining strategies, including 2D operations, drilling operations, and 3D machining strategies.
The 2D Pocket toolpath is used to remove material inside a closed boundary. The tool clears the interior area layer by layer until the defined depth is reached.
This strategy is commonly used to create cavities, recesses, or flat-bottom pockets.
Fusion automatically calculates multiple passes to gradually remove the material while maintaining stable cutting conditions. The remaining material is removed in several step-down layers to avoid excessive load on the cutting tool.
The 2D Contour toolpath follows the outline of a selected geometry. Instead of clearing an area, the tool moves along the boundary of the part to cut the final outer shape.
This strategy is typically used for cutting the final profile of a part or separating it from the stock material. Multiple depth passes are usually required until the full material thickness is reached.
The Slot toolpath is used to machine narrow channels where the tool width is similar to the slot width. The tool moves directly along the center of the slot to remove the material.
This strategy is commonly used for grooves, mechanical guides, or features that require a consistent width.
Because the tool cuts with its full diameter, cutting parameters must be chosen carefully to avoid excessive tool load.
Bore milling is used to create circular holes using a milling tool instead of a drill. The tool moves in a circular path and gradually enlarges the hole until the final diameter is reached.
This method is useful when the desired hole diameter is larger than the available drill bits or when higher positional accuracy is required.
The Drilling toolpath is used when holes are produced with a dedicated drill bit. The tool moves vertically into the material at predefined positions.
Fusion allows different drilling strategies such as simple drilling, peck drilling, or chip-breaking cycles. These strategies help remove chips and reduce heat during deeper drilling operations.
3D Adaptive Clearing is a roughing strategy designed to efficiently remove large amounts of material. The toolpath continuously adapts to the remaining geometry and maintains a constant tool load.
Instead of cutting the entire width of the tool, the algorithm calculates smooth paths that keep the engagement angle consistent.
This results in more efficient machining, reduced tool wear, and faster material removal compared to traditional roughing strategies.
The Parallel toolpath is a finishing strategy used for machining curved or complex 3D surfaces. The tool moves in parallel lines across the surface of the model.
This strategy is commonly used for finishing passes because it produces a relatively smooth surface finish.
The distance between the tool passes, known as the step-over, determines the final surface quality.
Although the individual toolpaths may differ depending on the machining strategy, many parameters remain similar across different operations.
One of the most important parameter groups in CNC machining is speed and feeds. These values define how fast the cutting tool rotates and how quickly it moves through the material.
The spindle speed determines how fast the tool rotates, while the feed rate describes how fast the tool moves along the programmed toolpath.
Together, these parameters define how aggressively the tool cuts into the material. If the values are too high, the tool can overheat, break, or produce poor surface quality.
If they are too low, the machining process becomes inefficient and can also negatively affect the cutting process.
To determine suitable values, it is important to consult the tool manufacturer’s datasheet.
Tool manufacturers usually provide recommended spindle speeds, feed rates, and cutting depths depending on the tool diameter and the material being machined.
These recommendations serve as a starting point and can later be adjusted depending on the machine capabilities and the machining results.
In practice, speed and feed settings are therefore a balance between theoretical recommendations, machine limitations, and practical experience gained during machining.
For every operation, several basic settings must be defined.
First, a geometry has to be selected, such as a contour, a pocket boundary, or a machining surface.
Next, the correct cutting tool must be chosen from the tool library. The tool defines parameters such as diameter, flute length, and maximum cutting depth.
Another important part is defining the heights. These settings determine how the tool moves vertically during the machining process, including safe heights, retract heights, and the final cutting depth.
Additional settings include selecting the appropriate coolant strategy, adding workholding components such as clamps or fixtures, and adjusting the overall machining tolerance.
These parameters help ensure that the simulation and the real machining process accurately reflect the physical setup.
While many parameters are fixed for safety and machining stability, other settings remain flexible.
For example, tabs can be added to contour operations to prevent the workpiece from becoming loose during the final cutting pass. These small bridges keep the part attached to the stock material until the machining process is finished.
Before exporting the machine code, it is recommended to simulate the complete machining process.
To do this, right-click on the setup and select Simulate. The simulation visualizes the entire machining operation and helps detect potential problems.
If no red bars appear in the timeline, there are no detected collisions. The simulation also allows checking whether the toolpaths behave as expected and if adjustments are necessary.
After verifying the simulation, the NC code can be generated. Again, right-click on the setup and select Post Process. In the post processor settings, I selected EAS GmbH as the post processor.
Then enter a file name and choose the desired storage location.
Finally, confirm the export to generate the G-code file. This file contains the machine instructions used by the CNC machine to perform the machining process.
Safety training¶
When working with a CNC machine, I paid close attention to safety procedures, since the process involves fast rotating tools and moving machine parts.
Before starting the milling process, I checked that the workpiece was properly fixed to the machine bed and that the tool was correctly mounted in the spindle.
I also ensured that the workspace around the machine was clear and that no loose objects were present near the moving parts.
During machining, I stayed close to the machine and continuously monitored the process.
CNC machines should never be left unattended while running, since unexpected tool behavior, incorrect toolpaths, or loose workpieces can occur.
I wore safety glasses during operation to protect against chips and debris generated during machining. Additionally, emergency stop buttons must always remain accessible in case the machine needs to be stopped immediately.
CNC machine¶
For this assignment I used the Versatil 2500 CNC milling machine manufactured by EAS GmbH. The machine is designed for machining large sheet materials such as wood, MDF, or plastic panels.
The machine has a working area of 2500 mm × 1250 mm, which corresponds to the standard sheet size used in many fabrication environments.
According to the manufacturer’s specifications, the machine provides a maximum positioning error of ±0.1 mm and a repeatability of ±0.05 mm.
The machine is operated using the software NC-EAS(Y) PRO, which interprets the generated G-code and controls the machine movements. Tool libraries for the available milling cutters are provided by the producer.
The resulting files are exported in the .nc format and then loaded into the machine control software.
A vacuum table is used to fix larger workpieces during machining. Before starting the milling process, the two rotary switches on the left side of the machine must be activated. When the red switches are in the vertical position, the vacuum system is turned on and the workpiece is held in place by suction.
For smaller parts, especially pieces smaller than approximately DIN A2, the vacuum alone is often not sufficient. In this case the workpiece must additionally be fixed using screws. The sacrificial board on the machine is 9 mm thick and made from MDF. MDF is suitable as a sacrificial layer because it is porous and therefore allows air to pass through the material, which supports the vacuum fixation system. The edges of the board are sealed with a special coating to maintain proper vacuum performance.
Final project prototype¶
For my final project, I designed a floor lamp with an integrated lighting system.
Before building the final version, I wanted to get a first impression of the overall proportions and the physical dimensions of the design.
Therefore, I produced an initial prototype using the CNC machine.
The goal of this prototype was not to create the final product, but to evaluate the general shape, scale, and structural stability of the lamp design.
Since this was only an early prototype, I focused on minimizing material waste and machining time. The parts were therefore simplified and optimized for quick production.
This allowed me to quickly verify whether the design concept works in real life and whether adjustments to the geometry might be necessary before producing the final version.
Finished 3D model of the lamp used for the CNC machining process.
The joint extends into the lamp base to create a stable connection between the vertical element and the base.
CAM setup for the machining process. The coordinate system is placed at the lower corner of the stock material.
I first used the 2D contour toolpath.
Geometry settings.
Then I selected the contour geometry.
Here I defined the height settings. I only milled halfway through the material so I could later use a second tool. This helps reduce tear-out in the wood.
In this step I configured the pass settings and enabled multiple depth passes.
I set the multiple depth value to 3.1 mm, since the cutting depth should generally not exceed half of the tool diameter.
Here I adjusted the linking settings, including lead-in and lead-out movements and the tool positioning.
This shows the tool settings for the second contour operation, where I selected a different milling cutter.
Here I added small tabs to keep the workpiece securely attached to the stock during machining.
In this step I defined the height settings for the second operation, which now cuts from the halfway point down to the final depth.
The simulation showed no errors or collisions.
Then I exported the NC code.
I milled a small pocket into the center of the base. The final shape will later be refined manually with a chisel.
This simulation shows the pocket operation. I split the process into two tools, first using T3 and then T4, and the simulation confirmed that everything works as expected.
This is the EAS Versatil 2500 CNC machine.
With 8 tool holders.
And a vacuum table.
I first used a 12mm multiplex sheet (birch).
I loaded the file and placed it correcly in the program. Then I activated the vacuum.
After a last extra safety check I started the machine.
Small table¶
As a second project, I produced a small wooden table to experiment with different joinery concepts. The goal of this project was to test simple but stable connections between the tabletop and the legs.
In the first version, each leg was connected to the tabletop using a single continuous rectangular tenon.
This approach creates a strong mechanical connection because the tenon passes through the tabletop and distributes the load over a larger area.
In a second version, the connection was implemented using two cylindrical dowel-like tenons per leg.
This design requires more precise alignment but can simplify the assembly process and reduce the amount of material removed from the tabletop.
By comparing both approaches, I was able to evaluate how different joint designs influence stability, manufacturability, and assembly.
This was my design.
I arranged the parts.
I simply used 1 tool with a 2D Contour toolpath for the legs.
I used T5 loaded with a smaller milling cutter for the pockets and for the the standart T3 6mm drill for the contour.
I exported the NC codes, did the same workflow as mentioned earlier and started with the 8 legs in 12mm multiplex.
Then I used a 18mm sheet to cut the 2 tabletops.
After short sanding I assembled the first version and started with the round joints.
And assembled it.
Now everything can be oiled, sanded again and oiled again for perfect finishing.
Easter bunny¶
Since Easter is approaching, our social media team approached me with the idea of producing a small CNC-milled Easter bunny for promotional purposes.
To start the project, I downloaded a suitable STL model from an online repository and imported it into Fusion.
Because CNC machining works differently from additive manufacturing, I first simplified the mesh and split the model in half to make it easier to machine.
After preparing the geometry, I created the CAM setup and used 3D Adaptive Clearing as the main roughing strategy to remove the material efficiently.
One of the main challenges during machining was fixing the bunny securely to the machine bed. Because the geometry was relatively small and irregular, the vacuum table alone was not sufficient.
I solved this problem by fixing the workpiece with two screws during machining. To do this, I temporarily paused the machine, inserted the screws, and continued the milling process afterward.
The screw holes were later filled with wood filler to restore the surface appearance of the model.
lowpoly modern bunny - 3D viewer
Stay tuned for easter! I will post the video then.
Downloads¶
lamp_v1.step
table.step
easterbunny.step