Mechanical Design, Machine Design

For week 12 of Fab Academy, my team and I decided to build a custom CNC machine designed to engrave screen-printed stamps onto metal plates.

Within the collaborative project, my primary responsibility was the design and fabrication of the machine's mechanical system. Since metal engraving and scratching require considerable cutting force, I designed the motion transmission system using ball screws to ensure the necessary mechanical advantage and thrust. To achieve the required structural rigidity while maintaining the build's modularity, I constructed the main frame using aluminum extrusion profiles combined with custom 3D-printed joints and supports.

CAD Design

In the following carousel, I have arranged images of the main components that I designed and manufactured for the mechanical system.

Lower Union by oski._.hgez on Sketchfab

Lower Union

This custom 3D-printed joint is designed to connect three aluminum extrusion profiles at 90-degree angles, forming the corners of the CNC machine's main frame. It features square slots that perfectly align with the extrusions to ensure structural squareness.

Furthermore, it incorporates side mounting holes for screws that secure the profiles, preventing any slippage or vibration during the engraving process. Its reinforced base also provides stable support for the entire structure.

Higher Union by oski._.hgez on Sketchfab

Higher Union

This 3D-printed top joint connects the vertical uprights to the horizontal top frame. It maintains the same female socket design and side screw holes for securely attaching the aluminum extrusions. By rigidly joining the top axes, this component is crucial for preventing twisting and structural buckling. It ensures the machine frame remains perfectly square and stable, even when the engraving tool applies strong lateral forces to the metal plates.

Y-axis Motor Mount by oski._.hgez on Sketchfab

Y-axis Motor Mount

This 3D-printed component is a crucial connection point for the Y-axis drive system. Its primary function is to securely mount the stepper motor. It also incorporates a precise cylindrical housing for anchoring the linear guide, ensuring smooth and accurate axis movement. Integrated mounting tabs allow the entire assembly to be firmly bolted to the aluminum extrusion frame, connecting the motion system directly to the machine's rigid structure.

X-axis Motor Mount by oski._.hgez on Sketchfab

X-axis Motor Mount

This part acted as the crucial bridge between the machine's X and Y axes. I designed it to securely hold the X-axis stepper motor while simultaneously moving along the Y-axis drive system.

It features two perfectly aligned cylindrical holes for anchoring the dual linear guides, providing a smooth and stable path for the engraving carriage.

Car with Motor by oski._.hgez on Sketchfab

Car with Motor

For the vertical control of the machine, I designed this component to house the Z-axis stepper motor, which is directly responsible for raising and lowering the engraving tool. I incorporated parallel cylindrical channels to securely guide the vertical linear rods, ensuring precise and stable up-and-down motion.

This design choice minimizes leverage and eliminates any play or deflection that could compromise the final engraving quality.

Car with Tool by oski._.hgez on Sketchfab

Car with Tool

As the final active component of the Z-axis, I designed this carriage to firmly hold the engraving tool as it moves up and down. Since our scoring process required the tool to maintain a specific orientation relative to its path, I integrated a custom housing for a servo motor and a dual-gear drive system. This configuration allowed the machine to actively rotate the tool, keeping it perfectly aligned to the direction of movement at all times. Incorporating this mechanism was critical to achieving clean, precise scoring on the metal plates without lateral tool drag.

CNC STL Parts

Demonstration

Gear

To complete the tangential control mechanism, I assembled a custom 90-degree bevel gear transmission.

Gear Type: Bevel Gears 90-degree

Module: 2

Driving Gear (Servo): 20 Teeth

Driven Pinion (Tool): 18 Teeth

Complete Assembly

Once all the individual components were designed, I created a complete 3D assembly of the entire CNC machine. This step allowed me to check the overall alignment, make sure all the parts fit together perfectly, and check for physical interference between the moving axles. By visualizing the completed mechanism in the software, I was able to confidently determine if any final design modifications were necessary before moving forward with 3D printing and physical fabrication.

Prototyping and Tolerance Testing

Before spending time and materials printing all the structural components, I first 3D printed a single bottom corner joint to serve as a test piece. It was crucial to physically verify its functionality and check the actual tolerances with the aluminum extrusions. Once I tested the fit, I realized it was necessary to set a tolerance of 0.2 mm, so I modified the 3D models to implement this change. With the updated designs ready, I proceeded to print all the remaining parts.

Assembling the CNC

To keep the project organized and replicable, I compiled a comprehensive Bill of Materials. It is divided into off-the-shelf components that were purchased and custom parts that were fabricated in the lab.

Purchased Components (Off-the-shelf)

Qty	Component	Description / Specs
4	NEMA Stepper Motors	For X, Y, and Z axis movement
4	Flexible Couplers	Connects NEMA motor shafts to the lead screws
8	Aluminum Extrusion Profiles	Main structural frame. Cut lengths: 4x 300 mm and 4x 190 mm
4	Square Tubing	Additional structural support. Cut lengths: 4x 300 mm
6	Linear Guide Rods	Smooth steel rods. Cut lengths: 2x 305 mm, 1x 292 mm, 1x 260 mm, and 2x 87 mm
4	Lead Screws	Threaded rods for motion. Cut lengths: 2x 320 mm, 1x 272 mm, and 1x 75 mm
4	Brass Lead Screw Nuts	Couples the carriage to the lead screw
6	Linear Bearings	For smooth travel along the guide rods
4	Mounted Bearings with Set Screws	To securely hold the ends of the lead screws
32	M4 x 6mm Screws	Fasteners
20	M4 x 10mm Screws	Fasteners
12	M3 x 8mm Screws	Fasteners
8	M3 x 16mm Screws	Fasteners
16	M3 x 30mm Screws	Fasteners
#	Respective nuts for each screw	Fasteners

Fabricated Components

Qty	Component	Process / Material
1 Set	Custom Joints, and Motor Mounts	3D Printed (PLA)
1 Set	X, Y, and Z Axis Carriages	3D Printed (PLA)
1	Machine Bed	Cut MDF & Plywood
4	Workholding Clamps	Fabricated Metal

I began the physical assembly from the ground up, starting with the bottom base frame. I carefully measured all the sides formed by the aluminum extrusions to ensure the base was perfectly square and true.
Next, I focused on assembling the vertical uprights along with their respective motor mount components.
At this stage, I also integrated the sliding carriages and the linear guide rods into the columns.
Once these vertical sub-assemblies were ready, I securely fastened them to the bottom base frame.
Finally, I constructed the top square frame and bolted it to the columns, completely tying the structure together to achieve maximum rigidity.

During the assembly process, specifically when integrating the X-axis, I noticed that the carriage wobbled and lacked stability with only one support. I realized that adding a second parallel guide was essential to avoid this balance problem. Implementing this crucial modification ensured that the gantry had the rigid and perfectly linear movement necessary for engraving metal without any tool deflection.

As seen in the image, the initial carriage was supported by only a single guide rod and the drive screw. To resolve the wobbling issue, I updated the 3D model by adding a second parallel guide rod, positioning the screw symmetrically in the middle of the two supports.

With this problem solved, I set about assembling the bed where the boards would be located. For this, I decided to use MDF and plywood, and I drilled holes to attach it to the profile structure.

To secure the metal plates to the machine bed, I fabricated custom metal clamps. These clamps were designed to be adjusted using a screw system, providing firm, adjustable pressure that keeps the workpiece perfectly still. Implementing this clamping mechanism was crucial to prevent any movement or vibration during the high-force engraving process, thus ensuring a clean and precise finish on the metal surface.

To wrap up the mechanical build, I performed a final pass over the entire structure, securely tightening all the fasteners to guarantee maximum rigidity. Below is the final result of the fully assembled CNC machine: