Low-Cost CNC Milling Machine with Continuity Sensor

Team: Manuel Ayala-Chauvin, Sandra Nuñez-Torres
Institution: Fablab - Universidad Tecnológica Indoamérica
Year: 2025

---

---

Project Overview

This project aimed to design, build, and automate a low-cost CNC milling machine equipped with a continuity sensor to map surface profiles on copper plates. By applying a concurrent engineering approach, the team simultaneously developed the mechanical, electronic, and software systems to achieve a modular, affordable, and replicable machine for educational and research environments.

---

Mechanical Design (Part 1) — Group Assignment

Machine Concept

The machine was conceived as a three-axis Cartesian CNC with a leadscrew drive system, capable of manual and automated operation. The design prioritized low-cost materials, ease of fabrication, modularity for future upgrades, and sufficient precision for contour line generation.

Mechanical Design and Manual Testing

The frame was built using aluminum profiles and AISI 1020 steel reinforcements. Movement was guided by linear rails (12 mm) and driven by 8 mm leadscrews with a 2 mm pitch. Before installing electronics, the machine was manually operated via hand cranks to validate mechanical alignment, smoothness of motion, and structural rigidity. FEA simulations predicted a maximum displacement of 0.0236 mm under load, which manual testing later confirmed as acceptable.

Methodology

The mechanical design was based on a four-stage method:

1. Requirements: Define specifications based on cost, flexibility, modularity, and precision.
2. Conceptual Design: Modeled in SolidWorks; determined structure, actuation, and materials.
3. Detailed Design: Generated CAD files, FEA simulations to validate structure.
4. Prototype Fabrication: Built physical structure with aluminum profiles and AISI 1020 steel reinforcements.

The diagram presents the systematic design process used for the low-cost CNC milling machine project. It begins with the identification of technical specifications, which define the project's fundamental requirements such as work area dimensions, desired precision, and operational capacity. The next step involves conceptual design, focusing on selecting suitable motion systems like leadscrews and motors. A bibliographic study of existing CNC technologies is conducted in parallel to enrich the conceptual framework. Once the preliminary design is ready, a technical and economic feasibility study is carried out to evaluate material availability and budget constraints. If materials are not obtainable within the project’s context, the process loops back to redefine specifications and adjust the design accordingly. When feasibility is confirmed, the project advances to the detailed design phase, generating complete CAD models, technical drawings, and part lists. The final stage is the materialization phase, where the prototype is constructed based on the finalized plans. This iterative and feedback-driven process ensures the CNC machine is not only functional and efficient but also economically viable and adaptable to local fabrication capabilities.

Group Collaboration

• Manuel focused on mechanical design, material selection, and manual assembly.
• Sandra designed the usability aspects, including form factor, accessibility, and ergonomic considerations.

---

Mechanical Design (Part 1) — Individual Assignment

Manuel Ayala-Chauvin

• Developed full SolidWorks CAD models for frame, motion, and assembly systems.
• Performed mechanical dynamic calculations to select actuators.
• Manually fabricated and assembled mechanical systems, aligning and calibrating axes.

1. Development of Full SolidWorks CAD Models for Frame, Motion, and Assembly Systems

As the mechanical design leader, Manuel was responsible for creating detailed three-dimensional CAD models of the entire CNC milling machine using SolidWorks. This work included modeling the primary structure (frames and supports), the motion transmission system (leadscrews, couplings, linear guides), and the mechanical subassemblies (motor mounts, sensor holders, spindle supports). Each component was designed parametrically to allow for easy adjustments and scalability. The modeling process ensured that interferences were minimized, tolerances were respected, and that future modifications, such as enlarging the working area or integrating new actuators, could be accomplished efficiently. Additionally, the CAD models served as the basis for generating technical drawings for fabrication and assembly documentation.

This screenshot shows the complete CAD model of the machine developed in SolidWorks. The left sidebar lists each component and subassembly, such as motors, rods, and bearings. It demonstrates that the project followed good parametric modeling practices, ensuring easy modifications or scaling of the machine. The final 3D design confirms that all motion systems are correctly aligned and mechanically feasible.

2. Performance of Mechanical Dynamic Calculations to Select Actuators

Manuel conducted comprehensive mechanical analyses to determine the necessary force and torque requirements for each axis movement. Using basic dynamic and static formulas, he calculated the load requirements based on the weight of moving elements, friction coefficients, and desired acceleration values. Based on these calculations:

• The maximum required force to move the system was estimated at 12.45 N.
• The corresponding required torque was calculated at 0.00396 Nm.

Given these results, he selected NEMA 17 stepper motors (rated at 0.3 Nm torque) to provide a safety margin greater than 6 times the calculated needs. This approach ensured that the motors could handle not only the operational forces but also unexpected resistance during prolonged usage, enhancing the machine’s reliability and operational lifetime.

3. Manual Fabrication and Assembly of Mechanical Systems, Alignment and Calibration of Axes

After the fabrication of individual parts, Manuel personally led the mechanical assembly of the CNC machine. This process required careful squaring and alignment of the frame, precision positioning of the linear rails, and exact installation of leadscrews and bearings. Mechanical calibration was critical: each axis was manually moved and adjusted to eliminate excessive friction, misalignment, or backlash. Dial indicators, calipers, and alignment jigs were used to validate and correct the mechanical setup, ensuring smooth and accurate movement across all three axes (X, Y, and Z). These manual efforts directly contributed to the machine’s final precision during both manual and automated operations.

This image displays the fully assembled CNC milling machine ready for operation. It highlights the Dremel spindle mounted correctly, the bed aligned with X and Y axis movement, and the general structural stability of the design. The aluminum and steel frame ensures a balance between weight and rigidity, vital for precision scanning and machining tasks.

Sandra Nuñez Torres

• Designed the outer shell, operator interfaces, and panel arrangements.
• Validated user access to key components during manual operation.
• Documented usability testing during early mechanical validation phases.

1. Design of the Outer Shell, Operator Interfaces, and Panel Arrangements

One of the fundamental contributions was the design of the external structural elements that house and protect the CNC milling machine’s functional components. This included the development of an ergonomic and protective outer shell that minimizes external particle ingress, improves user safety, and optimizes aesthetics. Operator interfaces, such as emergency stop locations, manual access points for tool changes, and the positioning of control buttons, were carefully analyzed and incorporated. Additionally, the red rear protection panel was strategically designed not only to shield sensitive components but also to serve as a mounting platform for cable management and future electronics (controllers, sensors). The entire layout was modeled in SolidWorks to ensure seamless integration with the mechanical motion system without causing interferences.

This image shows an exploded view of the CNC milling machine, where each component is separated to visualize its positioning and assembly order. Key elements include the linear rails (8 and 9), leadscrews (1 and 5), spindle mount (11), rear frame (20 and 21), and the protective electronics panel (16). This view is essential to understand how parts fit together and how to proceed during assembly or maintenance.

2. Validation of User Access to Key Components During Manual Operation

Prior to the automation phase, manual validation of the CNC machine was critical. Sandra conducted a series of usability inspections to confirm that operators could comfortably access critical areas such as: - The spindle head (for tool attachment and maintenance), - The bed surface (for part loading and securing), - Leadscrew supports and guide rails (for maintenance and alignment verification). Adjustments were proposed and implemented, such as slight repositioning of the bed relative to the frame and additional clearances in the Z-axis structure, to enhance ease of use without compromising mechanical performance. These actions directly contributed to reducing setup and maintenance times, improving the overall machine usability.

3. Documentation of Usability Testing During Early Mechanical Validation

A systematic usability testing protocol was developed, involving practical walkthroughs of typical machine operations in a manual mode. Sandra documented ergonomic bottlenecks, safety hazards, and operator fatigue risks. Recommendations arising from this testing included: - The placement of cable routing away from operator access paths, - The suggestion of installing a transparent protective screen for moving parts, - Guidelines for labeling manual control interfaces clearly. These improvements were integrated into the second mechanical validation cycle and contributed substantially to enhancing the machine’s operational experience, particularly for new or non-expert users. All findings were archived in the project’s design documentation to inform future iterations or scalability projects.

---

Machine Design (Part 2) — Group Assignment

Actuation and Automation

The machine was automated by integrating three NEMA 17 stepper motors driven by DRV8825 drivers, controlled through an Arduino UNO with a CNC Shield. A fine-contact continuity sensor was connected to detect surface variations along the Z-axis. Toolpaths were generated using Vectric Aspire and executed with Universal G-Code Sender.

The image illustrates the electronic control system architecture implemented for the low-cost CNC milling machine. At the center of the system is an Arduino UNO, which serves as the main microcontroller, responsible for interpreting G-code commands and translating them into precise motion instructions. Mounted on top of the Arduino is a CNC Shield, which organizes and routes the electrical connections to the stepper motor drivers and limit switches. Four NEMA 17 stepper motors are connected: one motor controls the X-axis movement, one controls the Z-axis vertical movement, and two motors are connected to the Y-axis to ensure synchronized and stable motion of the machine bed. Each motor is powered and driven independently through the CNC Shield, allowing fine control over direction and steps. This modular setup ensures that the CNC machine can achieve high precision while maintaining a low-cost, open-source hardware base. The use of a CNC Shield simplifies wiring complexity and enhances system maintainability, making the machine more accessible to students, researchers, and DIY makers. Furthermore, the dual-motor configuration on the Y-axis significantly improves structural stability and alignment during fast movements, which is critical for maintaining milling accuracy. Overall, this configuration represents an efficient, scalable, and easily replicable solution for educational and small-scale manufacturing environments.

Testing after Automation

The automated system was tested over copper plates to verify contour mapping accuracy. Calibration of stepper motor steps/mm and sensor response ensured consistent scanning performance.

The figure shows the workflow used to machine any type of material on the low-cost CNC milling machine. The process begins by placing the material inside the machine and securely clamping it using holding systems. If the material is not properly fixed, adjustments must be made to ensure a firm hold, essential to prevent displacement during machining. Once secure clamping is verified, the toolpath is designed using Vectric Aspire software, where the cutting paths are defined. Subsequently, the vector design is converted into G-code using Universal G-Code Sender software, setting the movement parameters for the axes. Finally, the CNC machine automatically performs the machining operation on the secured material. This workflow ensures that all steps, from material preparation to final machining, are performed in a controlled and precise manner, guaranteeing high-quality results.

The image shows the CNC milling machine connected to a laptop controlling the machining process via CAM software. The CNC setup is ready to execute the loaded machining program.

This screenshot displays the programmed toolpaths in a spiral pattern. G-code commands are successfully processed, with X, Y, and Z axes settings visible, ensuring that the machine is ready for precise operation.

A detailed view of the G-code console shows each processed command. While most commands are confirmed as "ok", some errors such as error20 (tool change) are noted, demonstrating real-time system feedback.

A close-up image of the milling machine engraving a circular path onto an MDF sheet. The tool is visibly executing the programmed path, confirming correct translation from digital to physical.

This image shows the active execution of the machining process with live tracking of tool movements and processed commands, confirming real-time system monitoring.

A top view of the complete CNC workstation, including the machine, laptop, tools, and materials. This setup highlights the comprehensive preparation for digital fabrication operations.

Group Collaboration

• Manuel integrated electronics, programmed the Arduino, and developed G-code sequences.
• Sandra focused on usability and safety during automated operations, including layout optimizations for cables and user interface design.

---

Machine Design (Part 2) — Individual Assignment

Manuel Ayala-Chauvin

• Firmware Development: Programmed the Arduino firmware responsible for CNC motion control, integrating routines for the precise management of stepper motors and sensor feedback.
• Component Calibration: Calibrated stepper motors to ensure accurate displacements and adjusted the continuity sensor to guarantee precise surface detection during scanning processes.
• Testing and Optimization: Conducted complete testing cycles using G-code files, validating the correct interpretation of programmed paths. Subsequently optimized feedrate and acceleration parameters, achieving smoother performance and reducing mechanical wear on the machine.

Sandra Nuñez Torres

• Usability Documentation: Conducted detailed documentation of usability observations after automation implementation. Suggested ergonomic improvements aimed at facilitating operator interaction with the CNC, focusing on comfort and reducing fatigue risks.
• Participation in Automated Testing: Participated in automated system testing sessions, verifying both operator safety and workflow efficiency, ensuring that operational protocols met basic ergonomics and industrial safety standards.

---

Results and Analysis

Experimental Testing

• 100 surface scans were performed on copper plates (100x100 mm).
• Global Mean Error: 4.1%
• Standard Deviation: 0.5%
• Average Scan Time per Piece: 5.8 minutes

Cost Analysis

Component	Cost (USD)
Stepper Motors (3 units)	$60
Mechanical Components (guides, bearings, leadscrews)	$199
Electronic Components (Arduino, Shield, Drivers)	$198
Spindle (Dremel Tool)	$150
Fabrication Labor and Assembly	$400
Total	$1007

Notes: Bulk material sourcing could reduce overall costs by 10-15%.

---

---

Video Proof of Operation

Watch the video of operational testing here: https://youtu.be/TLGdXZf97eM

---

Conclusions

This project successfully demonstrated the viability of designing and constructing a low-cost CNC milling machine for contour mapping applications. Through meticulous mechanical design, careful component selection, and synchronized software development, a highly functional and accessible machine was built.

The collaboration between mechanical design and usability specialists ensured that both technical performance and user experience were addressed from the earliest stages. Future improvements will explore higher resolution sensing, faster scanning speeds, and extended machining capabilities.