Week 7 - Computer-Controlled Machining¶
This week, we officially began to engage with Computer Numerical Control \(CNC\) Milling. CNC machining is the core component of realizing physical production in digital manufacturing projects - from CAD model design to CAM programming, and then to the actual cutting process on machine tools, all of which rely on a mastery of the operating specifications, machining processes, and safety procedures of CNC milling machines.
**Group assignment: **
Understand the safety regulations and basic information of CNC milling machine processing from an overall perspective. For example, the basic parameters and characteristics of CNC milling machines, the content of operation security training, the machine pre-inspection process, environmental and material safety requirements, and the \"safety rules\" during the operation process. Through systematic learning and practice, establish a comprehensive understanding of CNC machining safety and machine tool basics, and build a solid safety defense line for subsequent actual machining operations.
**Individual assignment: **
Taking CNC milling of chairs as the project objective, complete the full-process practice from design to finished product. First, assign individual tasks, then use OnShape to complete the CAD model design of the chair, including the structural design of the seat and legs, size adjustment and tolerance adaptation, as well as the structural optimization of tenon-and-mortise joints \(T\-bone/dog bone\); then generate DXF cutting files and conduct process planning, use MasterCam X6 to generate the G-code required for machining, complete G-code conversion and machining simulation verification; then carry out the actual machining operation of CNC milling, and finally complete the assembly and effect display of the finished product.
Overall, the focus of this week is not to complete high-precision complex machining projects, but to establish a basic understanding of the entire process of CNC milling machining, including how to comply with machining safety regulations, how to use CAD/CAM tools to complete the transformation from design to machining, and how to verify the feasibility of machining processes through simulation and actual operation. Through these basic exercises, a solid practical foundation will be laid for subsequent digital manufacturing and physical project development.
Group Assignment¶
Group Assignment Page: Week 7 — Group Assignment: Computer-Controlled Machining | FAB26 - ChaiHuo Makerspace 2026
1. CNC Milling Machine Information¶
This equipment is a dedicated CNC device for woodworking, capable of achieving automated carving, cutting, and milling operations, with high precision and efficiency. It is suitable for furniture production, woodworking design, and panel processing scenarios, and the working area is above 1300mm for the X-axis, 2500mm for the Y-axis, and 200mm for the Z-axis.
2. Security Training¶
During operation, strict personal protection must be ensured: safety glasses must be worn to prevent eye injuries caused by drill bit fragmentation and high-speed wood chip splashing; the operating noise of the equipment spindle and vacuum pump exceeds 85dB, so it is recommended to wear earplugs or earmuffs for hearing protection; when processing MDF materials containing glue and resin, N95 or higher level dust masks must be worn, and the dust removal system must be confirmed to be working properly; at the same time, jewelry, lanyards, and watches must be removed, long hair must be tied up, and long sleeves must be rolled up to avoid clothing being caught in the equipment and causing safety hazards.
3. Machine Pre-inspection¶
Three key inspection points before starting a CNC milling machine: manually move the spindle to clear the path and confirm that its operating trajectory will not collide with fixtures or the frame; ensure that the tool chuck is tightened properly to prevent the drill bit from loosening and flying out to cause injury during high-speed operation at 24,000 revolutions per minute; and remember the location of the red emergency stop button. Keep your hand close to the emergency stop button within the first 30 seconds of running a new program to facilitate quick shutdown in case of an emergency.
4. Environmental and Material Safety¶
Reviewed the environmental and material safety requirements for MDF board processing: MDF dust is flammable, and a slow feed rate can easily cause smoking or ignition due to friction. It is recommended to process at a speed of 5000 mm/min to ensure tool heat dissipation; during processing, it is strictly prohibited to hold the workpiece by hand. This time, 18 mm thick MDF boards are used, and the lateral impact force is relatively large when using an 8 mm tool, so it is necessary to ensure that the fixture is tightened; at the same time, it is necessary to keep the ground around the equipment free of debris and foreign objects to prevent operators from tripping.
5. The \"Golden Rule\" of Homework¶
This learning session has clearly defined three core safety guidelines for CNC milling machine operations: Do not leave the post without permission during the entire cutting process, as most CNC accidents occur when the operator briefly leaves the equipment; keep hands away from the table while the machine is running, and if it is necessary to point at the workpiece or equipment, use a tool for assistance, direct finger contact is prohibited; after the machining is completed, wait for the spindle to come to a complete stop before reaching out to remove the machined part, eliminating the risk of accidental contact.
Individual Assignment¶
1. Individual task assignment¶
This individual assignment involves creating a spliced MDF chair, independently completing the entire process from CAD model design, DXF cutting file creation, CAM path planning, G-code generation and conversion, to CNC milling and component assembly, ultimately resulting in a stable chair finished product with screwless splicing.
2. CAD Model Design \(OnShape\)¶
This chair design uses a mortise and tenon joint structure without screws, achieving the fixation of the seat and chair legs through a cross slot, and is modeled by dividing it into two major components: the seat and chair legs.
2.1 Seat Model Design¶
The seat surface includes two options: circular contour and square rounded corner contour, with a cross-shaped through groove reserved in the center for splicing and fixing with the tenon of the chair leg.
2.2 Design of Chair Leg Model¶
The chair legs adopt a symmetrical support structure, with the top designed with a tenon that matches the cross-slot of the chair seat, ensuring structural stability after splicing.
2.3 Dimension Adjustment and Tolerance Adaptation¶
Considering the machining allowance of 18mm thick MDF boards, the model dimensions are adjusted accordingly: the seat diameter/side length is 300mm, with a thickness of 18mm; the chair leg height is 250mm, with a thickness of 18mm; the splicing groove dimensions are adapted to the machining tolerance of 8mm tools, with a 0.1mm clearance reserved to ensure assembly compatibility.
2.4 Mortise and Tenon Joint Structure Design \(T\-Bone/Dog Bone\)¶
A standard dogbone \(Dogbone, i\.e\., T\-bone / dogbone\) structure is adopted at the corner of the splicing groove between the chair seat and chair legs. Since the CNC milling cutter is a circular tool, it cannot machine a perfect right angle, leaving rounded corners at the groove corners; this structure eliminates the rounded corners generated by tool machining by additionally machining an arc notch at the corner, allowing the mortise and tenon structure to fit perfectly and achieve seamless splicing. In the corresponding DXF cutting file, the four corners of the cross groove on the chair seat and the mating positions of the chair leg tenons have been designed according to this structure, fully matching the design logic.
3. DXF Cutting File and Process Planning¶
The DXF cutting file for this assignment includes the complete outlines of two types of chair seats \(round, square with rounded corners\) and their corresponding chair legs, has completed layout optimization, and can be directly imported into MasterCam for path planning.
This machining uses an 8mm flat end mill and is completed in two steps: roughing and finishing. The process parameters are as follows:
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Spindle speed: 24000 RPM
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Feed rate: 5000 mm/min
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Processing sequence: First process the cross slot and contour of the chair seat, then process the tenon of the chair leg and the support contour
4. MasterCam X6 G-code Generation¶
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Import the DXF cutting file and set the workpiece coordinate system and tool path in MasterCam X6.
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Set the contour milling paths for the seat and chair legs respectively, simulate the tool movement trajectory, and ensure there are no overcutting or collision issues.
5. G-code Conversion and Machining Simulation¶
First, import the G-code generated by MasterCam into the CNC milling machine control system, and complete the adaptation and conversion of the code according to the machine tool\'s control protocol and format requirements to ensure that the instruction format and parameter definitions are compatible with the machine tool. Subsequently, run machining simulation in the milling machine control system to verify the syntax logic and machining path of the G-code throughout the process, check whether there are collisions, overcuts, or abnormal paths in the tool path, confirm the rationality and safety of the machining actions, and eliminate potential risks for actual machining.
6. CNC Milling Process¶
After completing the preliminary G-code conversion and machining simulation verification, the process enters the CNC milling stage, where equipment preparation and actual machining operations are carried out according to standardized procedures to ensure machining accuracy and process safety.
- Pre-processing Preparation: Install and secure the 8mm flat-bottom milling cutter, check the status of the spindle and dust collection system, and fix the MDF board on the workbench.
- Processing Procedure: Start the equipment, process the seat and chair leg components sequentially according to the preset path, and monitor the processing status throughout to ensure no abnormalities.
- Post-processing after machining: After the spindle has completely stopped, remove the machined part and clean up wood chips and burrs.
7. Product Assembly and Effect Display¶
The finished chair seat and chair legs are assembled by cross-slot splicing, forming a stable chair structure without the need for additional fasteners.
[!NOTE]
AI Assistance：
During the preparation of this documentation, ChatGPT (GPT-4) was used as a language assistance tool.
It helped with sentence polishing and translation from Chinese to English to improve readability and clarity.