Week 6: Large Format CNC (Computer Controlled Machining)¶
Objective:¶
Complete the assignments focusing on Large Format CNC, which include both individual and group tasks:
- Group Assignment:
- Perform a test on the CNC machine to identify the basic requirements and operations.
- Individual Assignment:
- Design a piece that can be assembled using press-fit techniques without any external materials and fit within a [1220 mm x 2440 mm x 12 mm] size wooden sheet.
- Cut the design using the CNC machine.
- Assemble the cut parts of the design.
Due to the large number of students in my batch, we were divided into three groups: CNC Machine, 3D Printing, and Mold & Casting. This allowed group members to gather information that would benefit them in their group final project.
Group Assignment: CNC Machine Testing¶
I was placed in the CNC Machine group, and to be honest, I couldn’t hold my excitement 🤩. For once, my own design could be brought to life—something I created on a computer would be in my hands. However, I felt slightly disappointed 😕 because I had to hurry and create something quickly, without the necessary time for my brain to generate something extraordinary. Something that would make my fellow students, my tutors, and especially my family, amazed by my creations. Unfortunately, I didn’t have enough time to come up with ideas that would make full use of this amazing opportunity. So, I turned to my mother to bring light into this situation, and, unsurprisingly, she had plenty of ideas! 😂 I’ll share those in the Individual Assignments section.
CNC Machine Overview:¶
The CNC machine we’re using is a large format machine capable of cutting wood sheets with a 6mm size cutting tool. The machine is connected to a computer where it receives commands on where, when, and how deep to cut, based on designs created in CAD software. The process involves generating toolpaths, which guide the cutting tool along the material, and controlling the spindle speed, feed rate, and depth of cut to ensure precision.
Safety Requirements:¶
Safety is paramount when working with CNC machines. Key safety requirements include:
- Safety Glasses: To protect eyes from debris and any accidents from the machine.
- Proper Clothing: Avoid loose clothing that could get caught in the machine.
- Inspection: Always inspect the machine and tools before use.
- Workplace Cleaning: Ensure the workspace is clean before and after machining.
- Hearing Protection: Although not provided to us, it’s extremely necessary.
- Emergency Button: Always know the location of the emergency stop button.
- Distance: Maintain a safe distance from the machine while it operates.
Debris Management:¶
The CNC machine is equipped with a vacuum system that sucks up debris generated during cutting. This is essential for maintaining a clean work environment and ensuring the accuracy of cuts.
Importance of Dogbones:¶
When designing joints, adding a dogbone is crucial. It allows for the square corners of the design to fit together snugly, accommodating the round cutting tool.
Material Alignment and Sacrificial Sheet:¶
Proper alignment of the material on the CNC bed is critical. We used a sacrificial sheet beneath the material to protect the machine bed and ensure clean cuts. The sacrificial sheet also helps in securing the material by screwing it down to prevent bending during cutting.
Materials Used:¶
We had two materials available: plywood and MDF. MDF (Medium Density Fiberboard) is smoother and easier to cut, but less strong than plywood, which has a more robust structure due to its layers. Our test was conducted on MDF, where we carefully adjusted the speed and feed rate to optimize cutting quality.
Testing Speeds and Feed Rates¶
In our group task, we conducted several tests to determine the optimal speed and feed rate for our CNC cuts. We experimented with different settings to see which combination provided the smoothest finish on our MDF sheet. The goal was to minimize rough edges and ensure precision in the final cuts. Through trial and error, we found that adjusting the spindle speed and feed rate had a significant impact on the quality of the cut. This testing phase was crucial in helping us fine-tune the machine settings for our individual projects.
Individual Assignment: Design and Fabrication¶
As previously mentioned, I turned to my mother for inspiration, and she had plenty of ideas. One idea that stood out was an open cabinet with shelves that could only be seen from one direction at a time, requiring you to walk around to see the other half. I drew inspiration from an image she found online and decided to give it my unique features along with press-fit joint cuts. Despite having experience in multiple CAD software programs like Fusion and SolidWorks, I chose to design the cabinet in SolidWorks due to my familiarity with it and my certification in it 😎.
In an effort to minimize material waste, I combined some of my mother’s ideas with random designs that popped into my mind during the final days of the week. I aimed to fit all these designs onto a single sheet of 2440 x 1220 x 12 mm (length x width x thickness) MDF wood. To ensure efficiency and accommodate the bolts securing the sheet to the CNC bed, I set an offset of at least 20 mm around the edges.
CNC Cutting Process¶
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Preparation:¶
- Clean the CNC machine and remove debris from the previous project.
- Secure the new MDF sheet with bolts at edges and middle spots, maintaining a 20 mm distance from corners to prevent bending.
- Minimize any natural bends in the sheet.
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VCarve PRO Setup:¶
- Export the design as a DXF file.
- Open it in VCarve PRO for detailed preparation.
- Add a 20 mm offset to account for edge bolts.
- Use the Dog-Bone fillet type for press-fit designs (radius based on drill bit size).
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Toolpaths Creation:¶
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Select the “2D Path” option in VCarve PRO.
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Starting and Cut Depths:¶
- Set starting depth to “0” and cut depth to “13 mm” (to account for 12 mm thick wood and sacrificial sheet).
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Machine Vectors:¶
- Choose “Outside/Right” to preserve specified dimensions during cutting.
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Speed and Feed Rate:¶
- Set spindle speed to 8000 rpm, feed rate to 80 inches/min, and plunge rate to 15 inches/min (using a 6 mm drill bit).
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ShopBot 3 Setup:¶
- Use ShopBot 3 software for precise CNC control.
- Align drill bit along x, y, and z axes.
- Pause and resume cutting as needed.
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Setting Up Drill Coordinates:¶
- Position drill near desired origin point (usually a corner).
- Set x and y coordinates to 0.
- Calibrate z-axis using metal plate and clip method.
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Z-Axis Calibration:¶
- Machine automatically touches metal plate to set z-axis.
- After calibration, carefully remove tools.
- Machine is now ready for operation. 🛠️🔩
Design Challenges and Errors:¶
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Offset Miscalculation:
- After days of consideration and planning, I finished the design on time, only to be told that it couldn’t be cut due to insufficient space left between the design and the edge of the sheet 😣. I had left only a 12mm offset for the screws to be inserted, whereas it should have been at least 20mm. If we had proceeded with cutting, the tool could have broke, ruining the entire design and potentially causing havoc in the lab 😬.
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Scaling Issue:
- Despite using parametric design on the joints to be 12mm exact, I tried the scaling command, thinking it would fix everything quickly without altering the parametric measurements of the joints. However, it did change them, leading me to the conclusion that parametric design might not have been helpful in this case—or perhaps I was negligent in some aspects that could have helped 🤔.
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Software Crashes:
- I faced repeated crashes in SolidWorks, which greatly affected my progress 😫. The crashes led to some designs being deleted and others changing due to unsaved dimensions. This caused me to waste a lot of time and repeatedly redo the designs. For example, after finishing the scaling, I was happy 😊, only to realize later that the design was on a dimensionless rectangular sheet that was above the limit of the wooden sheet 😩. This endless error broke me into pieces and left me unable to finish the cutting by the end of the week.
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Copying Dimensionless Designs:
- In an attempt to fix the issues caused by the crashes, I copied the design into a new part sketch without dimensions, thinking it would solve the problem. This was a mistake that I deeply regretted 😔, as it made things more complicated and led to more errors.
Despite these challenges, I eventually finished the design 🎉. I realized that the open cabinet could be re-integrated or reassembled into four more designs. Three were different ways the cabinet wall could be placed, making it wide open, while the other was for unique design enthusiasts like my mother. The fourth could be assembled into a partition, another one of my mother’s main ideas. This partition could also be reassembled in various ways, which I found extremely cool and fascinating 😎.
Design Cutting Challenges and Errors:¶
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Cutting Error Due to Wrong Toolpath Direction:
- I attempted to cut my design on another student’s MDF wooden sheet, as they generously allowed me to use the leftover space on their sheet. Initially, things went well—his design was successfully cut, and the machine began cutting mine. However, we quickly noticed that the coaster holders I had designed came out oddly shaped, weak, and flimsy. The result was far from the shape I had drawn in SolidWorks, but we initially brushed it off as a minor dimension error on my part. Unfortunately, this was just the beginning of a significant mistake. All of my designs on my classmate’s sheet were cut incorrectly because the CNC machine’s cutting tool was cutting inside the design lines instead of outside, leading to everything being wrong.
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SolidWorks Vector Issues:
- SolidWorks caused the vectors of my design to become zig-zagged, which made the cutting process noisy and inaccurate. The machine struggled to follow the intended path, resulting in a poor-quality cut. In hindsight, using Fusion 360 might have been a better choice, as it offers more robust vector handling and would have likely prevented this issue.
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Machine Stop Mishap:
- During the final attempt to cut my design, everything was progressing smoothly until a group of classmates needed to retrieve images from the CNC computer. They hurriedly accessed the file explorer to send the images via email, not realizing the machine was stuck on the Stop button, ready to pause the cutting process. As I stood behind them, cautioning them to wait until I finished, they accidentally paused the cutting. Though this was manageable, we panicked when we noticed the machine had stopped and quickly pressed resume without lifting the cutting tool or returning it to its origin point. This caused the tool to start spinning inside the wooden sheet, snapping and breaking it in half. We immediately hit the emergency stop button and called the instructor. He replaced the cutting tool and restarted the process, giving us a stern lecture on what we should and shouldn’t do in such situations.
Creative Additions:¶
Even after completing the cabinet design, I noticed that there was still a significant amount of space left on the sheet. This led to a burst of creativity, helping me regain some of my lost enthusiasm and dispel the growing frustration 🌟.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Tissue Cover with Space for Snacks:
- I decided to include a tissue cover surrounded by an empty space for water bottles, snacks, or mixed nuts for guests. It’s like a presentation plate for guests. This design was inspired by an image I found online.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Creative Coaster Holders:
- I designed a creative coaster holder with eight circular coasters. The holder is shaped like a mug with female joints, while the coasters have male joints that fit within it. This design was also inspired by an image online.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Wooden Board for Engraving Family Names:
- I created a wooden board in a unique shape, intending to engrave the names of my family members on it. My parents’ names would be on one side, while my siblings’ and mine would be on the other.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Stand for the Partition:
- I designed a simple stand for the partition to keep it from falling flat. The stand works by combining the shelves into the partition, with the other side of the shelf fitting into the stand. Although the stand is weak and a slight push could make it useless, I decided to include it on the sheet as it filled a spot. The partition can still stand if placed in a Z-shape, but this design is for situations where the user (my mother) wants to assemble them in one direction.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Glasses Stands:
- I designed three glasses stands. Two were uniquely done, designed as faces where the user can place their glasses as if they were wearing them 👓. The third is a smaller stand for three glasses, but due to limited space, it could only fit one, with the other two being used for keys or other small items. Unfortunately, the two uniquely designed faces could not fit on the sheet, so I plan to place them on another student’s sheet if they have enough space, of course if they accept.
In case you are interested in downloading the design’s DXF, STL, and SolidWorks file: Click here to download the DXF file, the STL file, and here for the SolidWorks file
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X-Shaped Cabinet Legs:
- As an alternative to the simple stand, I designed four half-circles with female joints to be placed in the middle of the open cabinet walls, creating X-shaped legs. This way, the cabinet can stand still without any worries. This too could not fit the sheet, so I also plan on requesting another student if it is fine for me to include it too in their sheet 😅.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
Creative Additions Changes:¶
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Design Changes for Efficiency - Book Stand:
- I decided to remove the stand for the partition and the X-shaped cabinet legs to save space on the sheet. The press-fit joints made it difficult to disassemble the parts, so a Z-shaped partition could be used instead if needed. In their place, I added a book stand, which could serve as a Quran stand—a perfect gift for my mother 😂. This stand consisted of two interlocking pieces forming an X.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Wooden Air Hockey Game:
- With some extra space on another student’s MDF sheet, I decided to create a small air hockey sliding puck game. The entire design was engraved to fit within the remaining space, and I set the depth to 0.6 mm off the 12 mm thickness. This quick addition was something I had wanted to finish despite being drained from the process.
In case you are interested in downloading the design’s DXF & SolidWorks file: Click here to download the DXF file and here for the SolidWorks file
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Coaster Holder Re-Cut:
- Finally, I used a small extra space on the sheet to copy and paste the coaster holders that had been cut incorrectly earlier. This allowed me to make better use of the material and ensure that nothing went to waste.