7. Make something BIG¶
This week I learned how to create something big using a CNC Shopbot machine.
👉CNC (Computer Numerical Control) Machines are computer-controlled machines used in manufacturing to precisely cut, drill, or shape materials like metal, wood, and plastic. The process involves a computer programmed with software that generates instructions, or G-code, to guide the machine’s movements along the XYZ axes, achieving high accuracy, speed, and repeatability in producing complex parts, with minimal human intervention. Google AI summary
Group assignments:
- Complete lab's safety training
- Test the lab's CNC machine (runout, alignment, fixturing, speeds, feeds, materials and toolpaths)
Individual assignment:
- Make (design+mill+assemble) something big. (Big is loosely defined as "meter-scale")
Group Assignment:¶
After FabLab Minatomirai gave us a very thorough training on their SHOPBOT PRS Standard 96-48, we attempted to test the machine (which unfortunately had to be cut short due to bad endmill quality).
See here for group documentation
My Learnings:
The large size and power of CNC machines comes with it many hazards such as Mechanical hazards, Electrical Hazards, Flying debris, etc. So the safety precautions are very important in helping us avoid potentially life-threatening accidents, eye damage, ear damage, etc.
In addition, the machines are also very expensive to install and maintain, and the precautions help us preserve these expensive machines and tools (such as endmills) from unnecessary breakage and wear-and-tear.
The safety rules at FabLab Minatomirai can be found in the above documentation.
Importance of Inspection before using machine:
- The groupwork taught us that without proper inspection of the equipments before starting on the machine, we can lose a lot of time as well as waste unnecessary material. This includes inspection of the endmill, which we learnt is a fundamental requirement of producing decent results. In terms of the inspection of the machine itself, Rico did some of them before the groupwork, which included looking at the stability of the arm, the slant of bed, etc.
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As we lost a lot of time on the first day due to using a bad endmill, we had to stay up until late to finish our 3D model as we only had 8 remaining hours between 3 of us to use the Shopbot. Although we were all careful to make sure no accidents occured, I really felt that it was not ideal to use the machine when anxious/tired.
Other key considerations when designing for the Shopbot; -
CNC cannot cut 90° corners - there will always be a trace equal to the end diameter. So we need to fillet or dogbone corners according to milling bit diameter.
- Accounting for kerf is not necessary unlike laser cutting, as CAM softwares have features to cut outside the line.
- Offsetting for fit clearance is not always necessary, especially with a good quality endmill, and as there will be some sanding down of surfaces in the end anyway.
- Simulating the cutting pass, such as Toolpath preview and Airpass before the actual cutting can be a good idea, to check for unexpected paths.
- Because of the endmill issue, we ran out of time before testing speeds and feeds (which is supposed to be a key learning outcome of this week). Fortunately, the figures recommended by the manufacturer worked well, but I would like to try experiment with different settings when I have the chance in the future.
Make Something BIG:¶
I have a work-in-progress chair I made in Hida Takayama, which often ends up acting as a bag-holder / clothes hanger in my room. I wanted to prototype an extension for this chair, giving it more useful features to make it fit to be placed in my entrance hall.
1. My Design Plan¶
I started by thinking about how to prototype the extention in the limited time I have this week.
Design Constraints:
- Goal is to prototype another chair/bag-holder that extends my existing stool.
- The design should complement the current stool in some way.
- I would like to leave an open space below the seat for storage.
- It should be press-fit, using no screws or glue, so it could be dismantled easily.
- Make use of curvy lines to minimise sharp turns (which CNC takes long time to cut).
- Design parametrically to allow for adjustments on the day of cutting.
- Make as much use of the material provided to us (one 910 x 1820 mm Softwood plywood, 15mm thickness)
- Most importantly, keep the design as simple as possible!
Initial Research for Ispiration
I went on Pinterest and searched “Press-fit furniture”, “CNC furniture” to get some design ideas.
I especially liked the way the chair on top left creates a space underneath without compromising stability and design.
2. CAD Modelling on Fusion360¶
2.1 Prototyping and Sketching
Once I knew the vague direction for my design, I sketched it out on my notepad with measurements. (Unfortunately I discarded the sketch before taking a picture.)
2.2 Modelling each components
- I started with the top board, drawing the oval shape, and then cutting out joints for the legs. I decided to offset my cuts by 0.3mm for the time being, to account for the kerf, but I later found out was not needed with CNCs.
- After measuring the dimensions between each joints, I drew out the legs. Then, I extruded the sketches by the material width of 15mm.
- I made sure to account for the milling bit diameter by turning all the corners into either curves and dog-bones.
I preferred the look of rounded corners over dog bones, and since I enjoy using manual tools to sand-down corners, I tried to use rounded corners as much as possible, especially where they will be visible.
I found out later that there was a more ideal way to draw dog bones, which is useful to know next time.
- To make the Bottom board, I duplicated the Top board and cut out the center to make it more lightweight without compromising stability.
At this point, I showed it to my instructors, who gave me some useful advice, such as avoiding sharp angles narrow cuts.
I also made a small pocketed part, just to learn how it is done.
Once all the parts are designed, we are ready to move onto assembly.
2.3 Assembling components on CAD
- I inserted all the parts onto a new file, and assembled them (below picture is lacking the 2nd leg).
After seeing the assembled chair, I decided I didn’t like the straight legs, so I made them curve a little to complement the legs on my original chair. - In this process, I realized that I want to make the designs a little more curvy, something that would be harder to achieve with manual woodworking. Then I had an idea to make a tree-like design to complement my original coat-hanger stick.
I found the process of iterating the designs on Fusion quite enjoyable and empowering, but I decided to stop myself before I got carried away. Although my tree design was still rough around the edges, refining the design would be an endless process, and the goal of this assignment was not to create the perfect design.
I inspected the joints carefully, then moved onto arranging them onto a plank of wood in order to convert them into 2D images.
2.4 Arrangement and Export
- Before arranging the parts, I turned each designs into components. (Although I didn’t really understand the exact reason for this.) I then made a rectangular object the size of my material, and laid the parts onto it. Automatic layout feature would have been easier and helped minimise waste, but I could not find this feature, so I hope to try it next time.
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By this time, we had finished the Group assignment and I had to cancel the offset value I set of 0.3mm. I struggled with adjusting the parameters without messing up the design, so I found it much faster to adjust them manually😢
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Once happy with the arrangement, I projected the face of each parts to make a 2D vector sketch, which was exported as a .DXF file. With this file, we are ready to move onto generating a CAM Toolpath.
3. Generating a CAM Toolpath¶
👉Toolpath is defined as the instructions, or series of coordinates, that define the path a cutting tool will follow to machine a workpiece, essentially dictating how the tool moves to create the desired shape. At FabLab Minatomirai, it was strongly recommended to use VCarve as the default CAM software. - Shopbot
These are the steps for generating the Toolpath:
1. Import the .DXF file
2. Set up parameters for cutting
| Parameter | Description | My settings |
|---|---|---|
| Material dimensions | The size of our material | 910 x 1820 mm |
| Tool (endmill) information | 1/4 inch Solid Carbide router, 2 flute, Downcut extreme heavy duty | |
| Feeds | Amount of engraving per cut. The goal is to achieve balance between speed and quality | 3 inches/sec |
| Spindle speed | Endmill’s rotation speed. Too fast can burn the material, too slow causes rough finish. | 12,000 r.p.m. |
| Pass Depth (Depth of cut) | Slower is safer. Usually equal to or less than tool diameter to prevent stress on tools. | 1 inch/sec |
- Add Tabs for support
- Generate the CAM Toolpath, and check that it looks ok.
- Export the gcode file
When I tried to generate the toolpath, I ran into an error about open vectors. This was strange because there was no open vectors on Fusion.
4. CNC Milling¶
This is the Shopbot Standard we used.
As we had some left over material from groupwork, I followed Nagano-san’s great suggestion to do a little test-cut of the joints.
The test cuts produced great results, so I moved onto cutting all the parts.
Below is a brief rundown of the CNC milling workflow. You can check the detailed steps on the Group Documentation that I wrote.
1. Prepare and Set up machine
- Fix material securely onto the bed, or sacrificial layer, of CNC, making sure the screws are placed outside of toolpath.
- Set the XY origin.
- Do an airpass first, by setting the Z origin at around 150mm above the surface.
- Once ready, set the Z origin, and turn on the Exhaust.
2. Start milling
- Follow the safety procedures and always be prepared to stop the machine in case of emergency.
- While milling, check the quality of wooden chips and the noise. If necessary, change parameters such as feed rate, spindle speed, etc.
5. Post-milling¶
They came out great with no uncut areas. Once the machine is off, vacuum clean the chips, unscrew, cut off the “tabs”, and sand down rough edges and corners.
Maki san helped me unscrew the material
Finally, before leaving, make sure to clean the CNC and room for the next person using it.
6. Final Result¶
Reflections:¶
This week was a particularly busy week for my day time job and I must say it was not ideal to operate Shopbot while sleep-deprived and quite stressed. But thankfully I made it work with support from my instructors and classmates.
Given the limited time, I’m quite happy with the end result. If I could improve one thing, I would use thicker wood for the leg, or double the layers, to increase stability. I also would have liked to make some pockets, which I had to give up due to difficulties with open vectors.
All in all, I found this week’s assignment very enjoyable, and it’s empowering to know that I can produce my own furniture relatively quickly. However, considering the lumber cost (which I was told is around 35 USD, for a mid-quality plywood!), it’s impossible to compete with mass-produced IKEA furniture!
More Learnings about 3D-CAD modelling.
- I know parametric design is a really good idea in theory, but I still struggle with setting it appropriately. I couldn’t adjust my offset values without messing up the whole design, so this time I had to resort to adjusting manually.
- Design iteration on Fusion360 was fun and it was satisfying to see the designs change with few clicks of the mouse. But I also learnt the importance of keeping time-management in mind, as you could easily spend days fine-tuning the design.
- When modelling for the Shopbot, I learnt that small details and corners are where the machine takes the most time to cut. Because I adopted a very curvy design, it only took around 15 minutes to cut, which was significantly faster than my peers.
Design files:¶
Useful links:¶
- CNC Tips
- Useful documentation 1
- Useful documentation 2, quite comprehensive
- Useful documentation 3
- Living hinge
- V-Carve tutorial
Assignment Checklist:¶
- Linked to the group assignment page
- Documented how I designed my object (something big)
- Documented how I made my CAM-toolpath
- Documented how I made something BIG (setting up the machine, using fixings, testing joints, adjusting feeds and speeds, depth of cut etc.)
- Described problems and how I fixed them
- Included my design files and ‘hero shot’ of my final product