7. Make something BIG¶
This week I learned how to use a CNC Shopbot milling machine to create something big.
Big is loosely defined as “meter-scale”.
I tried to make the most of the wood provided to us which was 1 x 910 x 1820 mm Softwood plywood (15mm thickness).
Assignments for this week (Mar 5 - Mar 11):
Group assignment:
- 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
Group Assignment:¶
I gained clarity into each steps of CNC Milling workflow, and understood the reasons for the many important precautions with using the Shopbot. These precautions are important as they can save ourselves from potentially life-threatening accidents, or preserve the expensive equipments and endmills from damage/wear-and-tear, or ensure good-quality end result.
See here for group documentation
My Learnings from testing the machine:
Our main learning in this assignment was of the importance of using a good endmill in ensuring clean cuts. Proper planning and inspection of equipments before starting on the machine can help us save time as well as unnecessary material costs.
We also learnt about the key considerations in designing for the Shopbot, such as;
- 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.
- We didn’t have time to test speeds and feeds, but when I have the chance it would be nice to play with different settings to see the difference
Individual Assignment:¶
I have a work-in-progress chair I made in Hida Takayama, which I like to use as a bag-holder / clothes hanger in my room. For a while I had an idea of extending this chair around the pillar, so that it could be placed in my entrance hall and function as a useful coat/bag-holder and stool.
I thought this week’s assignment is a good opportunity to experiment with this idea.
Design Plan¶
As I had limited time for this week’s assignment, I started with strategizing on how I could execute this week’s assignment as efficiently as possible.
Design Concept/Goals
- Create an attachment that expands the functionality of my stool
- Design in a way that compliments the original chair design
- Leave an open space below the seat to enable some more storage capabilities
- Make it press-fit, so it uses no screws or glue
- Make use of curvy lines to minimise corners
- Design parametrically to allow for adjustment on the day of cutting
- Most importantly, keep the design as simple as possible!
Inspiration
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.
CAD Design with Fusion360¶
1. Prototyping and Sketching
Once I knew the vague direction for my design, I sketched it out on my notepad with measurements.
2. Designing the parts on Fusion360
1. I started with drawing the top board, and adding in joints for the legs.
I tried to work parametrically so I can tweak the measurements on the day of the workshop based on testing results. I decided to offset my cuts by 0.3mm for the time being, which I later found out was not needed.
2. After measuring the dimensions between each joints, I drew out the legs. Then, I extruded the sketches by the material width of 15mm.
3. I made sure to account for the milling bit diameter by making corners into 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 decided to use rounded corners 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.
4. To make the Bottom board, I duplicated the Top board and xxx.
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 completed, we are ready to move onto assembly.
3. Assembly
1. I inserted all the parts onto a new file, and assembled them (below picture is lacking the 2nd leg).
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.
2. 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.
This iteration part of designing was where I really felt the value of CAD Design; I was actually enjoying the process of experimenting with different designs with just a few mouse-clicks!
Although my tree design was still rough around the edges, I decided to stop myself before I got carried away. I could spend many more hours refining the design, but creating a perfect design was not the main goal of this week’s assignment.
So I inspected the joints carefully for good fits, then moved onto arranging them onto a sheet for 2D conversion.
4. Arrangement and Export
1. Before arranging the parts, I turned each designs into components. (Although I don’t know the exact reason we do this, few people have recommended it.) I then made a rectangular object the size of my material, and lay the parts onto it. I didn’t try the automatic layout this time, something I hope to try next time!
2. 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 (yes, this defeats the purpose of parametric design…).
3. 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 CAM Toolpath production.
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 is strongly recommended to use VCarve as the default CAM software. - Shopbot
These are the steps I took to generate the Toolpath:
1. Import the .DXF file
2. Set up parameters for cutting
→ Material dimensions
→ Tool (mill) information
→ Feeds and speeds, depth of cut
3. Add Tabs for support
4. Generate the CAM Toolpath, and check that it looks ok.
5. 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.
CNC Milling¶
We used this Shopbot Standard at FabLab Minatomirai.
As we had some left over material from groupwork, I decided to do a little test-cut to test the joints first (thanks to suggestion from my instructor Nagano san).
The test joints came out perfectly good, 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. Set up machine
- Fix material onto the bed (sacrificial layer) of CNC with screws 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, turn on Exhaust
2. Start milling
- Follow the safety procedures and always be prepared to stop the machine in case of emergency
- While milling, check the wooden chips and the noise. If necessary, change parameters such as feed rate, spindle speed, etc.
Post-milling¶
Once milling is completed, vacuum clean the chips, unscrew, cut the “tabs”, and sand down rough edges and corners.
Finally, before leaving, make sure to clean the CNC and room for the next person using it.
Final Result¶
Reflections:¶
Given the little time I had this week, I’m happy with the end result! Although if I were to improve one thing, I would use thicker wood for the leg, or use more than the 2 layers I used. I also would have liked to make some pockets, which I had to give up due to troubles 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 :(
Some of my learnings:
- Parametric design is a good idea in theory, but setting it appropriately is not always straightforward
- The tolerance is not a must for Shopbot especially with a good quality endmill, and since we will sand-down at the end anyway.
- Design iteration on Fusion360 is fun and can make a big difference in end result, but you could easily spend days just iterating. Remember to keep time-management in mind.
- Adopting Curvy lines is a good idea for Shopbot, as it can minimise details which are the key reasons for longer cutting times. My design only took around 15 minutes to cut.
- This week was a busy week personally (for my day time job) and 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.
Design files:¶
Useful links:¶
- CNC Tips
- Useful documentation 1
- Useful documentation 2, quite comprehensive
- Useful documentation 3
- Living hinge
- V-Carve tutorial
Assignment Checklist:¶
- [ x ] Linked to the group assignment page
- [ x ] Documented how I designed my object (something big)
- [ x ] Documented how I made my CAM-toolpath
- [ x ] Documented how I made something BIG (setting up the machine, using fixings, testing joints, adjusting feeds and speeds, depth of cut etc.)
- [ x ] Described problems and how I fixed them
- [ x ] Included my design files and ‘hero shot’ of my final product