For this project, I worked alone to produce two CNC nouns. My original plan was to go for a mountain cut, but I was heavily constrained by time, so I settled on a noun. I have had some CNC experience in the past, both from high school and from ENGI 120/FWIS 188, but it had been some time since using the machines.
PHASE 1: Noun choosing
During training, I attempted to use a car for the noun, but the shape was too complex for the CNC to cut out properly. So to keep the vehicle theme going, I found a good steering wheel design that was reminiscent of 50s-60s racing wheels which I thought was neat. Overall, it would be an easier noun to cut on the CNC machine.
PHASE 2: Setting things up in carbide create
The next step was to set-up the job for the CNC machine in Carbide Create. For this project, I had to use the Shapeoko XXL as the Nomad 3 was heavily booked. In the software, I made some edits to the file as only circles of certain size could be cut with the 1/8″ end mill. Then, I added the tool paths for the cut.
Design edit to add pocketable holes
For this first cut, I pocketed the circles and countered the other shapes to leave only the shape of the steering wheel. This contour was split into two parts, the inner- and outer- contour. Eventually, a set-up with two parts and pockets first was made for a larger piece of stock to cut.
Planned tool paths
In the simulation
PHASE 3: Issues with first cut
There were some noticeable issues with the first cut. Even when using tape and clamps on the bed, the piece got dislodged due to the movement of the leftover stock after the first contour. The job had to be stopped because it was incorrectly cutting one of the pieces.
Incorrectly-cut pieces
With this issue identified, I had to prepare a new tool path where the inner contour was changed to a pocket. This would reduce total contour commands to only one contour to remove the piece.
PHASE 4: Trying again with new paths
As a general comment, the probing feature was a bit unreliable when homing the piece. Despite being in the correct corner for the homing, the machine would not move over the probing piece to home the z-coordinate correctly. Furthermore, the proper homing piece for the Shapeoko XXL was not usable due to the size of the mill housing opening. To work around these issues, manual homing at the corner of the stock was used.
For the new path, the inner contour was changed to pocket, which would reduce any risk of leaving loose stock during the job, and also to simplify the cutting process for the part. With that, the job was ran, and successful it was.
New paths
Cutting with the new g-code
Successful pieces!
PHASE 5: Post-process and completion
To post-process the part, the plan was to sand the cut pieces and then paint the piece with a color scheme to match a steering wheel.
For sanding, the parts were sanded with 100 grit up to 220 grit to remove excess scrap from and to smooth out the piece.
Sanded piece
For painting, it was settled to hand-paint the piece as it would be more precise to paint the sections of the piece. To hand-paint, spray paint was applied to a sponge, and then a small-tip brush was used. The inner pockets were painted black to simulate a black background, the center was painted silver, and the outer rim and body were stained with American Chestnut. These colors simulated the wood-trimmed wheels of racing cars from the 50s-60s, and overall the colors turned out pretty neat.
Painting the pockets
Center painted silver
Completed pieces!
PHASE 6: REFLECTION AND COST ESTIMATE
Despite the initial issues with operating the CNC machine, I felt that the project was completely successfully after iterating on things such as path design. If I were to improve on things, I would look to open to dedicate more time to the iteration of the cuts as it takes a while to set-up and have the machine running. Overall though, CNC machining proved once again a neat process to create clean parts.
The following is an estimated cost of the nouns:
- Material: Wood (full plank by Home Depot) = $3.00 estimate
- Material: Paint = Negligible
- Labor: $19.74/hr (national average for a spray painter by Payscale) x 1 hours = $19.74
- Labor: $23.32/hr (national average for CNC machinist by BLS) x 4 hours = $93.28
- Overhead Cost: $35/hr (for a 3-axis CNC Machine by RapidDirect) x 4 hours = $140
The estimated cost for the noun pieces is $256.02. To reduce this cost, a lot of labor and machining time with the CNC must be reduced as heavy costs were imposed on the final product due to the iteration and trial time on the CNC machine.
