8. Computer controlled machining¶
Design¶
For this week I decided to make a chair.
Like all good things it was created in Fusion 360. I only used 3 parameters
-
Width
-
Length
-
Material Thickness
This helped me change the size of the chair to more closely mirror the scale of a chair in the real world. The material thickness parameter also controls the length of my tabs so I don’t need to change each one individually.
This is what it looks like without all the constraints:
This is what it looks like with some volume to it.
Making the Prototype¶
I sent this sketch over to the laser cutter to get an idea of what it would look like. I scaled everythign down so it wouldn’t take as much room.
I assebled it with masking tape and prayers 🙏:
This is a 100% truthful and not fake representation of how strong the chair is:
CNC¶
I then moved on to Aspire and set up the proper board dimensions I would be using to mill with.
I loaded my design into Aspire and scaled it to size adjusting the settings and adding tabs so the whole thign doesn’t explode:
I also added dogbones to my tabs so the bit could get the corners flush.
I also set the bit to be the 3/8” compression bitvwith multiple passes, ensuring that the surface finish on the cut edges of the board would not be splintery and ruin the finish/ require copious ammounts of post processing. The 3/8” compression bit combines up-cut and down-cut flutes to produce a clean finish on both the top and bottom surfaces of a laminated or veneered material, such as plywood. In some cases, multiple passes may be used to reduce the stress on the tool and machine. For example, a common strategy is to make the first pass just deep enough to engage the down-cut flutes of the compression bit, and then complete the cut in one or more subsequent passes. This can help improve material hold-down for smaller parts. Also for compression bits, ramping is critical for tool and workpiece longevity. A vertical plunge can compact wood fibers (swarf) at the bottom of the cut, which creates heat and damages the tool’s cutting edge and the workpiece. By ramping in, the bit enters the material more smoothly, allowing chips to be evacuated efficiently. I added tabs because they are a safety feature that prevents the finished part from becoming a loose projectile after it is cut free from the sheet of material. This is especially important for smaller pieces that may not be held down by a vacuum system once the surrounding material is removed.
Amalia and I milled out our designs together and worked together with the help of Elle Hahn and Angel Fang to learn how to use the CNC machine.
Amalia, Angel, and I went down to the shed to get wood, and as we selected our piece of wood, we used the thickness testers that were milled in the group assignments for this week.
We determined that 0.496 was the most accurate thickness for our wood.
First, we needed to open the Aspire file on the computer connected to the CNC machine.
Then, we needed to brad the wood down to the machine using plastic brads. Bradding the wood down to the machine keeps the wood from moving while cutting, which helps keep us safe. The brad nailer was empty when we needed to use it, so we had to load the brads.
Aircut:
After the air cut, we were confident that the ShopBot would mill in the right place.
Once finished, we vacumed the wood dust.
These are the finished pieces being taken out:
Assembly¶
The assembly was very simple I had all of my pieces and they fit together very nicely.
Here’s the assembled chair:
I realised when I assembled it I made a critical mistake, there was a last minute board thickness change. The problem with that was I had my materia thickness parameter set to a 3/4” board instead of a 1/2” board. That mean that my tabs would stick out by a 1/4”. Thankfully it still worked great and was only cosmetic. I still found the chair comfortable and suppoting when I sat on in.
I just took a saw and sawed off any excess, then the chair looked good.
Reflection¶
This week was by far my least favorite week. I had a ton of struggle getting the motivation to do it and I would be so happy if I never had to use a CNC machine again. I think they are great tools but I dislike the workflow for them.