7. Computer Controlled Machining¶
Files¶
Overview¶
This week I deisigned a table in fuison and cut it on the ShopBot. To do this I sent the fusion file over to aspire where I turned the CAD file into a CAM file (Computer Aided Machining).
Group Work¶
Our team worked on various aspects of CNC machining, including runoff testing, thickness gauge design, and documentation. Before using the ShopBot, we completed safety training with our instructor, David Taylor, and followed a structured workflow for operation. Our lab contains both large and small milling machines, allowing us to cut materials like wood, plastics, and metals, each requiring specific settings for speed, feed rate, and dust collection. We also experimented with different fixturing methods, using jigs for smaller projects and plastic brads for securing large sheets.
For runoff testing, I worked with others to measure the accuracy of our cutting depths. We used a runoff tester to determine how much extra depth was needed when cutting, as measurements alone weren’t always precise. We tested multiple bits—such as a 3/8” bit on the large ShopBot and a 1/4” bit on the smaller one—finding a consistent variance of 5 thousandths of an inch. This small adjustment helped us refine our cuts, ensuring better precision when milling our final designs.
Runoff¶
To test runoff we used a runoff tester on several bits to find out how much more depth was needed when cutting a board since mesuring to board isnt enough sometimes since the tools are never exact. To figure out how much room was needed we tested the spin of three diffrent bits while mesuring them with the runoff tester. We tested the 3/8ths on the big shop bot and the 1/4th on the small one. In both tests we found that the meter moved to 5 thousandths of an inch. This was later applied when cutting out our designs since we knew that their was a small margin that needed to be added.
Fusion¶
What to make¶
Going into this week I was unsure of what to make. A shelf or a stool sounded to generic and I didnt beleive I’d use them in my home at all. The idea for a table stuck out to me since it felt practical and it just sounded fun to me.
Designing the Table¶
To start I first mapped out the area I had to fill with the help of contruction lines making it 48 by 48 inches since that was half of the space on the shopbot. After that I first made the table face as big as I could while keeping the length to width ratio close to what I wanted it to be (1.5 to 1). Once that was in I started working on the legs. I liked the idea of triangle legs since it still put the weight at one point but at the same time could hold up a large area and look plesant. Once that was all done I made some parametric values for the tabs so that all the parts worked together in press fit. Once that was all done heres what it looked like:
Failed ideas and Testing Model¶
At one point I thought about making the inside part of the leg have a tab in it and make a stool to go along with my table. I scraped this idea though since when I made a test of my model the legs came out to be to low since I didnt account for how a table works so I had to remove the stool to add room for the legs to grow. The test I mention is me cutting and printing out a model of the design that was scaled down.
Heres it printed
Heres what a 1:1 scale of it in carboard looked like.
Aspire¶
Setup¶
First thing I had to do was give the dimensions of the board. To start i made it 48 by 48 but changed it to 96x48 later since it was the size of the piece of wood on the shopbot. Along with that i made my board thickness 0.5 inches and went from bed surface.
Dogbones¶
After the dimensions were set and my file was added, I had to add dogbones to my tabs since the drill bits are unable to make the 90 degree cuts so the tabs needed to have rounded corners as to not break the bit. The dogbone tool has multiple options for what they can look like. I used dogbone and tbone. Dogbones were used on the edges of the tabs and the tbones on the inserts on face of the table.
Heres all the diffrent types of dogbones
Here are examples of both types of dogbones I used in action.
ToolPaths¶
Preview¶
Tabs¶
The wood when cut needs something to hold it to the rest of the board so that it doesnt fly out. Thats when tabs are added to parts around the wood which can be cut out easily. I was paranoid and added far to many tabs to my design which came back to hurt me when I cut it out, but none of my pieces went flying though.
Shopbot¶
To learn how to use the ShopBot I followed this Workflow
Setup¶
The first thing I had to do was remove the piece of wood that was on the bed of the shop bot since it had been completly used. To do this I used the crowbar on diffrent areas that had been cutout to push out the brads holding the board to the bed. After I did that I got a new piece of wood and placed it on the bed.
Brads¶
As previous mentioned, brads are used to nail the piece of wood down to the bed of the shopbot. Brads are just nails that have no head. This is acomplished with the help of the nail gun. It uses pressurised air to shot the brads through the board and into the bed. The pressurized air is created using a air tank and after I used it I had to open the valve on the bottom so that their wouldnt be a tank of pressurized air sitting on the floor since its very dangerous. One thing to note is that the brads need to be longer then the boards width is since if they are not, then it wont hold the board down well.
Aircut¶
The first thing I had to do was run an aircut of my files so that I knew that they toolpath was cutting the right area. To do this I jogged the z axis up 2 inches and then set it at the zero
Cutting out¶
Assembely¶
Sanding and Removing Tabs¶
Since I added some many tabs to my board it took a long time to remove all the tabs. Afterwards I sanded down the
A sad relization¶
After getting the pieces off the bed of the shopbot and getting the pieces sanded down the problem emerged. I had set the cut of my tabs as an outside cut, this caused thier to be an extra 0.5 inches of area in the tabs since the quarter inch bit went
Solution¶
To get the dessiered close fit I printed a part to go along side the tab that accounted for the area where theier wasnt tab. After I saw that it could stand up, I used superglue to make it secure.
Reflection¶
This week was really fun for me since I got to come up with an for a table in my head and eventually put it together which I think is just amazing and truly shows what fabrication can do. I had sturggles and faults with the ouside cut on the tabs but found a way through them. I think one of the most fun weeks yet since I always have liked the more hands on aspect of engineering.