8. Computer controlled machining¶
Assignment¶
Group assignment:
- Complete your lab’s safety training
- Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
- Document your work to the group work page and reflect on your individual page what you learned
Individual assignment:
- Make (design+mill+assemble) something big (~meter scale)
Hexagonal Stool: CAD¶
The design I chose to create this week was a hexagonal stool. The main inspiration for my design this week was Dan Stone’s CNC table. Although our designs don’t look similar on the surface, I based the legs of my stool on what he created.
I began by making a new file in Fusion and starting a sketch on the bottom plane. Here, the first thing I created was the hexagonal face of the stool. This part was very easy to create, as it only required a few things. First, I used the inscribed polygon tool to create a hexagon with a radius (center > midpoint of a side) of 10 inches. Then, I created a 3 in x 0.5 in rectangle 2 inches left from the center before using the circular pattern tool to pattern it another 3 times around the center. A picture of the result is shown below.
After creating the hexagonal top of my stool, I moved onto the creating the legs. As previously stated, I based the design of these legs on Dan Stone’s creation for this week. Because of this, I made two interlocking legs instead of four individual legs. These legs weren’t very difficult to design, so I won’t go too far into detail about how I made them. The general process I used was to start with the basic shape and dimensions (no fillets, no slot) before moving onto the details. Both legs are essentially the same except the slots in the middle of the leg are reversed (one has the slot on the top, one on the bottom). A picture is shown below.
After creating the sketch of my different components, I extruded all three (one hexagon, two legs) of them upwards by 0.5 inches to match the thickness of the plywood we have in our lab. Before I could actually connect them togethr to form a stool, however, I had to create dogbones on my slots. This is because the CNC machine cannot cut perfect 90 degree corners. In order to create dogbones in Fusion, I first followed the instructions in this video to install an add-on in Fusion for dogbones. Then, I went to my hexagonal extrude and selected each corner in the 4 rectangles before doing the same thing with the slots on the legs, creating dogbones with diameters of 0.25 inches in each corner. The picture below shows what the finished dogbones look like on the hexagonal top.
After creating the dogbones, I created a new sketch incorporating them. To do this, I simply started a new sketch on the bottom plane, chose “project” under the “create” dropdown tab, and chose all 3 components of my stool. After confirming this selection, a new sketch tracing the dogbones was immediately created. Although it overlapped with my original sketch, this didn’t matter too much because I can simply hide one or the other when I want to modify them. The picture below shows what this new sketch looks like.
Now that I had my dogbones and new sketch created, I could actually assemble the stool. To do this, I used the move and align tools under the “modify” tab to move each of the pieces until they fit nicely with each other. This process was relatively simple, and the picture below shows what my assembled stool looks like in Fusion.
Creating my CAM Toolpath in Aspire¶
To create my toolpath, I began by selecting the projected sketch I made (the one that has dogbones), right clicked on it, and selected “save as .dxf file”. Then, I emailed myself the dxf file and opened it on Aspire from a desktop. Throughout the process of creating this toolpath, I used Angelina Yang’s documentation for guidance. The first thing I did after opening the .dxf file was move my 3 parts closer to each other. This is because, without moving them, both the length and width of the file would be greater than 48 inches, which is the width of the plywood I will use to cut my design. I then measured the height of the plywood I would be using and found that it was 0.45 inches using calipers After this, I changed the file’s dimensions to the size of the plywood I would be using (48 inches by 96 inches across and 0.45 inches depth) before moving onto creating my profile cuts.
Feed Rate and Speed¶
According to a forum post on Vectric’s website (found here), “The feed rates are part of the tool you select from the database when you create the toolpath. You can change them in the tool database (you must then re-select the tool) or use the Edit button in the toolpath itself to change them just for that toolpath”. Because I didn’t change any specific settings in the tools that I selected for this job, the feed rates and speeds were left as default.
Profile Cut¶
The picture above shows the settings I used for my profile cut. The most important things to mention are stated below:
- Cut depth was changed to 0.45 inches
- Tool chosen was the 3/8 compression spiral
- Changed the number of passes to 4
- Length of each tab added was changed to 0.75 inches with a thickness of 0.125 inches
- I chose to add 6 tabs on the hexagonal cut and did the same for each of the legs
The rest of the settings were left the same as the default. The picture below shows what the profile cut toolpath looked like after changing these settings.
As you can see, the 4 rectangles in the middle of the hexagonal cut are not highlighted in pink. This is because I will be using a pocket cut for these.
Pocket Cut¶
The only parts of my design which I decided to do a pocket cut with were the 4 rectangular holes in the middle of my hexagonal cut. The image below shows the settings I chose for this pocket cut.
This pocket cut uses the same settings as my profile cut, with the only differences being that the pocket toolpath does not have any tabs and uses a 1/4 inch straight bit instead of the 3/8 spiral. The image below shows what both the profile and pocket toolpaths look like.
This was going to be the final version of my file before I sent it to the CNC machine, but I let my classmate Angelina Yang cut a part of her CNC design on the same file as mine; her documentation is linked above.
Cutting out my Design¶
After adding a few finishing touches to my file, I exported all of my toolpaths (profile and pocket) as a shopbot file for the CNC machine (I have attached both the Aspire file and Shopbot file at the bottom of my documentation for this week if you want to download them at some point).
Now that I had the file I needed, I put on eye/ear protection, went to the CNC machine (which had already been warmed up earlier that day), and followed this workflow made by Angelina Yang. I would recommend going to her documentation if you want to find a more detailed workflow than the one I have included below.
The first thing I did was bring in the plywood I would be cutting and nail it onto the table using a nail gun we had available in the lab. Once that was done, I loaded the shopbot file I made earlier and followed the following steps.
- Home the spindle
- Set the z-height to 1 inch above the material you are cutting. This is done in order to run an air cut.
- Run the file you loaded onto the shopbot. It won’t actually cut anything because of the previous step.
- Once the air cut is done, rehome the shopbot and get ready for the actual job.
The video below shows what the beginning of my air cut looked like.
Once these steps had been completed, I loaded the file I would be using again and reset the z-offset to be at the height of my plywood. I then proceeded to turn on the vacuum for the CNC machine before clicking “run” on the file. I was then prompted to hit the green start button when I was ready, and, after doing so, the cut began. The video below shows the beginning of the job.
How do you home/zero the spindle?¶
In the ShopBot application on desktop, there are a few shortcuts and options on the toolbar that you can use in order to home and zero the spindle on different axes. In order to home the spindle, all you have to do is type “C3” into the text box in the application, and the ShopBot will automatically home itself. Now, in order to zero out the x and y axes, you have to type “Z2” into the text box. This resets the x and y positions of the spindle to (0, 0), zeroing the x and y axes.
Problems Encountered¶
After my cut finished, I noticed that, for some reason, the dogbones I added to my design in Fusion were not there in the final product. Initially, I was very confused. I went back to check if they were on my Aspire file, and, sure enough, they were. However, after consulting with one of my lab’s instructors, Mr. Budzichowski, we realized that the dogbones I had in my file were too small for the bit I was using. The dogbones I created in Fusion had diameters of 1/4 inches, while the bit I was using had a diameter of 3/8 inches. I was quite worried about this at first, but the fix ended up being rather simple. After further consulting my instructor, we settled on the idea of just cutting the design again but with a smaller spindle this time. The same wood piece which I had just cut on would be used again. This meant that, for most of the job, the spindle would be cutting empty space. I was a bit worried about this at first, but this ended up working great! The images below shows what the final cut pieces looked like! I did mess up the hexagonal piece when recutting, which is why there are two hexagonal cutouts in one of the pictures. Other than this however, there weren’t any other issues when I was recutting.
Assembling the Stool¶
I took a few days to do other projects after CNCing my design, but I eventually returned to assemble my stool. Before I could do that, however, I had to first sand the pieces.
Questions and Issues¶
When I first tried to sand the edges of the hexagonal piece, I encountered some problems, mostly with the tabs on the cutout and the fact that some of my pocket cuts didn’t cut all the way through. To solve these issues, I consulted one of my instructors. Dr. Taylor. He told me that the best way to solve this issue was by using a multitool to remove the tabs one by one. He also told me that this same method would work with the unfinished pocket cuts. Sure enough, after trying this, the tabs came off cleanly. The pocket cuts were a little more troublesome because splinters would get stuck on the side, but that problem was solved as well after using the multitool for a few minutes.
Sanding¶
Now that all of my pieces were mostly free of any tabs/pocket cut issues, I moved onto using sandpaper to sand them. I first grabbed a P90 sheet of sandpaper and began sanding every side of my hexagonal piece. I then repeated this step for all of my two other pieces, the leg pieces, as well. This took about 5-10 minutes for each piece. Then, I used this same piece of sandpaper to sand in between each of my pocket cuts.
After using the P90 grit sandpaper, I grabbed an orbital sander with P120 and P200 grit sandpaper to finish sanding my pieces. I went over the same parts of my wooden pieces as I did with the P90 grit sandpaper, but after doing this twice, once with each piece of sandpaper, my design was much smoother. The picture below shows my sanded hexagonal piece.
I was now confident that my pieces would fit into their pocket cuts properly, and so I began to assemble my stool. To do this, I put my hexagonal piece on the ground and proceeded to insert both leg pieces into their respective pocket cuts. This worked successfully! The picture below shows my successfully assembled stool.
Group Assignment and Individual Contribution¶
Our group assignment for this week was to test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for our machine. The part of this assignment that I contributed to the most was testing runout, which I did by first taking a video of the spindle of the CNC machine spinning in the air (while not cutting anything). To test its runout, we attached a dial indicator to the spindle, which tells you the live runout as the spindle spins. From this video, we found that the average runout of our CNC machine’s spindle is ~0.0001”, or one-ten-thousandth of an inch. Because this is such a low amount of runout, you won’t really ever experience inaccuracies while cutting using this machine. The rest of our documentation can be found here.
Reflection¶
Overall, I felt good about this week. My lab as a whole experienced some difficulties as a result of our lab being closed over our spring break, but other than that, my cuts went relatively well and I only had to use the CNC machine once. The most important things that I learned this week were how to use the CNC machine effectively, how to create toolpaths using Vectric Aspire, and, of course, how to desing and CNC a design of my own. My files for this week can be found here.