Computer-Controlled Machining¶
Goals¶
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
Prior Knowledge¶
I’ve never used the ShopBot. I will be using CAD and laser-cutting for prototyping, however, this will be quite new to me.
Projected Timeline¶
- Wednesday
- Refine design
- Thursday
- Finish design
- Friday
- Mill
- Saturday
- Documentation
- Sunday
- Documentation
- Monday
- Assembly
- Tuesday
- Get ahead
Actual Timeline¶
- Wednesday
- Refine design
- Thursday
- Refine design
- Friday
- Finish design
- Saturday
- Document
-
Sunday
- Laser cut prototype
-
May 21
- Mill
Group Assignment¶
I was in a group with all the other girls.
You can see our documentation on our group site. I was assigned materials.
Individual Assignment¶
Fusion¶
I already have a design, however, I learned that dowels are not the required press-fit. I changed to the box joint type, and in doing so, needed to create sides as opposed to simply pressing two pieces of wood together. Considering that the wood is 3/4 of an inch, I did not think this part through. I should add that 1/2 inch is also an option, and while 3/4 is used for furniture that one sits on and routinely uses, one would likely stand on the course to improve their angle.
Sides¶
I clicked the letter I to measure the length of the six sides. I then made rectangles with those lengths and a height of 6 inches. I figured that this height would be adequate for the contents of the structure. Still, one can play and stand on a course of this height without issue.
Tabs¶
I created rectangular patterns for each tab, each .75 inches in height and 1 inch in width. At first, I tweaked variables to match the distance and quantitity with my desired tab length and path length. I refer to the line that the tabs are on as the path. I eventually streamlined this process into selecting the tab and a line of equal length next to it and setting the type of extent to spacing. I click the direction, set the distance to the tab length, and set the quantity to the path length divided by the tab length. This may sound tedious, and was for the first few. I adapted to the process.
While fixing this design, I asked Dr. Taylor practical questions. Mainly, I was curious about tab dimensions, and he explained that the main risk is the tabs not aligning properly. If I am cutting half an inch, for example, the tab height should be half an inch. The length is less significant. I was also wondering about my lake and bunkers. While milling the circles was no issue, I cannot fill the entire strucure with water to make a lake, or with sand to make bunkers. I needed some sort of container and was unsure how or if I could go about it. Dr. Taylor mentioned that I should make one for molding and casting week. I decided that I would assemble the bottom piece and sides, but place the molded containers in before adding the top.
It occured to me that, since precision is - as I mentioned - extremely important, I needed to try this design before committing. I would do so with a machine I was already familiar with: the laser cutter! I would of course scale the design down and likely use thinner wood. Not cardboard, as I did need a definite answer as to wheter the tabs can fit using unmovable material.
I created and mirrored the tabs for the top and bottom as well as the sides. The top and bottom have identical tab dimensions while the sides have the opposite tab layout.
I considered making the tabs slightly shorter for a greater chance of fitting the sockets. I might still for the laser cutter, but for the ShopBot, I can always cut the tabs on the line and the sockets inside, or a similar combination that uses kerf for the fit.
Laser Cutting¶
I exported the file and performed a laser cut. I learned very quickly that while scaling 1/3 is one thing, scaling to the point that the tabs are barely visible is - entirely - another.
When I originally used plywood, Mr. Dubick informed me that cardboard is faster and less costly. I stopped the job and replaced it with cardboard.
I found that the tabs did fit, and Ms. Dhiman confirmed that I should set the tabs to the exact same length as opposed to one being slightly smaller than the other. She also advised me to mill pockets, which are my lake and bunker spots, inside the line. The tabs were actually too loose, although I chalked this up to the kerf taking up around half of the tab.
It went well otherwise, though.
Putting Out Large Fire¶
We backed away from the laser cutter and Mr. Dubick talked us through putting these out.
- Stop fire
- E-stop
- Turn fans off
- Extinguish
- Find plywood block
- Open laser cutter
- Quickly place block over fire
- Close laser cutter
- Wait 1-2 minutes
- Re-open and take plywood out
- Clean
- Take material out
- Brush ashes into the grooves
Milling¶
Since there were no errors outside of scaling, the tabs technically fit. The looseness was related to the kerf, not the dimensions, as the Fusion 360 file has uniform tab and socket lengths which transferred.
Instead of risking another fire and needlessly retesting, I would use, well, a considerably more dangerous machine with absolutely no experience.
Aspire¶
One of my main weaknesses in Fusion is that I cannot properly align objects on the z-axis. Although from home view, they look proper, they seem distorted when I import them. Still, each part scaled consistently. I now had to perform several transformations in order to fix my original file.
After moving these around to save space, I used Interactive Trim on the tabs. I consider this function the Aspire equivalent of CorelDraw’s Virtual Segment Delete.
I asked Mr. Dubick about the tee box and the green, that is, the two circles I intend to attach to the top of the course. I was unsure if I would need some sort of dowel attachment. He informed me that I could just glue it. Also, while he said that I could technically cut it at this point since we’re short on time, I did not need nearly as many tabs as I had.
He later checked the time it would take to cut each piece and found out that I could not, in fact, mill. A design over three hours per piece just seems time-consuming for no practical purpose. Unfortunately, although I would have to mill after spring break, I needed to directly modify the Fusion 360 file. Back to the drawing board.
Fusion 360¶
I started out by deleting all of the tabs and repeated the process with 5-inch tabs instead. Since there was nothing new in the process, I just screenshotted the result.
I did find a more efficient way to mirror the tabs. - Start by splitting the body. Skip this if you extruded the tabs using the “new body” operation. The tabs should be separate from the main shape. - Construct a midplane on the shape. The sides would be the tool you used to split the body and the opposite side. - Mirror each tab across the midplane. - Delete the midplane, unless you plan to modify the tabs and use it again. This is optional. - Combine the body once finalized. Otherwise you will need to do so in your cutting sofware, which tends to take longer.
In the original, the longest side had thirty-three tabs. Currently, that side has seven, making this a far more reasonable cut. After mirroring the tabs and combining each body to hopefully avoid trimming, I just need to wait until after break. Once I’m back at the lab, I can access Aspire and send the file over.
Test Cut¶
I laser-cut with the spaced-out tabs. I found an error in the thickness and tab count of one piece, which I fixed and re-cut. There were no other errors.
Aspire¶
I now needed to import the file and scale properly, since the dimensions far exceeded that of the plywood. Mr. Dubick brought it to my attention that the maximum dimensions are 48*96.
CNC Milling¶
Dr. Nelson helped Zaina and I through milling, and Mr. Dubick with assembly. Thank you!
We placed the board onto the bed, aligning the material with the sides. We used plastic composite brads to secure the board.
Toolpaths¶
I created three toolpaths, respectively: circles, sides, and main. Order matters, as cutting from the inside out is optimal due to the least possibility of movement. These toolpaths were all profile toolpaths, which indicates that the machine cuts straight through.
Thickness¶
The wood measures 1/4 inches in thickness, which we confirmed with calipers. We used .251 as our thickness, adding the thousandth is optional. The amount of passes adjusts to this measurement, mine needed one.
Tabs¶
I needed to manually create dogbone tabs in each inner corner for ease of tool movement. Then, I automatically created tabs 12 inches apart for the main and sides, 8 inches apart for the circles. The smaller the distance, the greater the number and vice versa.
Bits¶
The largest tool works most efficiently, with the exception of small details. My tabs required a 1/8 straight end, as opposed to the 3/8 downcut I would have used had they been wider.
Once finished, I checked over every aspect of the toolpaths.
CAM Settings¶
- Circles
- Main
- Sides
Milling¶
We sent the G-code to the CAM software, jogged the x-axis, and began the cut. The machine continued for 10-15 minutes. Afterwards, I confirmed that every part was cut.
I then climbed onto the machine, with permission, and sawed away the tabs to take each piece out. This was the most enjoyable part.
Assembly¶
From here, I needed to confirm the fit of each piece. Fortunately, there were no errors in tab count.
I did not, however, account for the sides overlapping in the design. I used a tablesaw, and with help, repaired a piece I cut too short with a sawed piece.
I taped the sides to keep them from falling.
I needed to use glue and a nail gun to secure each piece.
Now that the sides were secured to the bottom, I could add the top.
The nail gun did not work after setup - it would only release air despite the nails being properly loaded and the gauge working. Mr. Budzicowski solved the problem. Afterwards, I sanded faulty areas and. nailed the top.
Reflection¶
Group Work¶
I learned a bit about the materials we use. There was nothing particularly difficult.
Positives¶
The assembly was extremely rewarding. I saw the lines from Fusion 360, and every deliberate change I made, transform. With a combination of prototyping, time, and some luck, the design worked on the first try!
Negatives¶
The Fusion 360 files are not especially versatile - I can edit seamlessly on that platform, however, some files render incorrectly in Aspire. Closing the vectors and creating dogbone tabs are simple yet tedious. Of course, this is coming from someone who initially added 20 tabs to a single side. The process usually takes under ten minutes.
Takeaways¶
Learning how CAD transfers on a meter scale fascinated me, as I have never used a CNC mill.