Class Work
3-Axis CNC Mill
The Epic 2.72 Mill
2.72 holds a certain special place in the heart of anyone who’s ever taken the course. Stockholm Syndrome, some would call it, but I prefer “Survivor’s Glory”. The course centers around the design and build of a precision desktop lathe using parts and a budget provided for in the class. Marty walks you through a lot of design steps and labs, and every two to three weeks your team meets with him personally in design reviews.
These events are always exciting. I remember that for the first design review we got an email two days before saying “none of you have been in contact with me about what exactly I want to see in the first design review. Interesting, given that I’m your boss here and I expect certain elements to be complete. Further, I refuse to accept incomplete presentations, and will require you to push back a day. Each day you push back removes 75 points from the 100 possible design review points, and do note that negative scores are possible.”
No one had completed what was necessary to present the first day.
We came in on the second day and showed off our work, which Marty was quite pleased with, but regardless we walked out with 15/100. We all hoped these were “who’s line is it anyways” points.
Our team significantly differed from the standard 2.72 team in that instead of designing a lathe as was typical for the course we opted for the alternative design goal of making a 3-Axis Milling Machine. The specifications weren’t clear, and we were forced to execute a very open design loop in order to decide on what our final capabilities could be, and from there work back to the actual machine design. The experience was quite worthwhile, and more to follow on our actual design decisions, but for now these images will begin to convey the work we put into building this monster of a design project. And remember, we not only made design decisions and modeled each component, but also machined and assembled everything here.
The 18V Dewalt drill motor and belt drive assembly
A good shot of the mill bit (3/8" 2 flute) and work table, with a "sacrificial" piece of Al bar stock on board
A sample light cut (long traverse) and a full width, high speed, high depth-of-cut (jagged death-looking traverse)
The mounts for the two tables, with flexures visible
Our special flexure for the lead screw thrust nut. Works incredibly well, allows around 1/8" flex in any direction, but holds several 100lbs axially
Our vertical bed translation axis, using a 6in main support column and 5/8in drill rod for translation.
Kinematic Coupling joining our spindle to the support neck. Theoretically allows us to change to other head attachments while maintaining endpoint accuracy
Rapid Protocasting
Today was, among many reasons, an excellent day. After hardly sleeping, I awoke strikingly early to a warm spring morning, and had an early meeting with Hugh Herr, leader of the biomechatronics group over at the MIT Media Lab, where we talked about some work I could do for him that might be of some mutual interest. I then immediately picked up some books for my American Revolution course, skimmed the relevant passages, and felt I knew enough to head to class.
And then promptly skipped the first half hour to do something AMAZING. I’m taking 3.042 this term, a course focused on working an independent project as if you were an internal project in a company. The project I’m working on is using 3D printed concrete to create molds for metal casting. The problem, which you will see after thinking for a few, is that concrete melts at the temperatures of molten steel or other alloys. This makes molding less of a useful thing and more of an exercise in futility.
Nonetheless, I skipped class to do the first step of our experiment for the day; a real live steel pour. The tech my team is developing, see, is a ceramic slurry which can be slip cast onto the concrete mold. As the slurry is poured into the mold, the concrete sucks out the liquid, pulling the ceramic particles in the slurry onto the surface of the concrete. Once a thick enough layer is built, the remainder of the slurry is poured out of the mold, leaving a thin particulate ceramic covering the mold. Firing the baby in a furnace sinters the ceramic, and a beautiful, thin, hard, high temperature coating is left on the mold. I did this for about 6 different test pieces, using different soak times in the slurry to build different layer thickness, leaving several nice looking molds with our most successful ceramic layer to date on the surface.
I went to the rest of my classes and the magical hour of two finally came, when 3.042 starts and we could finish our experiment. Now that we had a few sample molds with high temperature coatings, we did the only thing you can do with such a trite object, which is pour many pounds of 1600 degree Celsius brilliantly bright steel into them and pray the molds don’t explode. The pour went fairly brilliantly, and we should have fairly good baseline data to push our experimental exploration in a solid direction. All things considered, an ace day for an ace project.
Stay tuned, soon we’ll be CADing up all kinds of crazy shit just to make molds and cast it in various high temperature alloys. Flywheels, hands, pretzels, whatever we can think of, we’re going to cast it and see what happens! Whoo, Science! No, not quite, ENGINEERING!
Till then,
Cody Daniel
Molds ready for casting
A microscope image of the ceramic layer we use
Here's a cast impeller using our process
An example of a cast flywheel we did