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