This post is to address how this project has been thought through, to qualify for the 2017 HaD Prize.

The short answer is that most design aspects have been refined from previous iterations of the mill, so a lot of problems have been caught already. Some of the big concerns:

• Alignment/being square: This was mostly addressed by fabricating all parts on a mill, ensuring they're square. Alignment was solved in 3D CAD (for the design), and using dial indicators and whatnot when machining the parts.
• Rigidity: Since this machine is designed for milling aluminum, rigidity is important. I'm far from a mechanical engineer, so my solution was "throw lots of metal at it and how it's fine". So far that seems to have worked. I'd always like it to be more rigid, but it's pretty darn good right now (removing 3 cubic inches/minute of aluminum).
• Work area: The previous versions wasted a lot of potential work area via dumb design. This iteration seeks to take advantage of the full possible travel of the machine- again, designed in 3D CAD
• Precision: Previous iterations were... sloppy, in the most literal sense. Lots of backlash, runout in the spindle, and lots of play in the bearings. This version takes great care to use quality leadscrews (ballscrews!), drives, couplings, etc. to minimize these issues.
• Control: This was fortunately already solved from a mishap years ago- LinuxCNC/Machinekit + BeagleBone Black = awesome. The BBB has realtime units built in that lend themselves VERY nicely to motor control, while the main CPU runs the UI. It's not the fastest UI on the planet, but it works.

Two big unknowns remain: Chip removal and an enclosure. The first I hope to solve by building an air blast/mister system to blow the chips away from the machine, instead of letting them pile up and manually removing them.

Enclosing the machine shouldn't be too much of an issue. Right now I've got some plastic pieces I clamp on to mostly keep chips out of my face; it would be ideal to have that extend around the entire machine.

Adding ways covers would probably be a good idea as well, but I don't have a good solution for that yet. It works without them, but it would be great to not worry about chips getting in there.