Mill Assembly 06

Here's the latest update to the design. A number of changes were made based on manufacture-ability of a few parts.

This update includes:

- New 1/2" linear guides
- 1/2" shaft collars w/ set screw detail
- Bracket screw detail
- Y-table detail based on new aluminum T-slot extrusion
- Minor adjustment to upper frame cross member (due to a happy mistake in mounting), it's now more secure
- Z-axis brackets are now simplified, and wider for additional support and ease of construction/adjustment
- Material updates