I had the chance to dig through a couple of my boxes of "stuff I think I might need for a project some day, maybe" today.

Among the spoils were some excellent-looking little stepper motors (all the same model). They're hybrid motors with 3.6 degrees/step. I remember buying them years ago for a stepper driver project, and it seems like I'll get to put them to good use. I was happy I had four of them; CNC lathe mod!

I also tracked down some small micro-switches that look like they'll make excellent limit switches.

Also, since I want to add a manual control option to my stepper drivers (mostly for fun), I located some old arcade controls. These I bought a long time ago for a MAME cabinet I was designing. Hurray for another project that got postponed indefinitely!

So, I've been working out a lot of options for the mill frame. I want to try to build a rigid skeleton frame (rather than using solid stock or boxes made of sheet steel). While I like the idea of using water pipe for my frame, I decided early on I want a more square and uniform mounting surface for my ways/guides.

I've considered using Uni-strut (the stuff used for plumbing and electrical work) because it's easy to get, relatively cheap, and is enormously rigid. However, the easy-to-acquire dimensions are a bit larger than what I need, and the U-channel profile limits my design options a little. I had nearly settled on buying square-tube metal stock, when I remembered I have about 80 feet of data ladder racks hiding in my shed. (I seem to get phone calls whenever computer-looking things are being thrown away during commercial/industrial renovations. Does anyone need a telco-style aluminum data rack? ...or two?)

The outside rails on mine are pretty decent-looking rectangular tube stock 1-1/2" x 3/8" with a tube wall of .0075" (powder coated). A single span of this stuff is most likely not rigid and torque-resistant enough for my mill frame. However, since I have so much of the stuff, I'm considering a quasi-laminate structure of stacking two tubes against each other on the long face, and welding a bead down the contacting corners. If that works out (and doesn't take weeks of work to finish), I might build the frame around two C-shaped frames that form both the foot of the machine and the support for the tool and Z axis. The C-shaped frames would be built like half of a picture frame (mitered ends and welded), and possibly (most likely) some 45-45-90 steel plates welded on the insides of the two corners for extra rigidity. Those would be bolted together with some cross-pieces to keep the whole frame upright and square. This Wednesday, I'm going to head over to my friend's machine shop and see what my options are for working with these ladder racks (how easy it is to grind off the powder coat, if I'm able to weld solid attachments on such thin walls, etc).