I found...

[amurphysmu]

I happened to come across 8, 1/2" x 22" pieces of precision ground, hardened stainless steel rod in my school's engineering shop and the lab manager said I could just take the stuff. How big of a machine should I attempt with 1/2 shafting? Would 21" or so of unsupported shafting like this flex.

The other day I picked up a 36" x 36" x 1/2" chunk of 6061-T6 for $50 and plan to build my machine from it. I also picked up some big old 1"x10"x24" chunks of that plastic they make cutting boards for $5 from the local plastic shop. Does anyone have any experience making linear bushing from plastic sheet?

My plan is to build my router, for less than $200.

[jeffs555]

A 1/2" round steel bar 22" long and supported only at the ends, will deflect 0.024" for each 10 lbs of load. You can download this freeware program to calculate deflections for other lengths and diameters.
http://www.geocities.com/richgetze/

[chuckknigh]

Of course, you could always put it on top of a U channel extrusion, and support it. Several people have done this, and the results were exemplary.

-- Chuck Knight