Hardwood CNC from wood on a budget, Possible?

[Neale]

Let me add my twopennorth as someone who has built and used an MDF CNC router, essentially to the JGRO design. There aren't many people prepared to admit that...
I have a cutting area of about 800x400, from memory. It uses skate bearings on steel tubes and threaded rod. On the plus side - it works. On the down side - only just. It's difficult to get a flat bed, to adjust the bearings and keep them adjusted, and generally to maintain any kind of consistent accuracy. There are better MDF designs but I doubt that they will entirely remove all these problems. As Jazz has said, show this stuff a cup of coffee and it distorts. Take the coffee away, and it will sulk and distort again, but probably not back to where it was. Warm/cold/damp/dry - any change in weather and you will be re-tweaking. All that, actually, might be bearable except that you have to keep cutting speeds so low to avoid major structural distortion - or failure - that big jobs can take hours rather than minutes. OK, I use threaded rod as leadscrew material which limits X axis speed to about 800mm/min, but frankly the thing couldn't take much more anyway.

As far as accuracy is concerned, I cut a series of interlocking 9mm ply panels for an architecture project and had reasonable repeatability, although not absolute accuracy - that is, I cut some samples, tweaked the dimensions slightly, and then cut a series of pieces that fitted reasonably well. It works pretty well for engraving, as long as you can level the work.

I'm halfway through a build of a steel framed machine using profile rails and ballscrews. Is there a message in that?