Using the basic construction for the Y-axis (double precision rod with bronze bearing sleeves), how wide can you go before deflection becomes a problem?

I am looking for a setup that will give me about 18" of cutting accross the Y-axis. I gather I would need to construct a Y-axis using aprox 28" rods. Assuming I am building the z-axis to the usual spec and mounting a Hitachi router, how much defelction might I expect at the center? Would this be too large of a span? I'm looking for about +-0.01" precision.

Thanks,

What's the diameter of the rod?

With a heavy Z and a full sized router, you'll want to keep that axis pretty short or use some big rod (Think 1" dia or more for that 28" span). I'm running a 20mm usupported rod on my 24" Y axis and using a rotozip as a spindle. I can deflect the y axis very easy. If I had a full sized router on there it would be rediculously amplified.

What'll happen is that router doing any kind of heavy cut will shake the Sh!t out of the Z which will cause torsional flex of the Y axis...

I was thinking of using 3/4" rod (close enough to 20mm), so you answered my question. What a pain! Supported rails add SOOOOOO much to the complexity and cost, but a CNC that couldn't cut a piece 18" wide is not of much use to me. :(

I'll post the question over at the Yahoo group as well for contrasting opinions, but I guess I knew the answer even before I asked.