Originally Posted by
jsheerin
A VFD is not included with any the setups you mention. A VFD is commonly used to run a 3 phase motor / spindle. Is this what you're planning on getting? This is more expensive than using a router which you said you already had... If you want something to turn your router on and off, you need a relay and possibly a power supply for it. Add maybe $50 tops to your cost for that.
I use a G540 on my 4'x4' router with 1/2-10 5 start acme screws and Dumpster CNC zero backlash nuts. It works great for me. However, you will be limited in your top speed by screw whip. You will be even more limited if you don't use the multi start screw. I get around 250ipm with ~60" screws. At that speed they're starting to whip but not too bad. At 8' you will be limited to a lower speed. I'd look into rack and pinion, a bigger diameter lead screw (more expensive, less options for cheap zero backlash nuts available), or a rotating nut setup (a bit more expensive, but a lot more complicated to design and build) if you want fast movement, probably in that order.