[rweatherly]

I think the unloaded accuracy is very good -- if you don't load up the tool, it should be as accurate as the leadscrews, alignment, backlash, etc. My machine was all made by hand, to the drawing, and no real pains were taken to align it. I tested my machine by machining 2" squares out of 1/4" hardboard. Depending on the direction I went around the square, the dimension was out about .020" (+.020" in both dimensions when cutting CW and -.020" in both dimensions when cutting CCW -- I could have the CW and CCW reversed, but you get the idea). There is no doubt in my mind, that if the tool had little or no load, the squares would be within a couple of thousands, so if I needed an accurate final dimension, I would save a light cut for the last.

That said, I have engraved some 4" high text into wood that look perfect.

I like the machines that have the pipes fully supported, but on my machine when I manually pull the spindle perpendicular to the rails the spindle deflection is about 10x the movment of the rail, so a rock solid rail is not going to cure all problems. The supported rail is going to help, so if I were going to make another machine I would do that.