[MikeA]

First Hu there is no feedback on most stepper systems (I believe there are some drivers that will except encoder feedback). You are at the mercy of the machine. That being said, the old machine with the drivers it had, I knew what my max speeds where and just didn't push it. In processing a 4x8 sheet of material, most fully nested with some type of pattern, and then rehomed I would be off .003-.005" at most. Most wood or plastic workers can't even measure that, especially over 8'. I believe most any newer drive system supports circular interpolation in all axis', as does the Flashcut system. As far as tuning the system this is not required as in a servo unit, although there is a series of ramp up and down settings, baud rate, and other misc. settings in the software that have to be set. That requires a little bit of experimenting with your paticular machine. As far as the pinion set to the rack I slipped a piece of teflon pipe tape and meshed the gears tight together. I had direct drive on .5" lead ballscrews on the other axis' so I used a timed belt and pulley to acheive basically the same lead or as close as I could get. I originally looked for a Nema 42 gear reducer to try to acheive the right reduction, but they cost as much as a ballscrew and there is more inherent backlash than using a timing belt and pulleys. The rack was a 10 pitch 14.5 degree and I used the smallest toothed gear which I believe was a 10 tooth. Z, as far as your project, I wouldn't be scared of rack and pinion, as there a lot of routers out there using them, new and old. My concern would be the longevity of the less expensive racks and gears, but I guess the cost savings would allow you to replace them periodically if you had to. Mike