Thank you very much for the feedback jazz, as well as all the other wealth of info and experience you've shared.

I can appreciate that approach for ease and probable reliability.
I would love to go profiled rail, but that decision is a matter of budget trade offs at this moment - I am at the point where I have a digital frame laid out and overall design idea but fleshing out the final product specs. I'll goto a seperate thread when the time comes.

As far as alignment, play, and tolerances... I'm shooting for repeatability more then accuracy. So long as the tool repeats (reasonably) I can make it hold size.

Which brings me to my last question on this topic then: What have been peoples experiences with regard to compensating for assembly errors with operating software? How much slack can the pc take up reliably?