Has anyone ever used .250 pitch chain and sprockets for their x axis over belt drive? I like it because it doesnt stretch or shrink over time compared to that of belt and still have good rapids.
I raided about 30 feet of chain from three "destined to the scrape yard" 6 ft. plotters (its amazing whats in plotters for parts and pieces. I got my drilled and tapped 5ft 10in 16mm rails out of one plotter) and various sizes of sprockets and I'm thinking of using it over belt.
The chain fits nicely into the groove of 80/20.

One question I have about this is the size of sprocket to use. Is there a formula to determine the distance of travel per rotation for various size diameters.
I could probably quite easily just set up the existing sprockets and measure the travel of the chain per rotation, but suspect its probably going to give me an odd distance to divide for stepping. I'm wanting to get the correct sprocket size for easy stepping calculations. I'm just wanting plain ease over all.

I can remember seeing some big machines using chains between the servo's and screws.These were bridgeports.

I don't think it would make much sense unless you know how to make them backlashfree wich is not an issue with the rubber tooth snare's.
I guess the stretching shouldn't be that much of an issue cause you should tension your belts and can do this as tight as you like and a bigger rubber snare would probably solve any strength issues.

sorry i can't help in actualy putting the chains to use.

just my 2p's

This is the best example of chain drive on this site.
http://www.cnczone.com/forums/showthread.php?t=14743

The "formula" that you seek to convert distance traveled as a function of rotation relates to the pitch diameter (PD) of the sprockets you choose.

Once you know the PD, some simple multiplication or division with Pi is all that is needed. Since the dial on the handle probably has intervals engraved upon it, all you need to do is count the number of intervals and then, again using the fact that there are 360 degress per rev, you should be able to convert degress of rotation into thousandths once you know how long the PD circle is from your selected tooth count.

Chain and gear drive problems don't have a one size fits all solution. Rather, they are typically solveable by bits and pieces using simple, readily known relationships and a bit of math.