[Al Skierkiewicz]

Green,
There are several good suggestions, I like Chris's chain in a "U" extrusion as a simple and effective approach. But a simple and lighter alternative is to wrap the chain around a sprocket (180 degree wrap) and terminate in a spring. The spring holds tension on the chain as the cylinder moves the sprocket. There is no need to have a bearing surface under the rack and no reason to hold the chain in alignment since that is automatic. This is similar to the loop approach discussed but doesn't add the weight of the second sprocket, bearing, and extra chain.