Emil. Thanks for the clarification. The wooden rollers I have access to are far less robust. I can see how those would work.
Steve. Adding time in terms of exposure actually reduces density of he final print, since the plate is hardened further than you wish and washing out takes more water and more "scrubbing" (note quotes. you don't really scrub anything.) I'm still experimenting with the proper ratio of time with the positive and time with the screen.... another of those long term experiments. Cutting the plates for smaller images was big problem for me but now I sometimes find a number of smaller images I want to do and expose them all on a single plate, cutting the plate down later, when it's exposed, hardened and ready for ink. Alternately, I'll ink and print the whole plate and simply cut the paper after the printiong process is finished. Paper is much, much easier to cut! The only issue is in finding positives with similar density- ones that will allow exactly the same exposure timing. Cutting the plate first has one advantage - I often get an extra strip from the trimming, useful for exposure testing.