To go from 18x20 to 16x18 is easy enough. Just skip the last mains and top/bottom cross. You can also do the 16x19 pattern by skipping last mains and just the last cross at the bottom. Should be no frame integrity issues. You can't do anything about central main spacing, but I suspect the the string bed will be slightly less stiff.
Addendum: May have to find new tie off holes.
Last edited by esgee48; 01-13-2013 at 04:28 PM.