i have an acme thread assembly that consists of two blocks on either end and an acme thread between them.  i have designed it in such a way that the block are mated parallel to one another.  as i move one of the blocks and change the distance between them, upon rebuild the acme thread will automatically change lengths.  the idea is that i can take several iterations of this assembly and insert it into another assembly, fix both blocks in different areas and have it automatically redraw the whole thing.  i have tried everything imaginable to do this, even as far as redesigning the assembly different ways.  in all cases solidworks will either lose certain parts or features or give me errors that make it impossible for me to rebuild and have the acme thread properly rebuilt. any ideas appreciated.