A general rudder pull-pull question:

In setting up a pull-pull rudder, how do you get it done without the cables rubbing on something. Seems like every time I try to set it up, no matter what I do, I get some rubbing somewhere, either on the exit holes or a former somewhere. Unless of course I make the exit holes extremely long. I've tried straight shots, crossing the cables, varying the length of the servo arm, etc. So then do you simply let them rub or put them in tubes? Just wondering if I'm the only one with this problem. Thanks.