Thanks guys for replies. Joe, your comment on slack cables is a fair point but I use the Akerman steering geometry approach (like the steering mechanism in your auto) and ensure both cables are taut, only when the control surface is neutral and sweep the horns on the surfaces about 15* rearwards. This gives differential movement and prevents undue tightening of one cable due to unequal geometry. The airflow keeps tension, where you want it, on the surface. This I knew worked OK on the rudder but I was a bit unsure about elevator. Don't want an unneccessary problem on my new scratch built big bipe!!!