n these picture the 3/4" dado plane is being used but the same principles can be applied to using any size dado plane. Your dado planes will cut up to 1/2" deep and you can accurately set any depth up to 1/2".
The top photo shows a wide piece of cedar from one side of a shelfing unit held flat on the bench with a tail vice. A large home made square is positioned where I want the dado cut and the plane runs up against the side of the square to form the dado. You can hold the square with one hand and plane with the other as show in the second photo or you can use a clamp to hold the square and use both hands as shown in the 3 rd photo. Either way ensure the square is sitting nicely on top of the wood, as any movement in the square will result in a rough dado.