Lauri,
I've had to resort to wrapping a set of water pump pliers in cloth and using that to turn the inner knobs on two of the machines we've bought. They were just so tight you could not turn them by hand. Nothing binding them, no rust, no crud, they had just been cranked down too tight. One of them actually has plier tracks on it.
Oil it first of course then if that don't work wrap a set of water pump pliers with rags and get a grip on it.
Joe