I'm changing the pulls on kitchen cabinets. About half came off very easily. On the others the porcelain part has come loose from the brass stem that runs through it so when I turn the knob while holding the screw the porcelain turns but the stem won't budge. If I try to turn the screw while holding the knob the screw turns the whole brass piece. What to do to get these off without damaging the wood door?

John Swaro