When removing a pinned key that may also be splined, like the F# key on a flute, it's critical that you be aware of the information the key is giving you. If you remove the pin, and the key will not spin off of the hinge rod, that means it's probably splined, and can't be twisted off. Splined parts need to be driven apart, not twisted. Twisting harder will only yield one result - a broken hinge rod, and at least an hour of lost time spent making a new rod. Driving off the key simply involves securing the exposed part of the hinge rod in a machinist's vise (with all the other keys removed), and tapping the key toward the far end of the hinge rod (toward the D key, if the D key were still mounted on the rod). A few taps will get it off the spline and it can be slipped off the rest of they way by hand. To reaffix the key, I've found the best method is to chuck a piece of 2x4 in a large vise, find a spot close to the edge, and drill a hole all the way through that it slightly larger than the diameter of the hinge rod. Place the key on the rod, put the rod through the piece of wood so that the key is resting on top of it, then line things up and tap on the end of the rod until it's driven back into the key and everything is tight. In order to avoid bending the rod, the hollow-tube part of the key should be resting directly on the wood. The key cup be hanging over the edge and not touching any wood - that's why it's important to drill a hole close to the edge.
But if it resists when you try to twist it off, just don't twist it off!
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