Have to disagree with Bazle.
If the keyway is at the botton, the key WILL do as he says, and fall out of the shaft.
At the top the key stays in the shaft, or or did for me, on the two times that I have removed the Apron.
Maybe Bazle was thinking of the key staying in the worm, rather than the shaft?
In the worm, it is easy to knock it out of position when re inserting the shaft.
Howard