Ketil's video 
http://www.youtube.com/watch?v=_BqRBYM4YxU
is great. Little sad that the sound just doesn't come across at all, but
otherwise his demonstration is very clear.

Okay: I don't cut the upper side of a plectrum "so it goes slightly
downwards". I had 3 years of lessons on another of his harpsichords of the
same type, which had very clearly upward angled mortices and - as a result -
quite annoyingly over-plucking plectra, so maybe this is his answer to that
type of angle. If I would cut the tip of a plectrum in any of my instruments
in his way, it would probably start slipping before plucking. Also, bird
quills don't really respond well to an excess of tampering, they only get
less sturdy.

Personally, I prefer scissors for some of the work, like tapering the strip
of delrin and cutting the front tip - a personal choice. Otherwise no
complaints...
I particularly like his reference to the audible result. Of course it is
always nice to know about the exact reason of some or other effect, but most
of the time it's really enough to know how a certain manner of doing works
out in practice.

Tilman

www.skowroneck.de