jig for Twisted-Key keytops

[Paul McCloud]

What I'm saying is that if the key is twisted, and you lay it flat on
your jig, the keytop may not be exactly parallel to your jig surface.
Try taking a key from a piano and lay it flat on a known flat surface.
Especially old keys from a large upright.  Push down in the middle of
the key.  Some keys will flex a little.  Maybe it's not enough to notice
for most keys,  but if there's any twist in the key, your planed surface
may not be parallel to the bottome of the key.
    Paul McCloud