7 Sep
2016
7 Sep
'16
10:40 a.m.
I looked into
this a couple of years ago with the intention of making
a 24 sector pack for an HP7900 (actually part of an HP9880). Starting
from a 12 sector pack of course.
This project got interupted by a house move and I've not gone back
to it yet, but I did discover there is no alignment ridge or anything
between the hub and platter. The platter fits on the flat top of the
hub, there is a clamping ring that is then screwed down to anchor
it.
Did you construct an engineering drawing of the hub based on your observations? My intention
was to put the hub on a spare spindle (I happen to
have a load of RK05 drive spares), put the platter on, turn it round
by hand and use a lever-type dial gauge to get minimum run-out.
That's like the procedure for centering a work piece in a 4-jaw chuck. With care and patience you can get it centered to .001
inches (25 um),
And as you said the only real requirment is to get it balanced to avoid
vibration. I think a 1 thou runout would be good enough for that. Of
course the disk would have to be formatted after this modification
but that's not a problem.
In fact for my application (the HP9880) it may not be necessary. After
battling through manuals and microcode, I have realised that the
thing actually treats it as a _12_ sector pack, starting a read or
write on alternate notches only. That means an electronic modification
(easier for me) would let you use normal 12 sector packs that I
have over a hundred of....
-tony