RK05 packs

tony duell ard at p850ug1.demon.co.uk
Wed Sep 7 12:40:35 CDT 2016

> > 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?

No. There is no need for what I want to do. I just need to put an extra
notch between each of the sectoring notches, I think (I will have to 
investigate what happens with the index notch, the one at the odd
spacing). It was my intention to put the hub on a dividing head, carefully
get one of the existing notches over a slitting saw, then rotate and
cut the next notch, etc.

> > 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. 

Sure, done that often enough.

> 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....


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