7 Sep
2016
7 Sep
'16
9:17 a.m.
On Sep 7, 2016, at 11:56 AM, tony duell <ard at
p850ug1.demon.co.uk> wrote:
Did you construct an engineering drawing of the hub based on your observations?
The other question is the disassembly of the pack
and the installation
of the new hub. How is that done? What are the concentricity
requirements for the platter? Is there a mating surface (exterior cylinder
surface on the hub) or are platter and hub aligned in some fixture and
then clamped to hold the platter in position? Clearly the pack would be
reformatted, so a small amount of runout would be ok, but it would have
to be small enough that the vibration is controlled.
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. 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), give or take. Another option
would be to make a centering jig, one that holds the hub and platter. If the outer
diameter of the platter is held to tight tolerances that would work well; if that
dimension is not tightly controlled then centering with an indicator gauge will work
better.
With a spare spindle like that, you'd also be able to verify the balance afterwards,
by spinning up the finished platter and checking the vibration level.
paul