12 Mar
2014
12 Mar
'14
1:12 p.m.
----- Original Message -----
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
To: <cctalk at classiccmp.org>
Sent: Tuesday, March 11, 2014 7:54 PM
Subject: Re: Convert PDP-11 RK05 disk pack to PDP8
Whats the track width on an RK05, I semm to recall its 100TPI so thats
10thou per trak, add a bit of guard space so maybee 8thou track width ? if
you have 1 or 2 thou exentricity ok, more and could lead to
interchangability problems ?, mind you 4 thou out may meen its vibrating so
badly that this is the least of your problems.
Dave H
Hi,
Sure. The onyl reason to have it well-centred it to improve mechanical
balance and reduce vibration. i've seen photos of people at the factory
inspecting disk packs
(admittedly the 5 and 10 disk ones) with a dial test indicator to check
the cnterign of the platter(s). I would assume that was necessary.
I claim that it
was (only) better to do that. Well centered disks
minimize noise, vibration, and wear at the spindle bearing.
The disk surface has no relationship to where the tracks will be written
onto it. I wonder if excessive vibration could end up makign
the heads more
unstable and more liable to crash.
In any case, it can't hurt to get it centred as accurately as you can.
I doubt that's the reason, surely all the disks awere made in the sme way
to pretty tiget tolerancs. In any case I mentioned a drive that used a
'naked platter' from such a pack as the fixed disk, which was located by
the centre hole. AFAIK any spare platter would fit.
I thoguth I saw somewhere that the trace of wanter had to be added, adn
that even purer proan-2-ol was nto ideal.
-tony
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If the centering is as non-critical as you
suggest, I wonder why there
wasn't a machined regiser (step) on the hub, so you could just put the
platter on and clamp it up
Perhaps they planned to use disks with different inner
hole diameter? I
was wondering about that as well. Very impracticable. I thoght the correct cleaner did contain water
(something like a 91%
propn-2-ol to 9% distileld water mixture)
Yes, they say 91% alcohol. I assume that
they meant "at least" 91%...