13 Apr
2000
13 Apr
'00
2:27 p.m.
When you're exercising these drives, be certain you don't step them too
slowly, unless you go at rates on the order of 30-60 ms per step The
slightly-too-slow step rate provided by most systems is the WORST and not
"nearly right" as many people believe. Standard SHugart 800/801's tend to
work pretty well at 6ms/setp, though they're spec'd for 8. The lead-screw
drives in general, won't step at a rate faster than 5-6 ms per step, and
some won't do even 6 ms steps. What I'd recommend is that you attempt to
work them at 8 ms until the lead screw is quite nearly free of contaminated
lubricant, and then try them again at 6.
Stepping too slowly causes major stresses on the system because it is still
ringing when the next step is taken. This puts pretty hard vibration on the
system along the axis of the lead screw. That then puts lots of stress on
the plastic head-assembly that contains the "nut" and it causes acoustic
noise. If you're VERY close to the "right" rate for the individual drive,
it will be very quiet. That's what you want. If you run 6 ms drives at 8-9
ms, they'll be prone to vibrate and make lots of noise, so you'll know it's
wrong. The most likely victim will be index alignment, which normally
relies on a single screw to hold the sensor in place. The radial alignment
will suffer as well. You needn't concern yourself about azimuthal
alignment unless you've taken the head positioning mechanism apart and
loosened the guide rails.
Depending on what sort of controller you use, you may find it beneficial or
even necessary, with these old drives, to change the rate at which it steps
by moderately extensive alterations to the subsystem timing in order to
minimize the effects of system vibration.
Dick
----- Original Message -----
From: <CLASSICCMP(a)trailing-edge.com>
To: <classiccmp(a)classiccmp.org>
Sent: Thursday, April 13, 2000 12:25 PM
Subject: Re: Lubing Shugart 800,801's?
backlash
of
and
when
When they say
"do not lubricate ..." they're not lying!
If only the previous owners/techs had understood this!
> The grit and grime
>that finds its way into the leadscrew will act as lapping compound and
>abrade the lead screw, which in most of the newer lead-screw-driven
>mechanisms is plastic, and soon, you'll have a drive with too much
>on the lead screw, which will result in
positioning error, depending on
the
direction in
which the lead screw was last moved.
I've got 14 Shugart 800's and 801's from this latest pile now undergoing
the DSD Hyperdiagnostics simultaneously (lots of head kerklunking!)
and I see no evidence of alignment problems on any of them. I'm strongly
of the opinion that 95% of alignment problems are created when folks go
in and fool with the alignment when there's nothing wrong in the first
place.
> I would probably feel
>comfortable cleaning out the gunk with a penetrating oil wuch as what you
>mentioned, but I would vigorously pursue the problem of getting the rest the sticky
residue out with a volatile solvent.
I think "Liquid Wrench" is both a penetrating oil and a mix of volatile
solvents. And in spraying it in I added my own oil to the lubricating
mess that shouldn't be there, but now at least I can turn the leadscrew run the drives through their paces.
>That, in turn, threatens to soften the plastic head-assembly, part of
which
>is the "nut" for the lead screw, so
don't get any of the benzene or
methyl
>alcohol, or acetone, on the plastic parts, lest
they soften and change
their
shape.
I appreciate that, I learned long ago to test chemicals against plastics a can of TV tuner I had dissolved the plastic shaft in
an old TV...
>I'd suggest that you look at the service manual and consider whether this
>bothers you enough to warrant going through the painstaking process of
>disassembling and cleaning the head transports in order to get rid of the
>grease. If you're careful, you might find a way to brush out the
threads,
>but they'll continue to accumulate dirt and
grit so long as you have
grease
on the
"nut" which is part of the head assembly.
Yes, I can do a halfway decent job with skewers and Q-tips to get the goo
out of the threads, but there certainly is some still left in the threads
on the head assembly/pre-load nut and that I can't get at without
removing the whole assembly and destroying the (currently fine) alignment.
Tim.