Shugart 800-8 media centering problem

[Jay Jaeger]

On 8/14/2015 3:01 PM, tony duell wrote:

> 
>> The clamping is not out of alignment.  If it were, the results would be
>> more consistent.  Besides, the clamping is not really responsible for
>> the alignment.  It is a matter of the media relationship to the spindle
>> as the clamping comes down on it.

It can indeed.  If, in that process, the media is sometimes pushed a bit
forward, back, or to one side or the other, then the media relationship
to the spindle IS affected - particularly in this case, as the drive is
upside down from the normal orientation, where the spindle is underneath
the media, and gravity cannot help it find its way to the center.

> 
> The fact that it sometimes centres properly suggests to me that it is not
> excessive runout on the spindle, but none the less the first thing I would
> do is remove the clamp arm and check the inside surface of the spindle
> with a dial guage while turning it by hand. Then probably take out the
> spindle and its bearings and check all the parts are there (compare with
> the service manual or the good drive). If something there is coming out
> of place it will cause big problems.

There is no play in the spindle at all.  Certainly not 1/2 track worth.
 Can't wiggle it at all, no visible wobble, etc.

> 
> Take the centring cone apart (there are lots of bits and at least 2 
> springs) and again check for anything missing. Make sure the spring
> are in the right places, if you swap them over the cone will not expand
> properly and will thus not centre the disk properly.
> 

The centering cone/clamp has just one continuous spring, all the way around.

And, there is no point:  I did mention: I swapped those plastic
centering cones / clamps with the other drive, and it made no difference
to either drive.

> Now look for wear on the 2 main plastic bits of the centring cone. If
> the inner part sticks, again it will not centre correctly. If there's wear
> on the outside of the larger part, the disk may not run true.

See the above.

> 
> -tony
> 

Polishing the cone on the spindle helped, but just a small amount.

I did also discover that the head load armature assembly was somewhat
canted, and could, barely, interfere with the head pressure on the inner
tracks.  Corrected that - again, not much help with the other problems.
 And when this thing is off center, it affects all the tracks, of course.