Shugart 800-8 media centering problem

[Jay Jaeger]

On 8/15/2015 8:31 PM, Jon Elson wrote:
> 
> On 08/14/2015 02:58 PM, Jay Jaeger wrote:

No, I didn't write any of what was quoted.  ;) If one is going to remove
the entire message quoted, then it probably makes sense to delete the
"wrote" line as well.  ;)
> 
> The way most of the old 8" floppies work is they have a cylinder with an
> ID that matches the ID of the floppy hole.  The floppy sits against the
> face of the cylinder, and a plastic, springy cone is pressed into the
> cylinder by a bearing and spring on the loading arm.  This arm usually
> also lifts the head off the media when in the open position.
> 

As Tony discovered after checking one of his own SA-800 series drives,
that is not how the SA-800 series works.  In these drives, the spindle
is NOT a cylinder.  The spindle is a CONE on top of a flat part (all one
machined piece), then a shaft through the deck, to the pulley on the
other side.  The media sits on the flat part , just below the cone, and
the plastic springy CYLINDER (more or less), gets pressed OVER the cone
and on top of the media over the flat part.

> So, the first thing to check is if the plastic springy thing still has
> all its fingers.  If fingers have broken off, the result is obvious.  If
> all the fingers are still there, check for smooth sliding into the
> cylinder.  If the fingers have gotten bent or rough, the clamp may not
> always seat reliably against the hub.
> 

Had you read the whole thread, you would have read that I had already
examined the "plastic springy thing" (aka, the hub clamp), and found it
to be healthy, and HAD ALREADY SWITCHED IT WITH ANOTHER hub clamp THAT
WAS on a working drive with no change to either drive.

> Finally, the spring or bearing may have a failure, not driving the clamp
> into the spindle.
> 

The hub clamp is engaging onto the spindle just fine, thank you very
much.  There is no bearing of any real import in the hub clamp, really,
just a screw through (perhaps) a little straight bearing.  The spring in
the hub clamp is obviously fine (and, again, it had been part of the
assembly I switched with another drive).

> Almost certainly, careful examination of these parts will reveal the
> problem.

No, careful examination most certainly did NOT reveal the problem.  At
this point, the best guess is either that the clamp arm is out of true
(unlikely), a grove that cuts into the cone at its bottom, allowing the
media to shift, or a spindle problem (bearing, not the correct shape any
more, etc. etc.).

> 
> Jon
> 

JRJ