Shugart 800-8 media centering problem

Jay Jaeger cube1 at
Sat Aug 15 20:55:30 CDT 2015

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


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