3.5" floppy failure mode? Hub not attched to media.

Fred Cisin cisin at xenosoft.com
Thu Feb 26 16:14:53 CST 2015

> > I've never had luck reattaching the media to the hub when it becomes
> > detached.  (I've used a dab of thin but sticky glue.)  I chalked it up to
> > not being able to get the alignment perfect,

On Thu, 26 Feb 2015, Eric Smith wrote:
> That seems quite likely. The track pitch is less than 0.2 mm. A
> positioning error of less than 0.1 mm when reattaching the hub will
> render the disk unreadable.

Same basic problem occurred occasionally in >3.5" media with misclamping.

That could be confirmed by reformatting a track and then checking it.
(Outer track preference in allocation would make innermost tracks the
least risky to sacrifice)

But confirmation of the specific problem doesn't solve it.

Idle speculation:
If it were truly important to fix it, you would need to build a hub
assembly that could be offset in two dimensions, such as a 4 jaw lathe
chuck.  Then use disclosing fluid and a good magnifier (reticle?) mounted
to the drive frame or head carriage, and turn the disk and look at the
amount of runout, readjust, recheck, readjust, recheck.  The idea would be
to offset the center of the hub relative to the center of the spindle.

NO, I have not ever tried to do it.

If anybody ever succeeds at optical reading of a non-rotating disk, ...

Grumpy Ol' Fred     		cisin at xenosoft.com

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