Double Punching Diskettes

Chuck Guzis cclist at
Sun Nov 26 16:42:21 CST 2006

On 26 Nov 2006 at 13:16, Fred Cisin wrote:

> The "deluxe" models of both had a peg and donut for putting on
> center hub reinforcers.  EARLY DD 5.25" needed them.  And then
> they stopped putting them on with the HD disks.

IIRC, it wasn't the diskettes so much as the clamping arrangements on 
the drives (Shugart had the most reliable system, but sued anyone who 
tried to copy it).  It was quite awhile before someone figured out 
that turning the spindle motor on when a diskette was inserted so as 
to center the hub in the clamping setup was a stroke of genius.  I've 
got some old Micropolis single-sided drives that will mangle a hub in 
fewer than 10 insertions.

A few HD manufacturers put the hub reinforcement on their disks early 
on.  I didn't think it did any harm, but it didn't help either and 
was nonstandard.

I recall getting a very angry call from a customer who said that 
CopyQM was making unreliable 5.25" DSDD copies--that he'd make and 
verify a copy and then found it couldn't be read by another machine.  
What he didn't mention is that he was using the PolyPak equivalent of 
diskettes--no-name mail-order cheapest possible.  I asked him to send 
a few of the failures our way and we'd have a look at them.

It turns out that whatever bit of machinery that was used to apply 
reinforcing rings had applied TWO to each side, each ring being 
slightly offset from the other.  The diskettes would never center on 
the hub the same between any two insertions.  After I pointed this 
little tidbit out to him, the complaints stopped.


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