5 Jan
2014
5 Jan
'14
8:42 p.m.
On 01/05/2014 03:49 PM, Mark J. Blair wrote:
Back on the floppy subject, I think that the trickiest
detail about
making an alignment disk writing jig would be calibrating the
micrometer reading to place the head gap at the correct radius. One
way might be to get an original known-good alignment disk, calibrate
the jig against it, and then use the jig to crank out new alignment
disks for sale to hobbyists. I would imagine that the disk drive
manufacturers had some way to measure the radius of a written track
for calibration purposes in the lab?
I suspect that a good approximation might simply consist of taking a
drive and placing the disk clamping mechanism so it rotates a bit
off-axis. I remember this happening in response to a customer
complaint--he had picked up a batch of floppies where an extra hub
reinforcing ring was placed on each floppy.
The result was that, although the floppy was clamped somewhat
off-center, it formatted fine and verified the copy of data placed on
it. Remove the disk from the drive and put it back in and almost
nothing worked. I nearly went bald with frustration, until I noticed
the extra ring. Removed it and everything was fine.
(This is what happens when you buy floor sweepings for media.)
So if you intentionally wr0te a bunch of off-center tracks, then
transfered the disk to a known-accurate drive, you could see what ID
header was in exactly the correct center-of-track position.
Cheap, but perhaps effective.
--Chuck