Low level HD recovery?

[StuartR]

I learned all this stuff over many years working as a hardware engineer, originally working on disk drives the size of a washing machine and then being amazed as they grew smaller and smaller over the years. We used to adjust the head height mechanically using plastic measuring shims, modern disks have a flying height measured in nanometres, it really doesn't take much to disturb that.

This article has some helpful information about disk heads and flying heights.

[ErikJan]

Thanks for the article. Interesting but I knew that already. I'm still not clear on the whole thing but it seems I'm stuck and there's no way out ;-)
Thanks for your patience and help Stuart, it's appreciated.