Rust on tape heads

[John Lawson]

On Wed, 1 Sep 2004 pzachary at sasquatch.com wrote:

>
> I guess I should have been more specific, and say that 3M company makes a
> line of abrasives that use the scotchbrite technology but are MUCH finer,
> (10000 grit or so I think is the bottom end, I don't use anything finer
> than 1800) and these have supplanted most of the bar substances in the


   Yup - to re-iterate, I have successfully recovered large audio heads 
from foriegn-object damage (slipped screwdriver, shipping damage, etc. - 
ouch!) by using a strip of cleaned linen to which has been applied a *very 
light* paste of mineral oil and jeweller's rouge - or, as mentioned, 
some other exceedingly fine grit abrasive powder. This is then 'seesawed' 
very gently across the pole faces in the same direction the tape travels

   In cinema audio work, where the heads were typically 30MM tall and have 
from one to six poles - the three-track pole faces are 1/4" *each* - after 
lapping them, we typically used a short continuous loop of some crap mag 
stock, which would run for an hour or two, to 'condition' the head and lap 
it in to it's final shape - using the natural abrasiveness of the media 
itself to finish the job.

   But none of this is for the faint-of-heart - ya gotta go slow and think 
about what is being done, all in terms of a knowledge of the physics and 
mechanics of tape-recording head technology. No matter what the signal or 
the number of tracks, the mechanical aspects remain the same for all 
classes of static-head machines.


   And most certainly you are dead-on about first taking the decision as 
what the ultimate end is - is this for a museum? Hobby machine? Critical 
application?

  Cheers

John