Some of the jewelry suppliers (Rio grande & Otto Frei) have
abrasive cord. (Frei's calls it 'Mitchell's Polishing Cord'.)
Search 'abrasive cord'. Lord knows what the abrasive actually is,
but it may be emory.
Not a name Frei made up. Mitchell’s is actually the brand name
printed on the spools it comes on. Stuffs been available forever…
(I had a spool of the stuff when I first started in the 70s, and I’d
got from an old watchmaker’s estate, and he’d been retired for 20
years already then… It’s available in a number of different types
of abrasive. Emery and crocus cloth, are the two main ones. Also in
several different weights/widths and shapes, ie flat strip, round
cord, etc, and several grades of the abrasives. Not all suppliers
show all the types in their catalog listings, so look around.
As to your suggestion, Brian, of using strapping tape to secure thin
strips of ordinary abrasive paper or cloth, I’ve found that the 3M
imperial abrasive film is wonderful for this. That plastic base it
uses is strong enough not to need additional backing if you wish. I
routinely cut thin (1/8 inch wide) strips to fit in and finish narrow
gaps and crevices in castings.
3M also makes, for the dental trade, already cut thin strips of
similar abrasive film, in several grades. It’s interesting because
they put two different grades, a coarser and finer grade, of abrasive
on the strip, so one half is the coarser grade which you use first,
then slide down to the second half of the strip for some finer
finishing action… Gesswein was carrying it, haven’t checked to see
if they still are in their catalog, but no doubt any 3M dealer could
order the stuff.