G’day; the simplest method for you would be to use a fairly
coarse round file, starting with a file a little smaller than the
original hole. I’ve done a ‘few’ that way.
The ‘correct’ way to bore rubber and cork stoppers is to use a
tube sharpened at the end, lubricated with good old spit or more
hygienically, with glycerol, but NOT any oils. One can buy sets
of what we used to call ‘cork borers’ varying from 1/8" to 1",
and available from lab suppliers. Memories! I must have bored
literally hundreds of corks and rubber stoppers in my time. When
I was a lab boy (in 1936!!) I used to have to get apparatus ready
for whole classes of junior chemistry students every day, and
that included vast amounts of cork boring! I hated it!
/\ John Burgess
/ / Johnb@ts.co.nz
(_______) In sunny temperate Mapua NZ -
Autumn’s here and winter’s close