Step 3: Drilling out the stem
This is the hard and slow part, drilling the vulcanite stem. I only went to 5/32" for fear of cracking, though I wanted 11/64". Step up very slowly using the smallest bit that will remove any material. I had to use all these bits.
Remove the bit regularly and clear the swarf, which somehow comes out in copious quantities.
I would recommend working from both ends instead of fighting all the way through. Before each new bit, make sure there is enough clearance that the bit won't go through the side.
I was very careful and still almost cracked the stem as in the second pic. Fortunately that is just a bulge with external splitting, not a crack - it is still airtight. Whew!
Wash the stem out well afterwards with running water. It will be full of vulcanite dust, which you probably don't want to eat.